Search

Choosing the optimal catalyst for a new transformation is challenging because the ideal molecular requirements of the catalyst for one reaction do not always simply translate to another. Large groups at the 3,3′ positions of the binaphthol rings are important for efficient stereoinduction but if they are too large this can lead to unusual or poor results. By applying a quantitative steric assessment of the substituents at the 3,3′ positions of the binaphthol ring, we have systematically studied the effect of modulating this group on enantioselectivity for a wide range of reactions involving imines, and verified this analysis using ONIOM calculations. We have shown that in most reactions, the stereochemical outcome depends on both proximal and remote sterics. Summarising detailed calculations into a simple qualitative model identifies and explains the steric features required for high selectivity. This model is consistent with seventy seven papers reporting reactions (over 1000 transformations in total), and provides a straightforward decision tree for selecting the best catalyst. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of both polysubstituted oxazolo-pyrrolidinones and -piperidinones by a domino process. The methodology is based on the reaction between hydroxyl halogenoamides and Michael acceptors, which leads efficiently to bicyclic lactams. The process is compatible with unsymmetrical electron-withdrawing groups on the Michael acceptor, which allows the formation of two contiguous and fully controlled tertiary and quaternary stereocenters. In the case of tetrasubstituted Michael acceptors, two adjacent quaternary stereocenters are formed in good yield. Starting from ( R)-phenylglycinol derived amides results in the formation of enantioenriched bicyclic lactams in low to good yields and with high levels of stereoselectivity, thus greatly increasing the scope and interest of this strategy. The origins of chirality transfer and diastereoselectivity were studied by DFT calculations and have been attributed to a kinetic control in one of the last two steps of the reaction sequence. This selectivity is dependent upon both the substituents on the Michael acceptor and the sodium cation chelation. [ABSTRACT FROM AUTHOR]

From the reaction of manganese halides with the chiral Schiff bases obtained by condensation of o‐vanillin and (R)‐ or (S)‐phenylglycinol, 11 complexes based on pentanuclear cages with trigonal bipyramidal [MnIIMnIII3M′] (M′=NaI, CaII, MnII) or enneanuclear [MnIIMnIII6NaI2] cores were synthesized. Structural, supramolecular chirality, and optical properties were explored. The magnetic properties of related systems were reviewed, and the magnetic response of the new systems was rationalized to the bond parameters. Mirror, mirror: A family of chiral clusters with [MnIIMnIII3M′] or [MnIIMnIII6NaI2] cores (see figure) was obtained from enantiomerically pure Schiff bases. Structural characteristics, optical properties, and magnetic response were studied for these complexes. [ABSTRACT FROM AUTHOR]

Accurate identifying and in‐depth understanding of the defect sites in a working nanomaterial could hinge on establishing specific defect‐activity relationships. Yet, atomically precise coinage‐metal nanoclusters (NCs) possessing surface vacancy defects are scarce primarily owing to challenges in the synthesis and isolation of such defective NCs. Herein we report a mixed‐ligand strategy to synthesizing an intrinsically chiral and metal‐deficient copper hydride‐rich NC [Cu57H20(PET)36(TPP)4]+ (Cu57H20). Its total structure (including hydrides) and electronic structure are well established by combined experimental and computational results. Crystal structure reveals Cu57H20 features a cube‐like Cu8 kernel embedded in a corner‐missing metal‐ligand shell of Cu49(PET)36(TPP)4. Single Cu vacancy defect site occurs at one corner of the shell, evocative of mono‐lacunary polyoxometalates. Theoretical calculations demonstrate that the above‐mentioned point vacancy causes one surface hydride exposed as an interfacial capping μ3‐H−, which is accessible in chemical reaction, as proved by deuterated experiment. Moreover, Cu57H20 shows catalytic activity in the hydrogenation of nitroarene. The success of this work opens the way for the research on well‐defined chiral metal‐deficient Cu and other metal NCs, including exploring their application in asymmetrical catalysis. [ABSTRACT FROM AUTHOR]

The first stereoselective version of an iodine(III)-mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α-arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid-based iodine(III) reagents product selectivities of up to 73 % ee have been achieved. [ABSTRACT FROM AUTHOR]

