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A substituted bishomocubane structure colloquially known as a Thiele cage was previously observed to undergo an alkyl-extended pinacol-type rearrangement, wherein 1,2-aryl migration and ketone formation occurred together with (or at least in close succession to) opening of a strained cyclobutane bond. While there was some indication that the rearrangement reaction might proceed via a stepwise process involving a sequence of carbocation intermediates, previous studies did not uncover any direct evidence for the formation of carbocations, and did not fully explain the regio- and stereospecificity of the reaction. Here we describe the isolation and detailed characterization of a second rearrangement product formed under the pinacol reaction conditions, the existence of which implicates the formation of discrete carbocation intermediates along the reaction pathway. Observation of this new product also finally explains the fate of any Thiele cage material that is converted to a carbocation, but which is not geometrically predisposed to react through a facile 1,2-aryl migration. As such, our findings resolve previous questions surrounding the origin of regio- and stereospecificity in the alkyl-extended pinacol rearrangement. [ABSTRACT FROM AUTHOR]

Layered Ti3C2Tx MXene has been successfully intercalated and exfoliated with the simultaneous generation of a 3D silica network by treating its cationic surfactant intercalation compound (MXene-CTAB) with an alkoxysilane (TMOS), resulting in a MXene–silica nanoarchitecture, which has high porosity and specific surface area, together with the intrinsic properties of MXene (e.g., photothermal response). The ability of these innovative MXene silica materials to induce thermal activation reactions of previously adsorbed compounds is demonstrated here using NIR laser irradiation. For this purpose, the pinacol rearrangement reaction has been selected as a first model example, testing the effectiveness of NIR laser-assisted photothermal irradiation in these processes. This work shows that Ti3C2Tx-based nanoarchitectures open new avenues for applications that rely on the combined properties inherent to their integrated nanocomponents, which could be extended to the broader MXene family. [ABSTRACT FROM AUTHOR]

Pinacol rearrangement is an important topic in undergraduate organic chemistry courses, but students often struggle to fully understand and grasp the rearrangement mechanism, regioselectivity and group migration aptitude. In order to enhance students' comprehension of pinacol rearrangement reactions, we design an experiment that utilizes computational chemistry methods to address organic chemistry problems. Through intuitive visuals and specific data, the experiment clearly demonstrates that substrates capable of forming stable carbocation intermediates primarily undergo stepwise rearrangement mechanisms, while those unable to form stable intermediates undergo concerted rearrangement mechanisms. The computational results validate that the regioselectivity of the reaction depends on the protonation site of the neighboring diol hydroxyl group and the group migration ability, and it unequivocally establishes the order of group migration ability as hydrogen > aromatic > alkyl. Furthermore, a rational explanation for this order is provided from a microscopic perspective. [ABSTRACT FROM AUTHOR]

4‐Aryl‐1H‐isochromene derivatives have been successfully synthesized by Brønsted acid‐catalyzed pinacol rearrangement/intramolecular cyclization of the substituted 1‐(2‐(hydroxymethyl)phenyl)‐2‐arylethane‐1,2‐diols. The reaction generally proceeded with low catalyst loading of trifluoromethanesulfonic acid (5 mol%) for short reaction times (10‐20 min) to furnish the desired 4‐aryl‐1H‐isochromenes which were subsequently hydrogenated to 4‐aryl‐isochromans with up to 90 % yield. Moreover, oxidation of the resulting 4‐aryl‐isochroman provided the desired 4‐aryl‐isochroman‐1‐one in good yield. [ABSTRACT FROM AUTHOR]

A synthetic strategy involving a Simmons‐Smith cyclopropanation, followed by an acid‐catalyzed pinacol rearrangement, was developed to transform α‐hydroxy silyl enol ethers into 1‐substituted bicyclo[2.1.1]hexan‐5‐ones. These bicyclic ketones underwent further synthetic manipulations to generate various 1,5‐disubstituted bicyclo[2.1.1]hexanes, which could serve as potential bioisosteres of ortho‐substituted arenes. [ABSTRACT FROM AUTHOR]

