569 results on '"Sharpless epoxidation"'
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2. Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study.
- Author
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Freindorf, Marek and Kraka, Elfi
- Subjects
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EPOXIDATION , *CHEMICAL decomposition , *ACTIVATION energy , *CATALYSIS , *ELECTRON density , *ALLYL alcohol - Abstract
In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study
- Author
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Marek Freindorf and Elfi Kraka
- Subjects
Sharpless Epoxidation ,Unified Reaction Valley Approach (URVA) ,local vibrational mode theory ,reaction mechanism ,bond strength analysis ,methy-hydroperoxide epoxidation of allylalcohol ,Chemical technology ,TP1-1185 ,Chemistry ,QD1-999 - Abstract
In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions.
- Published
- 2022
- Full Text
- View/download PDF
4. Stereo selective synthesis of C3–C12 fragment of iriomoteolide-1a
- Author
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Gangavaram V.M. Sharma and Karnekanti Rajender
- Subjects
Iriomoteolide-1a ,Mannich reaction ,Sharpless epoxidation ,Keck allylation ,Cross-metathesis ,Chemistry ,QD1-999 - Abstract
A convergent and flexible synthetic route for the synthesis of C3–C12 fragment of iriomoteolide-1a is described. The key steps are: Mannich reaction, Keck asymmetric allylation, Sharpless asymmetric epoxidation and cross-metathesis protocol.
- Published
- 2018
- Full Text
- View/download PDF
5. A New Formal Synthetic Route to Entecavir.
- Author
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Liu, Lixia, Sun, Yongli, Wang, Jiwu, Ou, Wentao, Wang, Xiaoji, and Huang, Shuangping
- Subjects
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BAYLIS-Hillman reaction , *HEPATITIS B virus - Abstract
We describe a new and straightforward approach to the formal synthesis of the hepatitis B virus inhibitor entecavir, an important hepatitis B drug, in ten steps overall. Key features of the route are a Morita–Baylis–Hillman reaction, a Sharpless asymmetric epoxidation, a reductive epoxide opening of an α,β-epoxy ketone, and a Riley selenium dioxide oxidation. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
6. Recoverable polystyrene-supported catalysts for Sharpless allylic alcohols epoxidations.
- Author
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Bartáček, Jan, Drabina, Pavel, Váňa, Jiří, and Sedlák, Miloš
- Subjects
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POLYSTYRENE , *ALLYL alcohol , *EPOXIDATION , *CROSSLINKED polymers , *ESTERS - Abstract
Abstract In this work, new heterogeneous catalysts intended for enantioselective Sharpless epoxidation were prepared. The catalysts are based on Ti(IV) complexes of cross-linked swellable spherical copolymer beads of styrene with ethyl-(4-vinylbenzyl)-L-tartrate, or with ethyl-(2 R ,3 R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate. These catalysts were tested in epoxidation of cinnamyl alcohols. High conversion (up to 99%) and high enantioselectivity (up to 99% ee) were achieved in the case of catalysts based on copolymers of styrene with ethyl-(4-vinylbenzyl)-L-tartrate (5, 20, 50%). Unfortunately, the copolymers lost their enantioselectivity due to the leaching of L-tartrate, caused by alcoholysis of ester bond. This problem has been overcome by replacing the ester bond by a stable keto bond. The prepared catalyst based on the copolymer of styrene with ethyl-(2 R ,3 R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate (20%) achieved a similarly high conversion and enantioselectivity as in the previous case (up to 99%, up to 99% ee) and was successfully recycled. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
7. Stereo selective synthesis of C3–C12 fragment of iriomoteolide-1a.
- Author
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Sharma, Gangavaram V.M. and Rajender, Karnekanti
- Abstract
A convergent and flexible synthetic route for the synthesis of C3–C12 fragment of iriomoteolide-1a is described. The key steps are: Mannich reaction, Keck asymmetric allylation, Sharpless asymmetric epoxidation and cross-metathesis protocol. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. Large-Scale Synthesis of Eldecalcitol
- Author
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Jung Jaehun, Hae Sol Kim, Chang Hun Seol, Seung Jong Lee, Kee-Young Lee, In A Jung, Seong Hu Park, Won Taek Lee, Hyung Wook Moon, Seon Mi Lee, Hyunik Shin, Bogonda Gangganna, Ji Soo Heo, Areum Baek, Kim Seung Woo, Chang-Young Oh, Jung Se Gyo, Juyoung Song, Seok-Hwi Park, and Kang Hee Lee
- Subjects
Sharpless epoxidation ,chemistry.chemical_compound ,chemistry ,Scale (ratio) ,Stereochemistry ,Organic Chemistry ,Epoxide ,Physical and Theoretical Chemistry ,Eldecalcitol - Abstract
Industrial-scale synthesis of eldecalcitol is described. AA highly diastereoselective epoxidation of p-methoxybenzyl (PMB) protected dienol at room temperature provides the key epoxide intermediate...
- Published
- 2020
9. Studies towards the total synthesis of cruentaren A and B: Stereoselective synthesis of fragments C1-C11, C12-C22 and C23-C28.
- Author
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Ganganna, Bogonda, Srihari, Pabbaraja, and Yadav, Jhillu Singh
- Subjects
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STEREOSELECTIVE reactions , *ANTINEOPLASTIC agent synthesis , *EPOXIDATION , *REGIOSELECTIVITY (Chemistry) , *ALDOL condensation - Abstract
A convergent and stereoselective approach for the synthesis of C1-C11, C12-C22, and C23-C28 fragments of cytotoxic natural products cruentaren A and B are accomplished. Highlights of the strategy include a Sharpless epoxidation followed by a regioselective opening of epoxide to generate anti and syn -stereochemistry at C9-C10 and C15-C16, an Alder-Rickert reaction between a 1,5-dimethoxy-1,4-cyclohexadiene and dienophile to construct the aromatic ring, and a lithium-mediated aldol reaction to install the C17-C18 anti -stereochemistry. The synthesis of C1-C11 and C12-C22 fragments proceed with a longest linear sequence of 10 and 17 steps from commercially available 2-butyne-1,4-diol and cis -2-butene-1,4-diol respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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10. First Stereoselective Synthesis of (6R,7R,8S)-8-Chlorogoniodiol.