The pores/channels of porous 3D metal-organic frameworks (MOFs) have been widely applied to incorporate gas, solvent, or organic molecules. On the contrary, the utilization of the interlamellar void of layered metal-organic complexes (MOCs) remains underappreciated, although it is more flexible and available to accommodate molecules with different sizes. In this work, diverse sulfonates have been intercalated purposely into an identical layered MOC, which constructed various novel intercalation compounds possessing fluorescent, white-light emitting, photochromic, homochiral, or nonlinear optical (NLO) properties. With the help of single-crystal X-ray diffraction, their structures and the mutual interactions between the MOC host and the sulfonate guests were characterized. The properties of the guest molecules were tuned and meanwhile some new performances were generated after confining them into the interlayer region. Such a hybrid approach provides an efficient strategy to design and prepare multifunctional materials. [ABSTRACT FROM AUTHOR]

Organocopper reagents react with readily available chiral conjugated diene-ynes to give indene derivatives bearing two stereogenic centres. The investigation of this original reaction in optically pure series demonstrates that a double transfer of chirality is operating. A stereocontrolled cascade involving SN2' followed by carbocupration and conjugate addition reactions accounts for the total recovery of the initial chirality. The scope and limitations of the reaction were investigated. The high diastereofacial discrimination in the cyclisation step allowed the construction of the quaternary stereocentre with excellent dr and ee, with the opposite configuration depending on the E- or Z-configuration of the alkene in the starting material. Post-functionalisation of indenes allowed the synthesis of indanyl derivatives containing four contiguous stereocentres. [ABSTRACT FROM AUTHOR]

The reaction of the enantiopure, planar‐chiral α‐ferrocenyl carbocation (Sp)‐2‐(P(=S)Ph2)FcCH2+ (Fc = Fe(η5‐C5H5)(η5‐C5H3)) towards electron‐rich arenes C6H5E (E = NH2, NMe2, NiPr2, NPh2, PPh2, P(=S)Ph2, OH, SH, SMe) regarding either a nucleophilic attack of the group E or an electrophilic aromatic substitution reaction of the arene at the CH2+ unit is reported. It was found that the amino, oxo or thio functionalities gave the respective ferrocenes in various product distributions, while the P‐based species didn't. Appropriate thiophosphine derivatives could be reduced to their PIII species that were applied as supporting ligands in atropselective C,C cross‐coupling reactions for the synthesis of sterically hindered biaryls, where sandwich compound (Sp)‐1‐(PPh2)‐2‐(o‐NMe2‐C6H4)CH2‐Fc gave an ee of 69 % (1 mol‐% [Pd]), which is up to date the highest observed value for planar‐chiral ferrocenes. The absolute configuration of the chiral ferrocenes was confirmed by single‐crystal X‐ray diffraction analysis. For seleno phosphane 1‐(P(=Se)Ph2)‐2‐(CH2OH)‐Fc a unique Se single‐atom transfer occurred within its reaction with Sanger's reagent. The presence of two chemically different Se atoms in 1‐(P(=Se)Ph2)‐2‐(((2,4‐(NO2)2‐C6H3)Se)CH2)‐Fc was confirmed by 77Se{1H} NMR spectroscopy and single‐crystal X‐ray diffraction analysis, respectively. The conversion of enantiopure ferrocenylmethanol 1a into its α‐carbocation and subsequent reaction with electron‐rich arenes is investigated. They preferably undergo SEAr or SN reactions depending on E. Reduction into phosphines and usage as ligands in C,C cross‐coupling catalysis gave biaryls with up to 69 % ee. Electron‐poor substrates enabled a transfer of the P=X chalcogene (X = S, Se) towards the cation. [ABSTRACT FROM AUTHOR]