Nardosinone, a predominant bioactive product from Nardostachys jatamansi DC, is well-known for its promising therapeutic applications, such as being used as a drug on anti-inflammatory, antidepressant, cardioprotective, anti-neuroinflammatory, anti-arrhythmic, anti-periodontitis, etc. However, its stability under varying environmental conditions and its degradation products remain unclear. In this study, four main degradation products, including two previously undescribed compounds [2–deoxokanshone M (64.23%) and 2–deoxokanshone L (1.10%)] and two known compounds [desoxo-narchinol A (2.17%) and isonardosinone (3.44%)], were firstly afforded from the refluxed products of nardosinone in boiling water; their structures were identified using an analysis of the extensive NMR and X–ray diffraction data and the simulation and comparison of electronic circular dichroism spectra. Compared with nardosinone, 2–deoxokanshone M exhibited potent vasodilatory activity without any of the significant anti-neuroinflammatory activity that nardosinone contains. Secondly, UPLC–PDA and UHPLC–DAD/Q–TOF MS analyses on the degradation patterns of nardosinone revealed that nardosinone degraded more easily under high temperatures and in simulated gastric fluid compared with the simulated intestinal fluid. A plausible degradation pathway of nardosinone was finally proposed using nardosinonediol as the initial intermediate and involved multiple chemical reactions, including peroxy ring-opening, keto–enol tautomerization, oxidation, isopropyl cleavage, and pinacol rearrangement. Our findings may supply certain guidance and scientific evidence for the quality control and reasonable application of nardosinone-related products. [ABSTRACT FROM AUTHOR]

An electrochemical method for the generation of 1,2‐diols through the reductive coupling of aldehydes has been developed, and the 1,2‐diols were used directly without separation for the pinacol rearrangement process. The electro‐organic strategy had mild reaction conditions and avoided the use of reductants. The pinacol rearrangement was controllable to access to the hydride‐migrated product 1,2‐disubstituted. The key factor in selectivity was the use of macrocyclic compound cucurbit[7]uril, which plays a key role in the interaction with aromatic ring of 1,2‐diol. On the basis of experimental results, the mechanism, include the electroreductive coupling and pinacol rearrangement process, was illustrated. [ABSTRACT FROM AUTHOR]

We report a synthetic endeavor towards the highly strained pentacyclic caged framework of the mavacuran alkaloids which culminated with the concise total synthesis of C‐fluorocurine, C‐profluorocurine, C‐mavacurine, normavacurine, 16‐epi‐pleiocarpamine and taberdivarine H. We designed a strategy involving late‐stage construction of the D ring by Michael addition of a vinylic nucleophile to a 2‐indolyl acrylate moiety. While the intramolecular Michael addition did not succeed, we were able to perform a diastereoselective unusual intermolecular 1,4‐addition of a functionalized vinyl lithium reagent to a readily accessible Michael acceptor with the assistance of the piperidine nitrogen atom through the formation of a complex as suggested by DFT computations. Final cyclization was achieved by nucleophilic substitution to form an ammonium intermediate. The first total syntheses of C‐profluorocurine and C‐fluorocurine were finalized by the dihydroxylation of C‐mavacurine and a pinacol rearrangement, respectively. [ABSTRACT FROM AUTHOR]

Finally, the alkyl nitrile radical B Int-26 e b got added to potassium metabisulfite to furnish the requisite alkyl sulfonyl radical intermediate B Int-26 f b . The alkyl radical B Int-38 c b upon intramolecular 5- I exo i -dig cyclization with cyano-group led to the formation of exocyclic imine-radical B Int-38 d b (overall 1,4-cayno shift), which upon final -fragmentation gave the ketone B 38 b b . The alkyl radical B Int-10 f b was then combined with the complex B Int-10 e b to give a new alkyl radical B Int-10 g b , which upon oxidation-semipinacol rearrangement delivered ketone B 10 d b . Keywords: Electrocatalysis; ketone; photocatalysis; polar-cross over; radical EN Electrocatalysis ketone photocatalysis polar-cross over radical 834 853 20 03/27/23 20230321 NES 230321 Semipinacol rearrangement has brought several elegant methods for the rapid synthesis of various complex scaffolds and as a result, has been applied extensively in the total synthesis of natural products. [Extracted from the article]