- Author
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Sharada, Ambati, Rao, Kundeti Lakshmi Srinivasa, Yadav, Jhillu Singh, Rao, Tadikamalla Prabhakar, and Nagaiah, Kommu
- Subjects
- *
CHLOROHYDROCARBONS , *CHEMICAL synthesis , *STEREOSELECTIVE reactions , *CHEMICAL yield , *REGIOSELECTIVITY (Chemistry) , *EPOXIDATION - Abstract
A stereoselective synthesis of (6R,7R,8S)-8-chlorogoniodiol has been achieved in a linear sequence of 12 steps and 19.8% overall yield from cinnamyl alcohol. The key steps include Sharpless asymmetric epoxidation, regioselective ring opening of epoxide, indium-mediated Barbier allylation, and Still-Gennari olefination. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
11. Total synthesis of nafuredin B
- Author
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Gour Hari Mandal, Rajib Kumar Goswami, and Dhiman Saha
- Subjects
Sharpless epoxidation ,Olefin fiber ,Molecular Structure ,010405 organic chemistry ,Stereochemistry ,Organic Chemistry ,Epoxide ,Total synthesis ,Alkenes ,010402 general chemistry ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Lactones ,chemistry.chemical_compound ,Ring-closing metathesis ,chemistry ,Pyrones ,Wittig reaction ,Epoxy Compounds ,Moiety ,Molecule ,Physical and Theoretical Chemistry - Abstract
Total synthesis of marine secondary metabolite nafuredin B has been achieved for the first time using a convergent strategy. Sharpless epoxidation followed by acid catalyzed epoxide opening were adopted to install the tetrasubstituted hydroxy center, whereas the iterative Julia-Kocienski olefination, Wittig olefination and HWE olefination afforded the olefin bonds. Ring closing metathesis in the presence of a free tetrasubstituted hydroxy group provided the unsaturated δ-lactone moiety. This synthetic study provided unambiguous structural confirmation of the isolated nafuredin B.
- Published
- 2020
12. 8R-Lipoxygenase-catalyzed synthesis of a prominent cis-epoxyalcohol from dihomo-γ-linolenic acid: a distinctive transformation compared with S-lipoxygenases
- Author
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Jing Jin, William E. Boeglin, Jin K. Cha, and Alan R. Brash
- Subjects
arachidonic acid ,total synthesis ,Sharpless epoxidation ,trans epoxide ,hepoxilin ,18O2 incorporation ,Biochemistry ,QD415-436 - Abstract
Conversion of fatty acid hydroperoxides to epoxyalcohols is a well known secondary reaction of lipoxygenases, described for S-specific lipoxygenases forming epoxyalcohols with a trans-epoxide configuration. Here we report on R-specific lipoxygenase synthesis of a cis-epoxyalcohol. Although arachidonic and dihomo-γ-linolenic acids are metabolized by extracts of the Caribbean coral Plexaura homomalla via 8R-lipoxygenase and allene oxide synthase activities, 20:3ω6 forms an additional prominent product, identified using UV, GC-MS, and NMR in comparison to synthetic standards as 8R,9S-cis-epoxy-10S-erythro-hydroxy-eicosa-11Z,14Z-dienoic acid. Both oxygens of 18O-labeled 8R-hydroperoxide are retained in the product, indicating a hydroperoxide isomerase activity. Recombinant allene oxide synthase formed only allene epoxide from 8R-hydroperoxy-20:3ω6, whereas two different 8R-lipoxygenases selectively produced the epoxyalcohol.A biosynthetic scheme is proposed in which a partial rotation of the reacting intermediate is required to give the observed erythro epoxyalcohol product. This characteristic and the synthesis of cis-epoxy epoxyalcohol may be a feature of R-specific lipoxygenases.
- Published
- 2012
- Full Text
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13. Mechanism of Orbital Interactions in the Sharpless Epoxidation with Ti(IV) Peroxides: A DFT Study
- Author
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H. Bernhard Schlegel and Robert D. Bach
- Subjects
chemistry.chemical_classification ,Sharpless epoxidation ,Chemistry ,Hexacoordinate ,chemistry.chemical_element ,Medicinal chemistry ,Catalysis ,chemistry.chemical_compound ,Intramolecular force ,Alkoxide ,Physical and Theoretical Chemistry ,Allyl alcohol ,Alkyl ,Titanium - Abstract
The M06-2X DFT functional has been employed to examine monomeric titanium(IV) hydroperoxo catalysts that model the individual steps in the dimeric titanium(IV)-catalyzed Sharpless reaction. This is the first example of a transition structure for titanium(IV) tert-butyl hydroperoxide-catalyzed epoxidation that describes the molecular motion required for oxygen atom transfer. These epoxidation catalysts have been examined for both bimolecular reactions with E-2-butene and the intramolecular epoxidation of allyl alcohol. The transition structure for the bimolecular peroxyacetic acid epoxidation of E-2-butene has been shown to be spiro in nature, and likewise, the intramolecular epoxidation of allyl alcohol is also nearly spiro. The significance of the O-C-C═C dihedral angle of allyl alcohol is examined for the Ti(IV) tert-butyl hydroperoxide epoxidation mechanism. Evidence is presented that supports a hexacoordinate titanium peroxo environment that exists in the dimeric form of the Sharpless catalyst. The mechanism for a 1,3-rearrangement of the alkoxide ligand in a titanium hydroperoxide to the Ti center in concert with oxygen atom transfer of the proximal oxygen to the C═C bond of the substrate is presented. The dimerization of Ti(IV)-(R,R)-diethyl tartrate-diisopropoxide and its hydrolysis have been calculated. The mechanism for rapid ligand exchange with alkyl hydroperoxides involving the Ti(O-i-Pr)4 precursor is examined to show how the active epoxidation catalyst is produced.
- Published
- 2021
14. Stereoselective Synthesis of the C(1) - C(28) Fragment of Amphidinol 3.
- Author
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Yadav, Jhillu S., Gopalarao, Yerragorla, Chandrakanth, Dandekar, and Reddy, Basi V. Subba
- Subjects
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CHEMICAL synthesis , *POLYKETIDES , *STEREOSELECTIVE reactions , *POLYOLS , *EPOXY compounds , *OLEFINATION reactions - Abstract
A stereoselective synthesis of the polyol side chain (C(1) - C(28)) of amphidinol 3 has been accomplished following Sharpless epoxidation, Crimmins aldol reaction, Jacobsen kinetic resolution, Sharpless asymmetric dihydroxylation, and our own reaction for the synthesis of a chiral allylic alcohol from an epoxy alcohol. The olefin functionality was introduced by a cross metathesis and Julia- Kocienski olefination. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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15. Total Synthesis of the 7,10-Epimer of the Proposed Structure of Amphidinolide N, Part I: Synthesis of the C1-C13 Subunit.