Chemoselective reduction of the strong P=O bond in the presence of weaker P–O (ester) and P–N (amide) bonds in phosphonic acid derivatives has constituted an unresolved problem in organophosphorus chemistry for years. This long‐standing problem is now solved for biologically relevant α‐hydroxy and α‐amino phosphonic as well as phosphinic acids esters and amides. The reduction of the P=O bond without concomitant scission of the ester and amide bonds is affected by use of BH3, a mild reducing agent, which affords the corresponding borane protected PIII phosphonite and phosphinite derivatives in one step. A mechanistic rationale is proposed for the role played by neighboring OH and NHR groups in facilitating the reduction, and for the observed chemo‐ and stereoselectivity. The reduction methodology described opens previously unavailable synthetic options in chemistry of α‐functionalized phosphonic and phosphinic acids by offering a unique possibility for direct modifications of oxidation level of the P‐center in these compounds. The chemoselective reduction of P=O bond in α‐hydroxy and α‐amino phosphonic/phosphinic acid derivatives can be achieved without concomitant scission of their ester and amide bonds using commercially available BH3 complexes. The reduction involves an intramolecular assistance by the proximal OH or NH groups enabling preferential removal of the phosphoryl oxygen. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The chirality of supramolecular polymeric materials is subtly affected by a delicate balance among various non‐covalent interactions, the details of which are inadequately understood. Now, a fine balance of intermolecular interactions, including closed‐shell metal–metal, dispersive and electrostatic interactions, is used to direct the delicate orientation of monomeric building blocks, thereby achieving the successful preparation of different nanostructures with distinct supramolecular chirality. Moreover, kinetically trapped and thermodynamically stable aggregates were monitored over time in the supramolecular polymerization of cationic PtII complexes. The dynamic self‐assembly process can be successfully controlled by modifying the counteranion and solvent composition. A chiral doping approach can also be used to induce the chirality of an achiral PtII complex at the supramolecular level. The chirality transfer process and the pathway complexity of a series of chiral pincer‐type PtII complexes are described. A chiral doping approach can be used to induce the chirality of an achiral PtII complex at the supramolecular level. [Pt]=PtII complex; counteranion X−. [ABSTRACT FROM AUTHOR]

The reduction of the previously known [(6‐Ph2P‐Ace‐5‐)Te]Cl with K‐selectride (K[sec‐Bu3BH]) provided the title compound (6‐Ph2P‐Ace‐5‐)2Te2 (1). The oxidation of 1 under aerobic conditions afforded the related (6‐Ph2P(O)‐Ace‐5‐)2Te2 (2). Alternatively, 2 was prepared by reduction of the previously known 6‐Ph2P(O)‐Ace‐5‐TeCl with K‐selectride. The reaction of 1 with [Cp(CO)2Fe]2 proceeded with cleavage of the Te–Te and Fe–Fe bonds with elimination of CO and gave rise to a racemic mixture of (6‐Ph2P‐Ace‐5‐)TeFe(CO)Cp (3), which contains pseudo‐tetrahedral Fe atoms in a chiral environment. Upon crystallization, the racemate most likely undergoes spontaneous resolution into a conglomerate of enantiopure crystals. [ABSTRACT FROM AUTHOR]

Binaphthol aldehydes with appended dipicolylamine moieties, (R)‐1, and (R)‐2, were synthesized. The reaction of (R)‐1 with an amino acid together with the ZnII ion produces a monomeric complex that discriminates the chirality of the bound amino acid by 1H NMR spectroscopy. The same reaction of (R)‐2, which is different from (R)‐1 by only one nitrogen atom, generates a dimeric complex that is highly enantiospecific for the l‐form of amino acids such as Phe and Trp. [ABSTRACT FROM AUTHOR]

Abstract: A chemo‐ and biocatalytic cascade approach was applied for the stereoselective synthesis of hydroxy ketones and the corresponding 1,3‐diols. A new class of tridentate N,N,O ligands was used with copper(II) complexes for the asymmetric β‐borylation of α,β‐unsaturated compounds. The complex containing ligand L5 emerged as the best performer, and it gave the organoborane derivatives with good ee values. The corresponding keto–alcohol compounds were then bioreduced by yeasts. The biotransformation set up with Rhodotorula rubra allowed (R)‐keto–alcohols and (S,S)‐diols to be obtained with up to 99 % ee and up to 99 % de in favor of the anti enantiomers. [ABSTRACT FROM AUTHOR]

We reported herein a practical approach to acyclic tertiary α-hydroxy carbonyl compounds in only two chemical steps from alkynes with excellent diastereoselectivity through the oxidation of stereodefined polysubstituted silyl ketone aminals. The products could be smoothly converted to synthetically useful enantiomerically enriched 1,2-diol derivatives. [ABSTRACT FROM AUTHOR]