This article, titled "Pinacol Rearrangement of Lappaconine," discusses the synthesis and characterization of anhydrodemethanollappaconine (3), a compound derived from lappaconitine. Lappaconitine is a diterpene alkaloid with various biological activities and is used in drugs in Russia and China. The researchers aimed to increase the yield of compound 3 in order to study its potential as an antiarrhythmic. They investigated the use of different acidic reagents and confirmed the structure of compound 3 using modern spectroscopic techniques. The best yield of compound 3 was obtained using 65% CF3SO3H. The article provides detailed experimental procedures and characterization data for compound 3. [Extracted from the article]

A selective pinacol rearrangement of hydrobenzoin compounds was established through a heterogeneous catalysis strategy in the presence of cucurbit[7]uril. As an unexpected consequence, the ketone was generated as the sole product with the cucurbit[7]uril‐controlled hydride migration under optimized conditions. The five recycled runs suggested the catalytic activity of the cucurbit[7]uril remained. The experimental analysis and DFT calculation disclosed the important role of supramolecular encapsulation of substrates within the cavity of the macrocyclic host to fix the phenyl groups on hydrobenzoin compounds and trigger the hydride migration, therefore, ketone was the prior product. [ABSTRACT FROM AUTHOR]

Citrus canker, caused by Xanthomonas citri subsp. citri ( Xcc ), is a severe citrus disease. Currently, copper-containing pesticides are widely used to manage this disease, posing high risks to the environment and human health. This study reports the discovery of naturally occurring anti- Xcc compounds from a deep-sea fungus, Aspergillus terreus SCSIO 41202, and the possible mode of action. The ethyl acetate extract of A. terreus was subjected to bioassay-guided isolation, resulting in the discovery of eight anti- Xcc compounds ( 1 - 8 ) with minimum inhibitory concentrations (MICs) ranging from 0.078 to 0.625 mg/mL. The chemical structures of these eight metabolites were determined by integrative analysis of various spectroscopic data. Among these compounds, Asperporonin A ( 1 ) and Asperporonin B ( 2 ) were identified as novel compounds with a very unusual structural skeleton. The electronic circular dichroism was used to determine the absolute configurations of 1 and 2 through quantum chemical calculation. A bioconversion pathway involving pinacol rearrangement was proposed to produce the unusual compounds ( 1 - 2 ). Compound 6 exhibited an excellent anti- Xcc effect with a MIC value of 0.078 mg/mL, which was significantly more potent than the positive control CuSO 4 (MIC = 0.3125 mg/mL). Compound 6 inhibited cell growth by disrupting biofilm formation, destroying the cell membrane, and inducing the accumulation of reactive oxygen species. In vivo tests indicated that compound 6 is highly effective in controlling citrus canker disease. These results indicate that compounds 1 - 8 , especially 6 , have the potential as lead compounds for the development of new, environmentally friendly, and efficient anti- Xcc pesticides.