- Author
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Ochiai, Koji, Kuppusamy, Sankar, Yasui, Yusuke, Okano, Tsubasa, Matsumoto, Yasunobu, Gupta, Nishant R., Takahashi, Yohei, Kubota, Takaaki, Kobayashi, Jun'ichi, and Hayashi, Yujiro
- Subjects
- *
MACROLIDE antibiotics synthesis , *CHEMICAL synthesis , *ANTINEOPLASTIC antibiotics , *ALDOLS , *ESTERS - Abstract
Amphidinolide N, the structure of which has been recently revised, is a 26-membered macrolide featuring allyl epoxide and tetrahydropyran moieties with 13 chiral centers. Due to its challenging structure and extraordinary potent cytotoxicity, amphidinolide N is a highly attractive target of total synthesis. During our total synthesis studies of the 7,10-epimer of the proposed structure of amphidinolide N, we have synthesized the C1-C13 subunit enantio- and diastereoselectively. Key reactions include an l-proline catalyzed enantioselective intramolecular aldol reaction, Evans aldol reaction, Sharpless asymmetric epoxidation and Tamao-Fleming oxidation. To aid late-stage manipulations, we also developed the 4-( N-benzyloxycarbonyl- N-methylamino)butyryl group as a novel ester protective group for the C9 alcohol. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
16. Synthesis of the C1–C13 fragment of eribulin mesylate
- Author
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Jooyoung Song, In-Soo Myeong, Eunim Jung, Chang Heon Suhl, Seunghui Sin, Hyoungwook Moon, Soo Hwan Yoon, Hyunik Shin, Eunjung Ko, Kee-Young Lee, Jaehun Jung, Chang-Young Oh, Heesun Jung, Junkyu Lee, Yunkyung Jung, Wonjae Kang, Yongseo Park, Seong Take Kim, and Hyoseon Lee
- Subjects
Eribulin Mesylate ,Sharpless epoxidation ,Olefin metathesis ,010405 organic chemistry ,Fragment (computer graphics) ,Chemistry ,Stereochemistry ,Organic Chemistry ,Regioselectivity ,010402 general chemistry ,Ring (chemistry) ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Drug Discovery ,Stereoselectivity - Abstract
Synthesis of the C1–C13 fragment of eribulin mesylate has been accomplished. It features a highly stereoselective construction of a trans-dihydropyran framework using three key reactions: (1) Sharpless epoxidation, (2) regioselective ring opening, and (3) olefin metathesis.
- Published
- 2019
17. A New Formal Synthetic Route to Entecavir
- Author
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Shuangping Huang, Wang Jiwu, Sun Yongli, Xiaoji Wang, Wentao Ou, and Liu Lixia
- Subjects
Hepatitis B virus ,Sharpless epoxidation ,chemistry.chemical_classification ,Ketone ,010405 organic chemistry ,Stereochemistry ,Organic Chemistry ,Epoxide ,chemistry.chemical_element ,Entecavir ,Hepatitis B ,010402 general chemistry ,medicine.disease ,medicine.disease_cause ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Formal synthesis ,chemistry ,medicine ,Selenium ,medicine.drug - Abstract
We describe a new and straightforward approach to the formal synthesis of the hepatitis B virus inhibitor entecavir, an important hepatitis B drug, in ten steps overall. Key features of the route are a Morita–Baylis–Hillman reaction, a Sharpless asymmetric epoxidation, a reductive epoxide opening of an α,β-epoxy ketone, and a Riley selenium dioxide oxidation.
- Published
- 2019
18. Evaluation of the Katsuki–Sharpless Epoxidation Precatalysts by ESI-FTMS, CID, and IRMPD Spectroscopy
- Author
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Thiago C. Correra, Philippe Maître, André Santos Fernandes, Laboratoire de Chimie Physique D'Orsay (LCPO), and Université Paris-Sud - Paris 11 (UP11)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
chemistry.chemical_classification ,Sharpless epoxidation ,Reaction mechanism ,010304 chemical physics ,Dimer ,Infrared spectroscopy ,010402 general chemistry ,01 natural sciences ,ESPECTROSCOPIA ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,chemistry ,[CHIM.ANAL]Chemical Sciences/Analytical chemistry ,Computational chemistry ,0103 physical sciences ,[CHIM]Chemical Sciences ,Carboxylate ,Infrared multiphoton dissociation ,Physical and Theoretical Chemistry ,ComputingMilieux_MISCELLANEOUS ,Alkyl - Abstract
The Katsuki-Sharpless epoxidation reaction is one of the most recognized chiral catalytic reactions, allowing for chiral epoxides to be used as starting materials for a series of synthetic pathways. The complete understanding of this reaction mechanism depends on the identification and description of species formed from Ti(IV) alkoxides and alkyl tartrates precatalysts. Despite previous reports on the nature of a bimetallic catalyst based on IR spectroscopy and NMR analysis, some debate remains. Therefore, we carried out mass spectrometry analysis by direct extraction of the ions from the reaction media by ESI(-)-FT-ICR and evaluated the observed ions by CID and IRMPD experiments. These techniques allowed us to detect carboxylates that correlate to the species in the reaction media and to confirm the actual presence of the titanium-tartrate complexes in solution. Our IRMPD results suggest the carboxylate dimer as an asymmetric species with two tartrates coordinated to a single Ti atom, while the other Ti center is coordinated by labile alkoxydes that could be easily exchanged by the organic peroxide and the substrate, allowing the epoxidation reaction to take place.
- Published
- 2019
19. Total synthesis of pro-resolving and tissue-regenerative Protectin sulfido-conjugates.
- Author
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Rodriguez, Ana R. and Spur, Bernd W.
- Subjects
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LECTINS , *REGENERATION (Biology) , *SULFIDES , *CHEMICAL synthesis , *STEREOSPECIFICITY , *DOCOSAHEXAENOIC acid - Abstract
The stereospecific total synthesis of the pro-resolving and tissue-regenerative Protectin sulfido-conjugates: 16 R ,17 S -PCTR1, 16 R ,17 S -PCTR2, and 16 R ,17 S -PCTR3, derived from docosahexaenoic acid, has been achieved. The key intermediate 16 S ,17 S -epoxy-Protectin methyl ester was synthesized using the Sharpless catalytic asymmetric epoxidation to generate the chiral centers at C16 and C17. A Cs 2 CO 3 promoted coupling provided the skipped diyne intermediate. Wittig reactions and epoxide opening with glutathione, l -cysteinylglycine, and l -cysteine methyl ester hydrochloride, respectively, were the key steps in the synthesis. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