Abstract: Axial naphthols are applied in asymmetric halogenative dearomatization reactions under simple and mild conditions in the work presented herein. The axial‐to‐central chirality conversion is efficiently accomplished, and the desired halogenated dearomatization products are obtained in high yields and enantioselectivities. By using commercially available halogenation reagents, the asymmetric fluorinative, chlorinative and brominative dearomatization reactions of axial naphthols derived from BINOLs are achieved. (BINOL=1,1′‐Bi‐2‐naphthol) [ABSTRACT FROM AUTHOR]

The concept of a synergistic double catalytic kinetic resolution (DoCKR) as described in this article was successfully applied to racemic acyclic anti-1,3-diols, a common motif in natural products. This process takes advantage of an additive Horeau amplification involving two successive enantioselective organocatalytic acylation reactions, and leads to diesters and recovered diols with high enantiopurities. It was first developed with C2-symmetrical diols and then further extended to non- C2-symmetrical anti diols to prepare useful chiral building blocks. The protocol is highly practical as it only requires 1 mol % of a commercially available organocatalyst and leads to easily separable products. This procedure was applied to the shortest reported total synthesis of (+)-cryptocaryalactone, a natural product with anti-germinative activity. [ABSTRACT FROM AUTHOR]

Herein, we report a simple one-pot route to enantiopure copper(I) complexes featuring a unique [2.2]paracyclophane-based P,N-ligand system. Phosphine and pyridine moieties can be varied allowing the modular synthesis of these rigid and stable [2.2]paracyclophane-based P,N-ligands. These P,N-ligands are a new ligand class for different transition-metal complexes, which is shown exemplarily for palladium(II). [ABSTRACT FROM AUTHOR]

A concise, divergent, asymmetric total syntheses of mulinane diterpenoids has been achieved. Specifically, a new strategy was developed featuring a key intramolecular Friedel-Crafts reaction to construct the chiral fused 5-6-6 tricyclic motif, followed by sequential Birch reduction, conjugate methylation, and homologation/ring-expansion reactions to furnish the desired 5-6-7 tricyclic skeleton bearing five contiguous stereocenters. With this efficient strategy, seven mulinane diterpenoids and two analogues were synthesized via late-stage functional modification or functionalization in 8.6-20 % overall yields and 11-15 steps. [ABSTRACT FROM AUTHOR]

Enantioenriched isoxazoles having a chiral side chain at the 4-position were efficiently synthesized by chirality transfer in a gold-catalyzed cyclization/intermolecular methylenetransfer sequence followed by a carbonyl ene reaction. The chiral information of the enantioenriched O-propargylic oximes was completely retained during the gold-catalyzed reaction. The subsequent carbonyl ene reaction between the resulting 4-methylenated isoxazoline and glyoxylates proceeded with excellent levels of chirality transfer by using BF3·OEt2 as a Lewis acid. According to the relationship of absolute configuration between the starting propargylic oxime and the obtained alcohol having an isoxazole, the carbonyl ene reaction proceeded in an endo manner. [ABSTRACT FROM AUTHOR]

The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent MIIMII, mixed-valent MIIMIII and heteronuclear MIIM′III species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O⋅⋅⋅O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen-bonded structure. [ABSTRACT FROM AUTHOR]

Spiro[4,5]decanes and polycyclic compounds bearing spiro[4,5]decane systems are important biofunctional molecules. Described are diastereoselective formal (4+1) cycloaddition reactions to afford oxindole-functionalized spiro[4,5]decanes and organocatalytic enantioselective Michael-Henry cascade reactions of the (4+1) cycloaddition products to generate spirooxindole polycyclic derivatives bearing the spiro[4,5]decane system. Spiro[4,5]decanes bearing oxindoles containing three stereogenic centers and spirooxindole polycycles having seven stereogenic centers, including two all-carbon chiral quaternary centers and one tetrasubstituted chiral carbon center, were obtained with high diastereo- and enantioselectivities. [ABSTRACT FROM AUTHOR]