Reactions of both diastereomers of 1,2‐bis(4‐methoxyphenyl)cyclohexane‐1,2‐diol (1 d) with tris(2,4‐dibromo‐phenyl)aminium hexachloroantimonate as the oxidant in dichloromethane have been investigated to get evidence on the possibility that a pinacol rearrangement may be oxidatively activated rather than acid‐catalyzed. Relevant to this, we found that in the presence of an excess (4 eq) of oxidant, cis‐1 d afforded the rearrangement product 2,2‐bis(4‐methoxyphenyl)cyclohexanone in large amounts, while trans‐1 d gave exclusively the oxidative cleavage product 1,6‐bis(4‐methoxyphenyl)hexane‐1,6‐dione. Stereospecific implications explaining the reactivity difference between the two diastereomeric radical cation intermediates, cis‐ and trans‐1 d⋅+, are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a facile synthesis method of a porous ionic crystal (PIC) composed of the little-known δ-Keggin-type cationic polyoxoaluminum cluster ([δ-Al13O4(OH)24(H2O)12]7+, δ-Al13) with an oppositely-charged polyoxometalate, which enabled us to investigate the activity as a solid acid. The δ-Al13 based PIC exhibited much higher activity in pinacol rearrangement, a typical acid-catalyzed reaction, than the PIC based on the well-known and thermodynamically stable rotational isomer (ε-Al13). This work is a rare example of rotational isomers of polyoxoaluminum clusters exhibiting remarkably different catalytic activities. [ABSTRACT FROM AUTHOR]

A intermolecular nucleophilic addition/pinacol rearrangement cascade reaction of 1,2‐dicarbonyl compounds and Blaise reaction intermediates has been developed. This highly efficient transformation enables the quick construction of γ‐spiro lactams in a single operation with moderate to good yields as well as mild reaction condition. [ABSTRACT FROM AUTHOR]

• The CF 3 group effectively aids the bifunctional activation and improves catalytic activity of N-triflyphosphoramide. • The CF 3 group plays a significant role in controlling the enantioselectivity. • The CF 3 group contributing different strength multiple interactions to achieve high degree of enantioselectivity. • The P(=NTf)OH tautomer of N-triflyphosphoramide is an active catalyst form for the rearrangement reaction. The acidity of the chiral Brønsted acid catalysts is crucial for the catalytic efficiency, the highly acidic BINOL-derived chiral N-triflylphosphoramides can provide effective asymmetric catalysis for rearrangement reactions. Despite multiple interactions between the basic/acidic sites of the functional group and the substrates have been evaluated, the origin of high catalytic activity and excellent enantioselelctivity of N-triflylphosphoramides catalyst is still challenging. Especially the role of CF 3 groups in controlling activation mode and determining enantioselectivity. Thus, two effective case reactions of pinacol and acyloin rearrangement catalyzed by BINOL N-triflyphosphoramide were employed to provide basis understanding for these issues. Our calculations reveal that the P(=NTf)OH tautomer of N-triflyphosphoramide is an active catalyst form for the rearrangement reaction, differing from previous proposed model involving P(=O)NHTf group. This can be ascribed to the additional C–F··· π interaction between the CF 3 group of catalyst and the migration group of substrate in the preferred activation model. Furthermore, we found that the CF 3 substituent on the central functional group effectively aids the bifunctional activation and improves catalytic activity of N-triflyphosphoramide catalyst. More importantly, the CF 3 substituent and the orientation of migration groups play a significant role in controlling the enantioselectivity by contributing different strength multiple C–H···F, C–F··· π , and C–H··· π interactions between catalyst and substrate. Overall, our findings on the factors affecting the stereochemical control may show utility for other challenging asymmetric reactions catalyzed by chiral N-triflylphosphoramides. [ABSTRACT FROM AUTHOR]

ZrO2, Mo(VI)/ZrO2, SO4 2-/ZrO2 and Pt-SO4 2-/ZrO2 supported on honeycomb monoliths have been prepared and characterized for their physico-chemical properties such as surface acidity, crystalinity, functionality and morphology. These materials have been used as solid acid catalysts in the pinacol rearrangement of benzopinacol under microwave irradiation. A few diols have also been subjected to pinacol rearrangement to obtain a good conversion of rearrangement products with high selectivity. Optimization of reaction conditions has also studied to determine the most suitable reaction conditions for the effective synthesis of pinacolone derivatives. Up to 98% conversion of benzopinacol is observed under a set of optimized reaction conditions. A reactivation and reusability study of zirconia based solid acid catalysts has also performed. [ABSTRACT FROM AUTHOR]