20. Total Synthesis of the Nonenolide Xyolide Using a Regioselective Nucleophilic Epoxide Opening Approach.
- Author
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Wadavrao, Sachin B., Ghogare, Ramesh S., and Narsaiah, A. Venkat
- Subjects
- *
REGIOSELECTIVITY (Chemistry) , *EPOXY compounds , *NUCLEOPHILIC reactions , *ORGANIC synthesis , *RING-opening reactions - Abstract
The total synthesis of the nonenolide xyolide is described as a convergent synthesis in 16 steps from the commercially available starting material butane-1,4-diol. The key reactions involved are: Sharpless asymmetric epoxidation, Pinnick oxidation, acid-mediated nucleophilic regioselective epoxide ring opening, Steglich esterification, and ring-closing metathesis. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
21. Zakotvené katalyzátory pro enantioselektivní reakce na aktivovaných dvojných vazbách
- Author
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Jambor, Roman, Soural, Miroslav, Bartáček, Jan, Jambor, Roman, Soural, Miroslav, and Bartáček, Jan
- Abstract
Byla studována katalytická aktivita připravených botnavých perlových kopolymerů založených na ethyl-(4-vinylbenzyl)-L-tartrátu pro modelovou Sharplessovu epoxidaci skořicového alkoholu. Tyto katalyzátory nebylo možné recyklovat z důvodu alkoholýzy esterové vazby a s tím spojeným vymýváním tartátového fragmentu z matrice polymeru. Proto byl navržen a připraven ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylfenyl)pentanoát a z něho odvozený botnavý perlový kopolymer. Tento kopolymer se stabilně zakotveným ketoesterem odvozeným od kyseliny L-vinné bylo možné recyklovat minimálně 4 ×, což bylo ověřeno na dvou substrátech. Dosažená enantioselektivita, výtěžky a možnosti recyklace jsou nesrovnatelně vyšší ve srovnání s dosud publikovanými heterogenními systémy a jsou zcela srovnatelné s provedením reakce v homogenním prostředí. Ve druhé části práce byla zpracována literární rešerše palladiem katalyzovaných asymetrických 1,4-adic arylboronových kyselin na konjugované cyklické enony. Následně byl navržen a připraven monomer (S)-4-(terc-butyl)-2-(4-(4-vinylfenyl)pyridin-2-yl)-4,5-dihydrooxazol a z něho byly připraveny botnavé perlové kopolymery s rozdílnými síťovadly. Katalytické vlastnosti palladnatých komplexů, od připravených kopolymerů, byly studovány na adici fenylboronové kyseliny na 3-methylcyklohex-2-en-1-on. Byl diskutován vliv struktury síťovadla na katalytické vlastnosti. Katalyzátory bylo možné recyklovat až 6× a jejich účinnost byla srovnatelná s homogenním prostředím, a to i pro další modelové substráty., Catalytic activity of the prepared swellable pearl-like copolymers of ethyl-(4-vinylbenzyl)-Ltartrate was tested on the model epoxidation of cinnamyl alcohol. Recyclization of such catalysts was not possible because of tartrate leaching due to ester bond alcoholysis. On that ground, ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate and its swellable pearl-like copolymer were designed and prepared. It was possible to use this copolymer with stable-bonded ketoester derived from L-tartaric acid at least 4 times. This was tested on two substrates. The results obtained in term of yields, enantioselectivity and recyclability are superior to all currently known heterogeneous systems and fully comparable with homogeneous conditions. In the second part of this work, a literature review on palladium catalysed asymmetric 1,4-addition of arylboronic acids to conjugated cyclic enones was compiled. Consequently a new monomer (S)-4-(tert-butyl)-2-(4-(4-vinylphenyl)pyridin-2-yl)-4,5- dihydrooxazole and its swellable pearl-like copolymers with different cross-linkers were designed and prepared. Catalytic activity of palladium(II) complexes of the prepared copolymers was tested on addition of phenylboronic acid to 3-methyl-2-cyclohexenone. The relationship between the structure of the cross-linker and catalytic activity was described. It was possible to use those catalysts at least 6 times and their catalytic activity was comparable with homogenous conditions even for other substrates., Fakulta chemicko-technologická, Dokončená práce s úspěšnou obhajobou
- Published
- 2020
22. Recoverable polystyrene-supported catalysts for Sharpless allylic alcohols epoxidations
- Author
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Bartáček, Jan, Drabina, Pavel, Váňa, Jiří, Sedlák, Miloš, Bartáček, Jan, Drabina, Pavel, Váňa, Jiří, and Sedlák, Miloš
- Abstract
In this work, new heterogeneous catalysts intended for enantioselective Sharpless epoxidation were prepared. The catalysts are based on Ti(IV) complexes of cross-linked swellable spherical copolymer beads of styrene with ethyl-(4-vinylbenzyl)-L-tartrate, or with ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate. These catalysts were tested in epoxidation of cinnamyl alcohols. High conversion (up to 99%) and high enantioselectivity (up to 99% ee) were achieved in the case of catalysts based on copolymers of styrene with ethyl-(4-vinylbenzyl)-L-tartrate (5, 20, 50%). Unfortunately, the copolymers lost their enantioselectivity due to the leaching of L-tartrate, caused by alcoholysis of ester bond. This problem has been overcome by replacing the ester bond by a stable keto bond. The prepared catalyst based on the copolymer of styrene with ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate (20%) achieved a similarly high conversion and enantioselectivity as in the previous case (up to 99%, up to 99% ee) and was successfully recycled., V této práci je popsána syntéza nového heterogenního katalyzátoru určeného pro enantioselektivní Sharplessovu oxidaci. Katalyzátory jsou na bázi Ti(IV) komplexů xxxx styrenu s ethyl-(4-vinylbenzyl)-L-tartrátu nebo s ethyl-(2R, 3R)-2,3-dihydroxy-4-oxo-5-(4-vinylfenyl)pentanoátu. Byly testovány při epoxidaci skořicových alkoholů. V případě katalyzátoru na bázi kopolymeru styrenu s ethyl-(4-vinylbenzyl)-L-tartrátem (5, 20, 50%) bylo dosaženo vysoké konverze (až 99%) i vysoké enantioselektivity (až 99% ee). Bohužel kopolymery ztrácejí enantioselektivitu díky vylučování L-tartrátu, která je způsobena alkoholýzou esterové vazby. Tento problém jsme překonali nahrazením esterové vazby stabilní ketonem. Katalyzátor na bázi kopolymeru styrenu s ethyl-(2R, 3R)-2,3-dihydroxy-4-oxo-5-(4-vinylfenyl)pentanoátem (20%) dosáhl podobně vysoké konverze a enantioselektivity jako předchozí katalyzátor (až 99%, až 99% ee) a byl také úspěšně recyklován.
- Published
- 2020
23. Efficient Polymer-Supported Sharpless Alkene Epoxidation Catalyst
- Author
-
David C. Sherrington, Osmo E.O. Hormi, and Jaana K. Karjalainen
- Subjects
Asymmetric epoxidation ,Sharpless epoxidation ,polymer-supported catalyst ,Organic chemistry ,QD241-441 - Abstract
Homogeneous linear poly(tartrate ester) ligands provide high chemical yields and enantiomeric excesses in the epoxidation of trans-hex-2-en-1-ol using Ti(OPri)4-tert-butyl hydroperoxide. Branched poly(tartrate ester) can be use as heterogeneous ligands in the epoxidation of trans-hex-2-en-1-ol using Ti(OPri)4-tert-butyl hydroperoxide. Removal and recovery of the polymer catalyst is a simple filtration at the end of reactions.