We report an unprecedented organocatalytic enantioselective acyloin rearrangement of α,α-disubstituted α-hydroxy acetals. In the presence of a catalytic amount of chiral binol-derived N-triflyl phosphoramide, α-hydroxy acetals rearranged to α-alkoxy ketones in good to high yields with high enantioselectivities. Formation of an ion pair between the in situ generated oxocarbenium ion and the chiral phosphoramide anion was proposed to be responsible for the highly efficient transfer of chirality. Conditions for removal of cyclohexyl and cyclopentyl groups from the corresponding α-alkoxy ketones were uncovered underpinning their potential general utility as hydroxy protecting groups. Conversion of the rearranged products to the enantioenriched α-hydroxy ketone, 1,2-diol, β-amino alcohol and 1,4-dioxane was also documented. [ABSTRACT FROM AUTHOR]

The reactions between the chiral helicene-like ligand (L) and either Ln(hfac)3·2H2O (hfac– = 1,1,1,5,5,5-hexafluoroacetylacetonate), Ln(tta)3·2H2O (tta– = 2-tenoyltrifluoroacetonate), iron(II) sulfate or chloride, or a combination of them led to the formation of five chiral 4f compounds of formula [HL][Ln(hfac)4]·nCH2Cl2 [Ln = Dy, n = 0.5 (1) and Ln = Yb, n = 1 (2)], [HL][Ln(tta)4]·nC6H14 [Ln = Dy, n = 0 (3) and Ln = Yb, n = 2.5 (4)], and [HL]2[Yb8(hfac)12(OH)12(O)]·0.5C6H14·H2O (5), a chiral 3d complex of formula [Fe(NCS)2(L)]·CH3NO2 (6), and a chiral 3d/4f heterodimetallic compound of formula [Fe(tta)(L)]- [Dy(tta)4]·2.5CH2Cl2 (7). The influence of the nature of the ancillary ligand and the presence or absence of base during the synthesis on the homochiral or heterochiral arrangement of the ligands as well as the dimensionality and nuclearity of the complexes were studied. Ytterbium-based compounds 2, 4, and 5 display near-infrared (NIR) luminescence under irradiation at λ = 350 nm owing to the 2F5/2 → 2F7/2 YbIII transition (centered at λ = 1000 nm). Complex 2 displays a second NIR emission at λ = 1278 nm, which is attributed to singlet-oxygen phosphorescence (a1Δg → X3Σg -) at both room temperature and 77 K. Dynamic magnetic measurements show an out-of-phase signal for the magnetic susceptibility of 7, which can be depicted as a 3d/4f chiral heterodimetallic single-molecule magnet. [ABSTRACT FROM AUTHOR]

Synthetic routes to α,α-disubstituted allylamines have been examined. Racemic compounds were conveniently prepared by thermal Overman rearrangements of primary allylic alcohols with trisubstituted double bonds, but rearrangement of these substrates using the only commercially available compound known to catalyze enantioselective Overman rearrangements, the cobalt oxazoline palladacycle (R)-COP-Cl, failed. Instead, optically active secondary allylic alcohols with trisubstituted double bonds, obtained by Corey–Bakshi–Shibata reduction of the corresponding methyl ketones, were synthesized and converted into α,α-disubstituted allylamines through a thermal Overman rearrangement or an allylic-cyanate-to-isocyanate rearrangement. High chirality transfer (90–99 %) was obtained for both reaction sequences, but the yields were greatly improved when the allylic-cyanate-to-isocyanate rearrangement was used. [ABSTRACT FROM AUTHOR]

Synthetically versatile 3,3-disubstituted fluorooxindoles exhibiting vicinal chirality centers were obtained in high yields and with excellent enantio-, diastereo-, and regioselectivity through catalytic asymmetric fluoroenolate alkylation with allylic acetates. The reaction proceeds under mild conditions and can be scaled up without compromising the asymmetric induction. The unique synthetic usefulness of the products is highlighted by the incorporation of additional functionalities and the formation of 3-fluorinated oxindoles exhibiting an array of four adjacent centers of chirality. A new C−F bond functionalization path that provides unprecedented possibilities for the stereoselective generation of a chiral quaternary carbon center in the alkaloid scaffold is introduced. [ABSTRACT FROM AUTHOR]