The microwave pyrolysis (MWP) of sewage sludge (SS) was conducted to investigate the impact of the organic composition of SS on the yield and composition of the derived bio-oil. The experiments were conducted in a microwave oven at 900 °C with a heating rate of 50 °C/min and achieved the product yield of 43.10 ± 2.23% bio-oil, 48.07 ± 1.26% bio-char, 8.83 ± 1.65% bio-gas. The chemical composition of bio-oil was investigated using gas chromatography–mass spectrometry and 145 species were identified. Protein and lipid contents in SS are the primary source of bio-oil yield, while bio-gas are predominantly derived from lignocellulosic materials. The unique non-thermal effects of microwaves can facilitate the ring-opening of small cycloalkanes to form straight olefins through hydrogen transfer reactions. Additionally, they can promote aldol condensation reactions, Pinacol rearrangements, and methoxy cleavage to form phenolic and aromatic structures with methyl groups. Furthermore, microwaves can aid in the dehydration, condensation, and cyclization reactions of amino acids to produce N-heterocycles while also facilitating lipid depolymerization into fragments for Diels–Alder cyclization. The results of this study will be beneficial for deeply understanding reactant characteristics and the reaction process during the MWP of SS. • MWP is more effective than conventional pyrolysis for bio-oil production. • Protein and lipids in SS are the primary feedstock for bio-oil production via MWP. • Triacetonamine is the predominant constituent of bio-oil derived from MWP of SS. • The non-thermal effects of microwaves promote H transfer and Diels–Alder reactions. • The mechanism of MWP for organic components in SS is elucidated. [ABSTRACT FROM AUTHOR]

An efficient scandium(III)‐triflate‐catalyzed pinacol‐pinacolone rearrangement and cyclization of 1,2‐diaryl‐1,2‐ethanediol has been developed, providing a variety of 2,3‐dihydro‐1H‐3‐benzazepine derivatives in good yields. The obtained products could be transformed to other valuable building blocks for the synthesis of some biologically active compounds or natural products. Moreover, this protocol was also successfully employed for the synthesis of the corresponding 1‐phenyl‐3,4,5,6‐tetrahydrobenzo[d]azocine and 3‐phenylisoquinoline products. [ABSTRACT FROM AUTHOR]

Triterpene glycosides are known as characteristic metabolites of sea cucumbers (class Holothuroidea, phylum Echinodermata). The most of them have lanostane aglycones containing 18(20)-lactone, i.e. belongs to so-called holostane series. However non-holostane glycosides having no lactone (with the both normal and shortened side chains) or containing 18(16)-lactone function were also found in these invertebrates last a few decades. In addition, some very rare findings of the glycosides containing rearranged lanostane skeleton systems were reported. Probably, these natural products are formed in result of intramolecular aldol condensation of 1,6-diketo precursors as well as by Meinwald rearrangement of 1,2-epoxy precursor or pinacol-pinacolone rearrangement of fully substituted 1,2-diol precursor. Structures, biosynthesis and evolution of non-holostane aglycones of sea cucumber triterpene glycosides are discussed. Biological properties of the glycosides with hon-holostane aglycones are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we report an easy-to-prepare, cost-effective, efficient, and reusable silica-supported orthophosphoric acid (OPA) catalyst for pinacolic rearrangement. The surface properties of this catalyst were successfully characterized with the help of 31P NMR, TGA, DSC, FT-IR, titration, and microscopy. OPA, hydrogen bonded on the surface, is actually the active species and the reaction seems to occur in the liquid phase embedded in the silica support. As a consequence, the extracting solvent should be chosen with cautious to guarantee the recyclability of the catalyst. As example, pinacol rearrangement reactions were successfully realized with this catalyst and OPA/SiO2 proved to be as efficient as homogeneous orthophosphoric acid to promote the reaction of pinacol derivatives. When using dichloromethane as extracting solvent, OPA/SiO2 can be reuse up to ten times without a significant loss of activity. After ten runs, no physical damage of the catalyst has been observed by microscopy proving its suitability for such application. [ABSTRACT FROM AUTHOR]