- Published
- 1998
- Full Text
- View/download PDF
24. A three-step total synthesis of goniothalesdiol A using a one-pot Sharpless epoxidation/regioselective epoxide ring-opening.
- Author
-
Ramesh, Perla and Reddy, Yarram Narasimha
- Subjects
- *
EPOXIDATION , *REGIOSELECTIVITY (Chemistry) , *EPOXY compounds , *CHEMICAL synthesis , *RING-opening reactions - Abstract
Using a one-pot Sharpless asymmetric epoxidation/regioselective epoxide ring-opening as a key step, the protecting-group-free total synthesis of goniothalesdiol A was accomplished in only three steps starting from commercially available trans -cinnamaldehyde in 55.1% overall yield. In 6 previously reported total syntheses, 6–11 steps were required. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
25. Stereoselective synthesis of tetrahydropyran–tetrahydrofuran (THP–THF) core of (+)-muconin via Prins cyclization.
- Author
-
Yadav, J.S., Reddy, U.V. Subba, and Reddy, B.V. Subba
- Subjects
- *
ASYMMETRIC synthesis , *TETRAHYDROPYRANYL compounds , *TETRAHYDROFURAN , *POLYMERIZATION , *RING formation (Chemistry) , *EPOXIDATION , *OLEFINATION reactions , *PRINS reaction - Abstract
Abstract: A stereoselective synthesis of tetrahydropyran–tetrahydrofuran (THP–THF) core 2 of (+)-muconin (1) has been achieved using Prins cyclization as a key step to construct tetrahydropyran moiety. Other important transformations such as Wittig olefination, Sharpless epoxidation, regio-, and stereoselective exo-cyclization of the epoxy alcohol, titanocene induced regioselective deoxygenation of 2,3-epoxy alcohol, Grignard reaction, and Barton–McCombie reaction are successfully employed to accomplish the synthesis of THP–THF core 2. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
26. Olefin Cross-Metathesis: Studies towards the Total Synthesis of (+)-Bitungolide F.
- Author
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Dayaker, Gandrath and Krishna, Palakodety Radha
- Subjects
- *
STEREOSELECTIVE reactions , *CHEMICAL synthesis , *PYRAN synthesis , *ALKENES , *OLEFINATION reactions - Abstract
A stereoselective synthesis of (5 S,6 S)-6-[(2 S,5 S,7 R,8 E,10 E)-5-(benzyloxy)-7-{[( tert-butyl)dimethylsilyl]oxy}-11-phenylundeca-8,10-dien-2-yl]-5-ethyl-5,6-dihydro-2 H-pyran-2-one (=(+)-9- O-benzyl-11- O-[( tert-butyl)dimethylsilyl]bitungolide F) is reported. The strategy involves Gilman reaction, olefin cross-metathesis, and HornerWadsworthEmmons olefination as key steps. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
27. Stereoselective total synthesis of (+)-Cephalosporolide D.
- Author
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Rajeshwari, M. and Sharada, L. N.
- Subjects
- *
STEREOSELECTIVE reactions , *LACTONES , *ORGANIC synthesis , *PROPYLENE oxide , *EPOXIDATION , *DRUG synthesis , *DRUG accessibility - Abstract
An efficient stereoselective total synthesis of (+)-Cephalosporolide D (2) from commercially available and inexpensive starting material, (±)- propylene epoxide, is described. The key steps involved in this synthesis are Sharpless epoxidation and Yamaguchi macrolactonization as key steps. [ABSTRACT FROM AUTHOR]
- Published
- 2014
28. Origin of Enantioselectivity: A Model Study of Sharpless Epoxidation
- Author
-
Nabanita Paul
- Subjects
Sharpless epoxidation ,Chiral auxiliary ,chemistry.chemical_compound ,chemistry ,Enantioselective synthesis ,Epoxide ,Enantiomer ,Enantiomeric excess ,Combinatorial chemistry ,Racemization ,Kinetic resolution - Abstract
An enantiomerically pure substance has paramount physiological importance. Synthetic chemists aimed to produce drug molecules primarily target to synthesize pure enantiomer. Enantiomers are optically active stereoisomers so in order to accomplish products with high enantiomeric excess, asymmetric synthesis must be designed judiciously. Mimicking nature’s selective aptitude of biosynthesis is always considered a crucial challenge for synthetic chemists. The main target of drug designing is to attain skill in this specialized section. Racemization during asymmetric synthesis occasionally disappoints synthetic chemists by widely disrupting biophysical, biochemical characteristics of the synthesized compound. Kinetic resolution, however, is able to separate two enantiomers. Among innumerable synthesis, only a few are found to be associated with high enantiomeric excess yield. Contribution of enantioselective epoxide synthesis by Sharpless epoxidation is no less important in drug industry. Most striking feature of Sharpless epoxidation is materials used for producing enantiospecific epoxide are inexpensive. Product spread consisting of one predominating chiral epoxide is efficiently resolved. The current communication is aimed to analyse Sharpless epoxidation from analytical angle of a chemist using a model study of transition state structure using DIPT as chiral auxiliary and drives to find the underlying basis responsible for channelizing only one enantiomer at the suppression of other.