Strecker synthesis has long been considered one of the prebiotic reactions for the synthesis of α-amino acids. However, the correlation between the origin of chirality and highly enantioenriched α-amino acids through this method remains a puzzle. In the reaction, it may be conceivable that the handedness of amino acids has been determined at the formation stage of the chiral intermediate α-aminonitrile, that is, the enantioselective addition of hydrogen cyanide to an imine. Herein, an enantiotopic crystal surface of an achiral imine acted as an origin of chirality for the enantioselective formation of α-aminonitriles by the addition of HCN. In conjunction with the amplification of the enantiomeric excess and multiplication of enantioenriched aminonitrile, a large amount of near enantiopure α-amino acids, with the l- and d-handedness corresponding to the molecular orientation of the imine, is reported. [ABSTRACT FROM AUTHOR]

The synthesis of enantiomerically pure 3-aryl substituted indanones is developed using an enantioselective sulfoxide-based Knoevenagel condensation/Nazarov cyclization procedure. After the reductive desulfonation of the methyl para-tolyl sulfoxide-containing chiral auxiliary under mild conditions, selected enantiomerically pure indanone is used for the divergent total syntheses of three resveratrol natural products (+)-isopaucifloral F, (+)-quadrangularin A, and (+)-pallidol. [ABSTRACT FROM AUTHOR]

The first rhodium-catalyzed intermolecular [3+2] cycloaddition reaction of vinyl aziridines and allenes for the synthesis of enantioenriched functionalized pyrrolidines was realized. [3+2] cycloaddition with the proximal C=C bond of N-allenamides gave 3-methylene-pyrrolidines in high regio- and diastereoselectivity, whereas, 2-methylene-pyrrolidines were obtained as the major products by the cycloadditions of vinyl aziridines with the distal C=C bond of allenes. Use of readily available starting materials, a broad substrate scope, high selectivity, mild reaction conditions, as well as versatile functionalization of the cycloadducts make this approach very practical and attractive. [ABSTRACT FROM AUTHOR]

Herein we describe the development of a catalytic enantioselective alkynylogous Mukaiyama aldol reaction. The reaction is catalyzed by a newly designed chiral disulfonimide and delivers chiral allenoates in high yields and with excellent regio-, diastereo-, and enantioselectivity. Our process tolerates a broad range of aldehydes in combination with diverse alkynyl-substituted ketene acetals. The reaction products can be readily derivatized to furnish a variety of highly substituted enantiomerically enriched building blocks. [ABSTRACT FROM AUTHOR]

The levorotatory enantiomers of gabosines D and E were synthesized through a divergent approach that could equally well be applied to the synthesis of the dextrorotatory enantiomers, which have been isolated from natural sources. The approach relies on an initial desymmetrization of p-methoxyphenol, followed by an enzymatic resolution that separately provides the two enantiomers of synthon 3. This versatile synthon can be further transformed into the diverse polyoxygenated cyclohexane target molecules. Key steps in the synthesis of (-)-gabosines D and E from (4 R,6 S)- 3 are the stereoselective hydroxymethylation at the α-carbonyl position leading to (+)- 4, and the subsequent reagent-controlled epoxidation of the carbon-carbon double bond. A branching in the sequence also allowed the synthesis of the anhydrogabosines (-)-epiepoxydon and (+)-phyllostine. [ABSTRACT FROM AUTHOR]

Reported herein is a bifunctional-organocatalystmediated enantioselective inverse-electron-demand 1,3-dipolar cycloaddition of C,N-cyclic azomethine imines with azlactones. The strategy provides concise access to enantioenriched C1-substituted tetrahydroisoquinolines featuring a pyrazolidinone scaffold. Moreover, the scalability and practical utility of this protocol was well demonstrated by employing a gram-scale reaction and some representative transformations. [ABSTRACT FROM AUTHOR]