A concise and divergent approach for the total syntheses of four cembrane diterpenoids, namely (+)‐sarcophytin, (+)‐chatancin, (−)‐3‐oxochatancin, and (−)‐pavidolide B, has been developed, and it also led to the structural revision of (−)‐isosarcophytin. The key steps of the strategy feature a double Mukaiyama Michael addition/elimination, a Helquist annulation, two substrate‐controlled facial‐selective hydrations, and a pinacol rearrangement. The described syntheses not only achieved these natural products in an efficient manner, but also provided insight into the biosynthetic relationship between the two different skeletons. Efficient access: A concise and divergent approach for the total syntheses of four cembranoids, namely (+)‐sarcophytin, (+)‐chatancin, (−)‐3‐oxochatancin, and (−)‐pavidolide B, was developed. The key features of the efficient strategy entail a double Mukaiyama–Michael addition/elimination, a Helquist annulation, two facial‐selective hydrations, and a pinacol rearrangement. [ABSTRACT FROM AUTHOR]

Among the fundamental chemical transformations in organic synthesis, rearrangement has been recognized as powerful and reliable reactions for the construction of carbon–carbon or carbon–heteroatom bonds. Benefiting from the advance of the novel catalytic system, catalyst design and activation mode, the chemistry of enantioselective rearrangements has experienced ever‐growing development recently and has been successfully used in the synthesis of chiral non‐racemic building blocks, natural products, and other valuable compounds. We present herein a survey of the recent development on the catalytic enantioselective rearrangement (from 2013 onward) organized according to the rearrangement type. Multiple H‐bondings, the association of ion pairing with H‐bonding, and anion‐binding with cation‐binding are highly rewarding approaches in the development of catalytic enantioselective rearrangements. [ABSTRACT FROM AUTHOR]

The first extended pinacol rearrangement across an sp3–sp3 bond is reported. The reaction appears to be both stereo- and regio-specific, and results in an extremely rare example of cage opening for a 1,3-bishomocubane structure derived from Thiele's ester. [ABSTRACT FROM AUTHOR]

Using 1,1,2‐triphenylethane‐1,2‐diol, AgSbF6, and NOSbF6, two different carbonyl products of rearrangement were synthesized: neutral ketone compound 1,2,2‐triphenylethanone (1) from NOSbF6 and coordination complex of Ag ion and aldehyde product ([Ag·22]+SbF6–) from AgSbF6. Single crystal X‐ray analyses reveal the different structure generated by different salt. UV/Vis absorption spectra and calculation demonstrate the formation of both compounds. It provides an example of chemoselectivity of Wagner–Meerwein 1,2‐shifts in pinacol rearrangement that depends upon different oxidant. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An unexpected ketone formation in the synthesis of tetrabenzo[a,d,j,m]coronene. • Pinacol-pinacolone type rearrangement. • Single-crystal diffraction study for the characterization. Abstract An unexpected ketone was obtained in the synthesis of tetrabenzo[a,d,j,m]coronene having tert-butyl groups from Thiele's hydrocarbon derivative. The structure of the product was confirmed by not only spectroscopic but also diffraction studies. This product was formed by the rearrangement reaction of one phenyl group and this reaction could be analogous to the pinacol-pinacolone rearrangement. [ABSTRACT FROM AUTHOR]

Abstract A BINOL-phosphoric acid-catalyzed furylogous Pinacol rearrangement is developed. This reaction produces spiro cyclopentanone in good yields under mild conditions. The enantioselective version of this reaction is also investigated using chiral phosphoric acid (CPA) as the catalyst. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Cyclopentenyl carbocations formed as a result of the protonation of 3,4-substituted cyclopent-3-en-1,2-diols can give either cyclopent-2-en-1-one derivatives via pinacol rearrangement or interrupted reaction products similar to the Nazarov intermediate. [ABSTRACT FROM AUTHOR]