- Published
- 2020
29. Exploring the Mechanism of Catalysis with the Unified Reaction Valley Approach (URVA)—A Review
- Author
-
Elfi Kraka, Wenli Zou, Yunwen Tao, and Marek Freindorf
- Subjects
Sharpless epoxidation ,Allylic rearrangement ,Materials science ,unified reaction valley approach ,lcsh:Chemical technology ,010402 general chemistry ,Curvature ,01 natural sciences ,Chemical reaction ,Catalysis ,Bacillus subtilis chorismate mutase catalyzed Claisen rearrangement ,lcsh:Chemistry ,symbols.namesake ,reaction phases and reaction path curvature ,Molecule ,lcsh:TP1-1185 ,Physical and Theoretical Chemistry ,Au(I) assisted [3,3]-sigmatropic rearrangements ,Sharpless epoxidation of allylic alcohols ,010405 organic chemistry ,reaction path Hamiltonian ,vibrational spectroscopy ,0104 chemical sciences ,lcsh:QD1-999 ,Chemical physics ,Rh catalyzed methanol carbonylation ,Potential energy surface ,symbols ,van der Waals force - Abstract
The unified reaction valley approach (URVA) differs from mainstream mechanistic studies, as it describes a chemical reaction via the reaction path and the surrounding reaction valley on the potential energy surface from the van der Waals region to the transition state and far out into the exit channel, where the products are located. The key feature of URVA is the focus on the curving of the reaction path. Moving along the reaction path, any electronic structure change of the reacting molecules is registered by a change in their normal vibrational modes and their coupling with the path, which recovers the curvature of the reaction path. This leads to a unique curvature profile for each chemical reaction with curvature minima reflecting minimal change and curvature maxima, the location of important chemical events such as bond breaking/forming, charge polarization and transfer, rehybridization, etc. A unique decomposition of the path curvature into internal coordinate components provides comprehensive insights into the origins of the chemical changes taking place. After presenting the theoretical background of URVA, we discuss its application to four diverse catalytic processes: (i) the Rh catalyzed methanol carbonylation&mdash, the Monsanto process, (ii) the Sharpless epoxidation of allylic alcohols&mdash, transition to heterogenous catalysis, (iii) Au(I) assisted [3,3]-sigmatropic rearrangement of allyl acetate, and (iv) the Bacillus subtilis chorismate mutase catalyzed Claisen rearrangement&mdash, and show how URVA leads to a new protocol for fine-tuning of existing catalysts and the design of new efficient and eco-friendly catalysts. At the end of this article the pURVA software is introduced. The overall goal of this article is to introduce to the chemical community a new protocol for fine-tuning existing catalytic reactions while aiding in the design of modern and environmentally friendly catalysts.
- Published
- 2020
- Full Text
- View/download PDF
30. Synthesis of B-ring-fluorinated (-)-epicatechin gallate derivatives
- Author
-
Carina S. Michaelis, Constantin Czekelius, David D. S. Thieltges, and Kai D. Baumgarten
- Subjects
Sharpless epoxidation ,Chemistry ,Organic Chemistry ,Epoxide ,Catechin ,Optically active ,Ring (chemistry) ,Biochemistry ,chemistry.chemical_compound ,Epicatechin gallate ,Bromide ,Organic chemistry ,Chromane ,Physical and Theoretical Chemistry - Abstract
The synthesis of enantiomerically pure B-ring fluorinated catechin derivatives is presented. In a convergent approach the chromane was obtained by reaction of a lithiated fluoro-resorcine with an optically active epoxide. The latter was prepared from 3,4-difluorobenzaldehyde by reaction with vinylmagnesium bromide followed by Sharpless epoxidation. The protocol provides access to both fluorinated catechin as well as epicatechin derivatives.
- Published
- 2020
31. Stereoselective Total Synthesis of the Non-Contiguous Polyketide Natural Product (-)-Dolabriferol
- Author
-
Srihari Pabbaraja, Naresh Gantasala, and Suresh Borra
- Subjects
Sharpless epoxidation ,Natural product ,010405 organic chemistry ,Chemistry ,Stereochemistry ,Organic Chemistry ,Total synthesis ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Polyketide ,chemistry.chemical_compound ,Aldol reaction ,Dolabriferol ,Stereoselectivity ,Physical and Theoretical Chemistry ,Yamaguchi esterification - Published
- 2018
32. New chiral amino alcohol ligands for catalytic enantioselective addition of diethylzincs to aldehydes
- Author
-
Carla Sappino, Mauro Moliterno, Alessandra Mari, Alessandra Ricelli, Lorenza Suber, Giuliana Righi, Matteo Palagri, Chiara Tatangelo, Paolo Bovicelli, and Agnese Mantineo
- Subjects
Sharpless epoxidation ,diethylzinc ,010405 organic chemistry ,Chemistry ,organic chemicals ,Organic Chemistry ,amino alcohol ,Enantioselective synthesis ,asymmetric catalysis ,Alcohol ,Diethylzinc ,010402 general chemistry ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Catalysis ,Benzaldehyde ,chemistry.chemical_compound ,Benzyl alcohol ,ASYMMETRIC CATALYSIS ,NOBEL LECTURE ,DIALKYLZINCS ,AUXILIARIES ,REAGENTS ,Organic chemistry ,Physical and Theoretical Chemistry ,Chirality (chemistry) - Abstract
A study aimed at the synthesis and structure optimization of new, efficient, optically active β-amino alcohol ligands with a structure suitable for immobilization on magnetite nanoparticles has been carried out. The optimized homogeneous amino alcohol catalysts 13a and 13b, the chirality of which arises from the Sharpless epoxidation of suitable allyl alcohols, were tested by employing the well-established enantioselective amino alcohol-promoted addition of diethylzinc to benzaldehyde, giving the corresponding benzyl alcohol with nearly quantitative yield and ee = 95%. Then, their broad applicability as chiral catalysts was evaluated by carrying out the same reaction on a family of aldehydes, including variously substituted aromatic ones as well as an aliphatic analogue. The results have confirmed the validity of the fine-tuning process performed on ligands 13a and 13b. In fact, both exhibited excellent catalytic activity as demonstrated by the chemical yields and ee obtained from all the tested aldehydes, almost independent of the position and type of substitution in the aromatic ring.
- Published
- 2018
33. Concise Stereoselective Total Synthesis of (+)-Mueggelone.
- Author
-
Kumar, DachepallyAravind and Meshram, HarshadasMitaram
- Subjects
- *
STEREOSELECTIVE reactions , *EPOXIDATION , *METATHESIS reactions , *APHANIZOMENON , *FISH embryos , *FISH larvae , *FISH mortality - Published
- 2013
- Full Text
- View/download PDF
34. Stereoselective Total Synthesis of Multiplolide A and of a Diastereoisomer.
- Author
-
Reddy, Bandi Chennakesava, Bangade, Vikas Madhukar, Ramesh, Palakuri, and Meshram, Harshadas Mitaram
- Subjects
- *
DIASTEREOISOMERS synthesis , *OPTICAL isomers , *JACOBSEN reaction , *CHEMICAL reactions , *EPOXIDATION , *METATHESIS reactions - Abstract
A stereoselective total synthesis of multiplolide A ( 1) and of its diastereoisomer 2 was described from easily accessible starting materials ( Schemes 2- 4). The synthetic strategy involves a Jacobsen resolution, Sharpless epoxidation, Swern oxidation, Yamaguchi reaction, and ring-closing metathesis (RCM). [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
35. The First Stereoselective Total Synthesis of Naturally Occurring, Bioactive (3 R,5 R)-1-(4-Hydroxyphenyl)-7-phenylheptane-3,5-diol and the Synthesis of Its Enantiomer.