The reaction of chiral alcohol-scorpionate compounds bpzbeH [bpzbeH = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butanol] or bpzteH [bpzteH = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1- para-tolylethanol] with [ZnR2] (R = Me, Et, CH2SiMe3) in a 1:2 molar ratio afforded the dinuclear chiral zinc alkyls [Zn(R)(κ2-NNµ-O)Zn(R)2] ( 1- 4) [κ2-NNµ-O = bpzbe, R = Me ( 1), Et ( 2), CH2SiMe3 ( 3); bpzte, R = Et ( 4)]. Subsequent alcoholysis or thioalcoholysis reaction with ArEH (1 equiv.; E = O, S; Ar = 2,6-C6H3Me2) yielded the chiral dinuclear mixed alkyl-alryl oxides/thioaryl oxides [(ZnR)2(κN:κN-µ-O)(µ-EAr)] ( 5- 12) [κN:κN-µ-O = bpzbe, E = O, R = Me ( 5), Et ( 6), CH2SiMe3 ( 7); bpzte, E = O, R = Et ( 8); bpzbe, E = S, R = Me ( 9), Et ( 10), CH2SiMe3 ( 11); bpzte, E = S, R = Et ( 12)]. The alcoholysis reaction of the previously reported monoalkyls [Zn(Me)(κ3-NNO)] or [Zn(R)(κ-NNµ-O)]2 with ArOH (1 equiv., Ar = 2,6-C6H3Me2) afforded the chiral aryl oxides [Zn(OAr)(κ2-NNµ-O)]2 ( 13- 14) [κ2-NNµ-O = bpzbe ( 13); bpzte ( 14)]. The X-ray crystal structures of 3, 5, 6, and 14 confirmed a dinuclear structure in all cases with the alkoxide of the heteroscorpionates in a µ-bridging mode between the ZnII centers. Variable-temperature NMR spectroscopic studies were carried out to study their dynamic behavior in solution. Complexes 1- 9 and 12 can act as single-component initiators for the ROP of ε-CL and l-/ rac-LA, and afforded materials with low molecular weights and narrow monomodal molecular weight distributions. MALDI-TOF mass spectra confirmed that for 5- 8 the initiation occurred through nucleophilic attack by the alkoxide group, rather than the alkyl group, on the lactide monomer. Furthermore, inspection of the kinetic parameters showed propagations with a pseudo-first-order dependence on monomer and catalyst concentrations. Microstructural analysis of poly( rac-lactide) revealed that the mixed alkyl/aryl oxide-substituted initiators exert a moderate level of heteroselectivity ( Ps = 0.66). [ABSTRACT FROM AUTHOR]

Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non- C2-symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity. [ABSTRACT FROM AUTHOR]

A new hybrid P,S ligand was exploited by combining a chiral β-amino sulfide and a simple diphenyl phosphite. The resultant ligand performs extremely well in a palladium-catalyzed asymmetric decarboxylative [4+2] cycloaddition reaction, thus generating multiple contiguous stereocenters and a chiral quaternary center. By doing so, a straightforward route to highly functionalized tetrahydroquinolines was developed with yields of up to 99 %, as well as 98 % ee and greater than 95:5 d.r. Moreover, mechanistic insights into this transformation and the possible stereocontrol are discussed. [ABSTRACT FROM AUTHOR]

Regulating both the chemo- and diastereoselectivity, divergently, of a reaction is highly attractive but extremely challenging. Presented herein is a catalyst-controlled switch in the chemo- and diastereodivergent annulation reactions of Morita-Baylis-Hillman carbonates, derived from isatins and 2-alkylidene-1 H-indene-1,3(2 H)-diones, in exclusive α-regioselectivity. α-Isocupreine efficiently catalyzed [2+1] reactions to access cyclopropane derivatives, and the diastereodivergent [3+2] annulations were accomplished by employing either a chiral phosphine or a DMAP-type molecule. All reactions exhibited excellent chemoselectivities, and good to remarkable stereoselectivities were furnished, thus leading to a collection of compounds with skeletal and stereogenic diversity. Moreover, DFT computational calculations elucidated the catalyst-based switch in mechanism. [ABSTRACT FROM AUTHOR]