In the course of the preparation of a series of ferrocenyl derivatives of diethylstilbestrol (DES), in which one of the 4-hydroxyphenyl moieties was replaced by a ferrocenyl group, the McMurry reaction of chloropropionylferrocene with a number of mono-aryl ketones unexpectedly yielded the hydroxylated ferrocenyl DES derivatives, 5a–c, in poor yields (10%–16%). These compounds showed high activity on the hormone-independent breast cancer cell line MDA-MB-231 with IC50 values ranging from 0.14 to 0.36 µM. Surprisingly, non-hydroxylated ferrocenyl DES, 4, showed only an IC50 value of 1.14 µM, illustrating the importance of the hydroxyethyl function in this promising new series. For comparison, McMurry reactions of the shorter chain analogue chloroacetylferrocene were carried out to see the difference in behaviour with mono-aryl ketones versus a diaryl ketone. The effect of changing the length of the alkyl chain adjacent to the phenolic substituent of the hydroxylated ferrocenyl DES was studied, a mechanistic rationale to account for the unexpected products is proposed, and the antiproliferative activities of all of these compounds on MDA-MB-231 cells lines were measured and compared. X-ray crystal structures of cross-coupled products and of pinacol-pinacolone rearrangements are reported.

A catalytic pinacol-type reductive rearrangement reaction of internal 1,2-diols is reported herein. Several scaffolds not usually amenable to pinacol-type reactions, such as aliphatic secondary-secondary diols, undergo the transformation well without the need for prefunctionalization. The reaction uses a simple boron catalyst and two silanes and proceeds through a concerted, stereoinvertive mechanism that enables the preparation of highly enantiomerically enriched products. Computational studies have been used to rationalize the preference for migration over direct deoxygenation. [ABSTRACT FROM AUTHOR]

The direct transesterification of dioxaborolanes (alkane-1,2-diol based boronate esters) was explored. Using BF 3 ·OEt 2 , alkane-1,2-diol based mono- and bis-boronate esters (i.e., pinacol and ethylene glycol) have been converted quantitatively to either benzene-1,2-diol or alkane-1,3-diol based boronate esters. In the case of pinacol esters, esterification is facilitated by the accompanying pinacol rearrangement, thus shifting the reaction equilibrium. [ABSTRACT FROM AUTHOR]

The first catalytic enantioselective asymmetric aza-pinacol rearrangement is reported. The reactions are catalyzed by a chiral phosphoric acid and proceed via a highly organized transition state involving a cyclic aza- ortho-xylylene intermediate to afford the indoline structures with good to excellent enantioselectivity. The synthetic utility of this method is demonstrated by the asymmetric synthesis of a key intermediate to the natural product minfiensine and the identification of a chiral lead compound to repress antibiotic resistance. [ABSTRACT FROM AUTHOR]

1,2-Carbon atom rearrangement has been broadly applied as a guiding strategy in complex molecule assembly. As it entails the carbon–carbon or carbon–heteroatom bond migration between two vicinal atoms, this type of reaction is capable of generating structural complexity through a molecular skeletal reorganization. This review will focus on recent employment of this strategy in the total synthesis of natural products, highlighting the exceptional utility of such synthetic methodologies in the construction of intricate carbocycles, heterocycles or structurally complex motifs from synthetically more accessible precursors. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) and carboxylic acid functionalized GO (GO-CO2H) have been found to efficiently promote the heterogeneous and environmentally friendly pinacol rearrangement of 1,2-diols and the direct nucleophilic substitution of allylic alcohols. In general, high yields and regioselectivities are obtained in both reactions using 20 wt % of catalyst loading and mild reaction conditions. [ABSTRACT FROM AUTHOR]