- Author
-
Reddy, Parigi Raghavendar, Sudhakar, Chithaluri, Kumar, Jayprakash Narayan, and Das, Biswanath
- Subjects
- *
STEREOSELECTIVE reactions , *STEREOCHEMISTRY , *STERIC hindrance , *EMETICS , *EPOXIDATION , *ENANTIOMERS - Abstract
The first stereoselective total synthesis of the naturally occurring anti-emetic diarylheptanoid (3 R,5 R)-1-(4-hydroxyphenyl)-7-phenylheptane-3,5-diol ( 1) was accomplished starting from 4-hydroxybenzaldehyde and involving a Sharpless kinetic resolution and an asymmetric epoxidation as the key steps ( Scheme 2). The enantiomer 1a of this compound was also simultaneously prepared. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
36. Total Synthesis and Stereochemical Assignment of (-)-Zenkequinone B.
- Author
-
Vanga, Devendar G. and Kaliappan, Krishna P.
- Subjects
- *
CHEMICAL synthesis , *AROMATIZATION , *TARTARIC acid , *DIELS-Alder reaction , *CHEMICAL reactions - Abstract
The first enantioselective total synthesis and a concise racemic synthesis of zenkequinone B are reported here by utilizing a sequential enyne metathesis, Diels-Alder and aromatization reactions. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
37. The first total synthesis of (−)-bitungolide E
- Author
-
Shashidhar, J., Mahender Reddy, K., and Ghosh, Subhash
- Subjects
- *
ALKYLATION , *METATHESIS reactions , *ASYMMETRY (Chemistry) , *PHOSPHATASES , *CHEMICAL reactions , *ORGANIC synthesis - Abstract
Abstract: The first total synthesis of (−)-bitungolide E is described. The key steps include a Myers’ alkylation, modified Evans’ syn aldol-reaction, using Crimmins protocol, Sharpless asymmetric epoxidation and ring-closing metathesis reaction. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
38. Stereoselective total synthesis of (+)-anamarine via cross-metathesis protocol
- Author
-
Sabitha, Gowravaram, Reddy, C. Nagendra, Gopal, Peddabuddi, and Yadav, J.S.
- Subjects
- *
ASYMMETRIC synthesis , *PYRAN , *METATHESIS reactions , *ETHYLENE glycol , *LACTONES , *OXIDATION , *HYDROXYLATION , *ALUMINUM - Abstract
Abstract: A convergent stereoselective total synthesis of (+)-anamarine via cross-metathesis (CM) protocol starting from 2-butyn-1,4-diol and vinyl lactone is reported. Other key features of the strategy include the use of Sharpless asymmetric epoxidation, Sharpless dihydroxylation, and Red-Al reduction. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
39. First stereoselective synthesis of synargentolide A and revision of absolute stereochemistry
- Author
-
Sabitha, Gowravaram, Gopal, Peddabuddi, Reddy, C. Nagendra, and Yadav, J.S.
- Subjects
- *
LACTONES , *ETHER (Anesthetic) , *ORGANIC synthesis , *ASYMMETRY (Chemistry) , *STEREOCHEMISTRY , *OXIDATION , *METATHESIS reactions - Abstract
Abstract: The first stereoselective total synthesis of synargentolide A isolated from Syncolostemon argenteus has been achieved from commercially available (R)-benzyl glycidyl ether using Sharpless asymmetric epoxidation and cross-metathesis reactions as the key steps. Comparing the spectral data of the synthesized and naturally occurring synargentolide A, the C4′ and C6′- stereogenic centers of the natural synargentolide A were assigned a corrected anti relationship. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
40. Synthetic studies toward 1,2-dioxanes as precursors of potential endoperoxide-containing antimalarials
- Author
-
Gemma, Sandra, Martí, Francesc, Gabellieri, Emanuele, Campiani, Giuseppe, Novellino, Ettore, and Butini, Stefania
- Subjects
- *
DIOXANE , *PEROXIDES , *ANTIMALARIALS , *ARTEMISININ , *MALARIA treatment , *ORGANIC synthesis - Abstract
Abstract: Introduction in therapy of the naturally occurring trioxane artemisinin opened a new era in malaria treatment and prompted the development of semisynthetic and synthetic derivatives characterized by the presence of the key peroxide bridge. The 1,2-dioxane ring is present in some natural endoperoxides such as plakortin and dihydroplakortin, which are endowed with interesting antimalarial properties. Here we describe the development of a versatile stereocontrolled synthetic strategy to 1,2-dioxanes functionalized at the critical C3, C4, and C6 positions, potentially useful for the development of innovative antimalarials. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
41. Total synthesis of (−)-baconipyrone C
- Author
-
Yadav, J.S., Sathaiah, K., and Srinivas, R.
- Subjects
- *
ASYMMETRIC synthesis , *METHYL groups , *RESOLUTION (Chemistry) , *PROPIONATES , *CHEMICAL synthesis , *ENZYMES , *STEREOCHEMISTRY , *EPOXY compounds - Abstract
Abstract: A highly stereoselective asymmetric total synthesis of marine polypropionate (−)-baconipyrone C has been achieved. Utilization of desymmetrization technique to create five stereogenic centres, Sharpless epoxidation, Gilman''s reaction and resolution of methyl group using enzyme PS-C is the highlight of the synthesis. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
42. The epoxidation of allyl alcohol on Ti-complex/MCM-48 catalyst
- Author
-
Zhao, Wei, Hao, Zhengping, Hu, Chun, Li, Jinjun, and Xu, Xiuyan
- Subjects
- *
ALCOHOL , *DRUGS , *ALCOHOLS (Chemical class) , *ALCOHOLIC beverages , *DRUGS of abuse - Abstract
Abstract: The heterogeneous sharpless-type catalyst was prepared by an in situ method using MCM-48 as the support. The influence of the incorporation process on the structure of MCM-48 was studied by the XRD, FT-IR, 29Si MASNMR and N2 adsorption–desorption. The obtained materials showed the definite catalytic activity on the epoxidation of allyl alcohol under the system of acetone (solvent) and peroxycarbamide (oxidant). [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
43. Studies on radical cyclization of 2,3-epoxy alcohols containing a β-(alkoxy)acrylate moiety using Cp2TiCl
- Author
-
Chakraborty, Tushar Kanti, Samanta, Rajarshi, and Ravikumar, Krishnan
- Subjects
- *
ORGANIC chemistry , *PHYSICAL sciences , *CHEMISTRY , *SCIENCE - Abstract
Abstract: Radical-mediated opening of chiral 2,3-epoxy alcohols, containing suitably positioned β-(alkoxy)acrylate moieties, using Cp2TiCl triggered intramolecular cyclization to give tetrahydrofuran and tetrahydropyran moieties. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
44. Synthesis and NMR experiments of (4,5,6-13C)-deoxymannojirimycin. A new entry to 13C-labeled glycosidase inhibitors
- Author
-
Murruzzu, Caterina, Alonso, Mònica, Canales, Angeles, Jiménez-Barbero, Jesus, and Riera, Antoni
- Subjects
- *
CARRIER proteins , *NUCLEAR magnetic resonance , *METATHESIS reactions , *CHEMICAL reactions - Abstract
Abstract: The synthesis of (4,5,6-13C)-deoxymannojirimycin is described. The route employed is based on Sharpless asymmetric epoxidation of (1,2,3-13C)(E)-2,4-pentadien-1-ol and uses ring-closing metathesis as a key step. The labeled compound may be easily used for protein-binding experiments using NMR spectroscopic methods. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
45. Pasteur -- The Harbinger of Stereochemistry.
- Author
-
Nagendrappa, Gopalpur
- Subjects
ENANTIOMERS ,TARTARIC acid ,OPTICAL properties ,STEREOCHEMISTRY ,TETRAHEDRAL coordinates ,ORGANIC compounds - Abstract
Twenty five years before the tetrahedral structure for carbon was proposed in 1874 to explain the optical activity and other properties of organic compounds, Louis Pasteur discovered the existence of enantiomerism in tartaric acid. He separated the oppositely shaped crystals of tartaric acid by handpicking, found their optical rotation to be in opposite directions, and concluded that this optical property was attributable to the existence of two oppositely shaped tartaric acid molecules. Thus the new subject of stereochemistry was heralded. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
46. Total Syntheses of Disorazoles A1 and B1 and Full Structural Elucidation of Disorazole B1
- Author
-
Kiran Kumar Pulukuri, Marek Buchman, Kyriacos C. Nicolaou, and Gabriel Bellavance
- Subjects
Sharpless epoxidation ,010405 organic chemistry ,Chemistry ,Stereochemistry ,Enantioselective synthesis ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Stannane ,Catalysis ,0104 chemical sciences ,Stille reaction ,Kinetic resolution ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Suzuki reaction ,Wittig reaction ,Yamaguchi esterification - Abstract
Described herein are the first total syntheses of naturally occurring antitumor agents disorazoles A1 and B1 and the full structural assignment of the latter. The syntheses were achieved through convergent strategies employing enantioselective constructions of the required building blocks, including a novel Sharpless epoxidation/enzymatic kinetic resolution of stannane-containing substrates that led selectively to both enantiomeric forms of an epoxy vinyl stannane, and a series of coupling reactions, including a Wittig reaction, a Suzuki coupling, a Stille coupling, a Yamaguchi esterification and a Yamaguchi macrolactonization.
- Published
- 2017
47. Studies towards the total synthesis of cruentaren A and B: Stereoselective synthesis of fragments C1-C11, C12-C22 and C23-C28
- Author
-
Bogonda Ganganna, Pabbaraja Srihari, and Jhillu S. Yadav
- Subjects
Sharpless epoxidation ,010405 organic chemistry ,Stereochemistry ,Chemistry ,Longest linear sequence ,Organic Chemistry ,Regioselectivity ,Epoxide ,Total synthesis ,010402 general chemistry ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,chemistry.chemical_compound ,Aldol reaction ,Cruentaren ,Drug Discovery ,Stereoselectivity - Abstract
A convergent and stereoselective approach for the synthesis of C1-C11, C12-C22, and C23-C28 fragments of cytotoxic natural products cruentaren A and B are accomplished. Highlights of the strategy include a Sharpless epoxidation followed by a regioselective opening of epoxide to generate anti and syn -stereochemistry at C9-C10 and C15-C16, an Alder-Rickert reaction between a 1,5-dimethoxy-1,4-cyclohexadiene and dienophile to construct the aromatic ring, and a lithium-mediated aldol reaction to install the C17-C18 anti -stereochemistry. The synthesis of C1-C11 and C12-C22 fragments proceed with a longest linear sequence of 10 and 17 steps from commercially available 2-butyne-1,4-diol and cis -2-butene-1,4-diol respectively.
- Published
- 2017
48. Reductive opening of glycal derived highly functionalized 2,3-epoxy-1-iodides with zinc dust: an efficient method for the synthesis of acyclic long chain polyhydroxylated terminal alkenic alcohols
- Author
-
Reddy, L. Vijaya Raghava, Sagar, Ram, and Shaw, Arun K.
- Subjects
- *
ALCOHOL , *REACTION time , *ZINC , *DRUGS - Abstract
Abstract: The synthesis of densely functionalized acyclic long chain terminal alkenic alcohols was achieved by reductive opening of glycal derived 2,3-epoxy-1-iodides, with commercial zinc dust alone in a short reaction time with excellent yields involving a simple reaction procedure and easy work-up. A mechanism involving an organometallic intermediate is proposed. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
49. Stereoselective Synthesis of Anti-Hepatitis B Drug, Entecavir, through Regio- and Stereoselective Epoxide Cleavage
- Author
-
Lak Shin Jeong, Hong Rae Kim, Yongseok Choi, and Young Eum Hyun
- Subjects
Sharpless epoxidation ,Drug ,010405 organic chemistry ,Chemistry ,Stereochemistry ,media_common.quotation_subject ,Organic Chemistry ,Epoxide ,Regioselectivity ,Entecavir ,Hepatitis B ,010402 general chemistry ,medicine.disease ,Cleavage (embryo) ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,medicine ,Stereoselectivity ,medicine.drug ,media_common - Abstract
A stereoselective synthesis of entecavir, an anti-hepatitis B (HBV) drug, was accomplished by a regioselective isopropylidene cleavage, stereoselective Sharpless epoxidation, and TiIII-mediated regio- and stereoselective epoxide cleavage as key steps.
- Published
- 2017
50. Total syntheses of 9-epoxyfalcarindiol and its diastereomer
- Author
-
Mingan Wang, Kaijie Ji, Yanli Huang, Yun Zhou, Qinghua Bian, Yan-Qing Yang, Pengfei Yang, Jiangchun Zhong, Jingwei Yin, Ning Ye, Shuoning Li, Min Wang, and Lifeng Wang
- Subjects
Sharpless epoxidation ,chemistry.chemical_classification ,010405 organic chemistry ,Organic Chemistry ,Acrolein ,Enantioselective synthesis ,Diastereomer ,Alcohol ,Tartrate ,010402 general chemistry ,01 natural sciences ,Aldehyde ,Catalysis ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Organic chemistry ,Physical and Theoretical Chemistry - Abstract
The first total syntheses of 9-epoxyfalcarindiol 1a and its diastereomer 1b have been achieved. Central to our approach were the Zn-cyclopropane-based amino alcohol catalyzed enantioselective alkynylation of acrolein, the diastereoselective addition of a diynic ester to an epoxy aldehyde, and the asymmetric Sharpless epoxidation of allylic alcohol catalyzed with L-(+)-diethyl tartrate and Ti(OiPr)4.
- Published
- 2017
Catalog
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