A 'Prins pinacol type rearrangement followed by C4-OBn participation' in a cascade manner has been observed while probing the fate of carbocation in some carbohydrate derived homoallylic alcohols in the Prins reaction. This has led to an easy access to tetrahydrofuran-fused bridged bicyclic ketals (or tetrahydrofuran-fused 1,6-anhydro-heptopyranose frameworks) which are further converted into some annulated sugars and C2-branched heptoses. [ABSTRACT FROM AUTHOR]

An enantioselective pinacol rearrangement of functionalized ( E)-2-butene-1,4-diols was developed. In the presence of a catalytic amount of a chiral BINOL-derived N-triflyl phosphoramide, these 1,4-diols rearranged to β,γ-unsaturated ketones in excellent yields and enantioselectivities. The formation of a chiral ion pair between the intermediary allylic cation and the chiral phosphoramide anion was postulated to be responsible for the highly efficient chirality transfer. These chiral building blocks were further converted into enantioenriched polysubstituted tetrahydrofuran and tetrahydronaphthalene derivatives. [ABSTRACT FROM AUTHOR]

Promising results of an efficient and convenient strategy for the annulation of polycyclic aromatic compounds (PACs), employing orthoquinones as starting material and comprising allylation, pinacol rearrangement, ring-closing metathesis (RCM), and one-pot reduction followed by Wagner-Meerwein rearrangement, are presented. The strategy involves introducing triallylborane prepared in situ in the allylation step. Moreover, a novel expedient method for the preparation of 9,10-diallylphenanthrene was introduced.

Natural sunlight offers a cost-efficient and sustainable energy source for photochemical reactions. In contrast to the lengthy and small-scale “flask in the sun” procedures of the past, modern solar concentrator systems nowadays significantly shorten reaction times and enable technical-scale operations. After a brief historical introduction, this review presents the most important solar reactor types and their successful application in preparative solar syntheses. The examples demonstrate that solar manufacturing of fine chemicals is technically feasible and environmentally sustainable. After over 100 years, Ciamician's prophetic vision of “the photochemistry of the future” as a clean and green manufacturing methodology has yet to be realized. At the same time, his warning “for nature is not in a hurry but mankind is” is still valid today. It is hoped that this review will lead to a renewed interest in this truly enlightening technology, that it will stimulate photochemists and photochemical engineers to “go back to the roots onto the roofs” and that it will ultimately result in industrial applications in the foreseeable future. [ABSTRACT FROM AUTHOR]

3-Chloroquinoline-2,4-diones were reduced with sodium borohydride to give syn - and anti -chlorohydrins, the stereochemistry of which was established by NMR spectroscopy. Both stereoisomeric chlorohydrins were reacted with potassium carbonate in methanol. anti -Isomers afforded the corresponding epoxides or rearranged to 3-hydroxy-4-alkylquinolin-2-ones, whereas syn -isomers did not react. However, these isomers converted to 4-hydroxyquinolin-2-ones after standing for a long period of time in DMSO. After reaction with thionyl chloride, the syn -isomers yielded cis - and trans -3,4-dichloroquinolin-2-ones. [ABSTRACT FROM AUTHOR]

Although the widespread usage of aza-pinacol and aza-semipinacol rearrangements as synthetic methods has not been found, these synthetic transformations offer novel tactics for the preparation of nitrogen-containing heterocycles and natural alkaloids. Herein, we briefly discuss the most recent developments in this area and present our strategy based on aza-pinacol rearrangements for the synthesis of indolines and indolenines. [ABSTRACT FROM AUTHOR]

By alkylation of 4,4-disubstituted 2-(ethoxycarbonyl)butanolides new 4,4-disubstituted 2-alkenyl-2-(ethoxycarbonyl)butanolides were synthesized, which at alkaline hydrolysis formed 4,4-disubstituted 2-alkenylbutanolides. By oxidation of the latter with hydrogen peroxide and formic acid diololactones were obtained that in conditions of pinacol-pinacolone rearrangement and oxidation with lead tetraacetate afforded formyl- and epoxybutanolides of new structure. [ABSTRACT FROM AUTHOR]