We report a synthetic strategy for a chemoselective switch and a diastereo-divergent approach for the asymmetric reaction of 5 H-oxazol-4-ones and N-itaconimides catalyzed by l- tert-leucine-derived tertiary amine-urea compounds. The reaction was modulated to harness either tandem conjugate addition-protonation or [4+2] cycloaddition as major product with excellent enantio- and diastereoselectivities. Subjecting the enantio-enriched cycloaddition products to a basic silica gel reagent yields the diastereomer vis-à-vis the product directly obtained under conditions for addition-protonation, thus opening a diastereo-divergent route for creating 1,3-tertiary-hetero-quaternary stereocenters. Quantum chemical studies further provide stereochemical analysis for the [4+2] process and a plausible mechanism for this chemoselective switch is proposed. [ABSTRACT FROM AUTHOR]

Heteroleptic zinc(II) complexes synthesized using achiral dipyrrinato and chiral bis(oxazoline) ligands show bright fluorescence with quantum efficiencies of up to 0.70. The fluorescence originates from the 1π-π* photoexcited state localized exclusively on the dipyrrinato ligand. Furthermore, the luminescence is circularly polarized despite the achirality of the dipyrrinato ligand. Single-crystal X-ray structure analysis discloses that the chiral bis(oxazoline) ligand undergoes intramolecular π-π stacking with the dipyrrinato ligand, inducing axial chirality in the dipyrrinato moiety. [ABSTRACT FROM AUTHOR]

Asymmetric catalysis is essential for the synthesis of chiral compounds such as pharmaceuticals, agrochemicals, fragrances, and flavors. For rational improvement of asymmetric reactions, detailed mechanistic insights are required. The usefulness of quantum mechanical studies for understanding the stereocontrol of asymmetric reactions was first demonstrated around 40 years ago, with impressive developments since then: from single-point Hartree-Fock/STO-3G calculations on small organic molecules (1970s), to the first full reaction pathway involving a metal-complex (1980s), to the beginning of the density functional theory-area, albeit typically involving truncated models (1990s), to current state-of-the-art calculations reporting free energies of complete organometallic systems, including solvent and dispersion corrections. The combined studies show that the stereocontrol in asymmetric reactions largely is exerted by nonbonding interactions, including CH/π attraction and repulsive forces. The ability to rationalize experimental results opens up for the possibility to predict enantioselectivities or to design novel catalysts on basis of in silico results. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A highly enantio- and diastereoselective synthesis of 3-aminocyclopenta[ b]indoles has been developed through formal [3+2] cycloaddition reaction of enecarbamates and 3-indolylmethanols. This transformation is catalyzed by a chiral phosphoric acid that achieves simultaneous activation of both partners of the cycloaddition. Mechanistic data are also presented that suggest that the reaction occurs through a stepwise pathway. [ABSTRACT FROM AUTHOR]

Diastereoselective quaternization of ortho-sulfinylbenzyl-methylpropargylic carbanions has been carried out with various allylic, propargylic, and benzylic halides. The stereoselectivity is efficiently controlled by the sulfinyl group, acting as a remote chiral auxiliary. Desulfinylation of the resulting compounds with tBuLi provides access to enantiopure 1,5-enynes, 1,5-diynes, and 4-arylalkynes bearing all-carbon quaternary propargylic centers. [ABSTRACT FROM AUTHOR]

A highly efficient asymmetric dearomatization of indoles was realized through a cascade reaction between 2-isocyanoethylindole and alkylidene malonates catalyzed by a chiral N,N′-dioxide/MgII catalyst. Fused polycyclic indolines containing three stereocenters were afforded in good yields with excellent diastereo- and enantioselectivities through a Michael/Friedel-Crafts/Mannich cascade. When 2-substituted 2-isocyanoethylindoles were used, spiroindoline derivatives were obtained through a Michael/Friedel-Crafts reaction. [ABSTRACT FROM AUTHOR]

Acidic hydrogen containing 2-isocyano-4-methylphenyl diphenylacetate, C22H17NO2, (I), was synthesized by the base-promoted reaction between 5-methylbenzoxazole and diphenylacetyl chloride. Achiral (I) crystallizes in the chiral P212121 space group. The C[triple-bond]N bond length is 1.164 (2) Å and the angle between the OCO and 2-isocyano-4-methylphenyl planes is 69.10 (16)°. Molecules are linked via C=O...Hphenyl and bifurcated N[triple-bond]C...Hphenyl/N[triple-bond]C...Hmethine hydrogen bonds, forming one-dimensional arrays. [ABSTRACT FROM AUTHOR]

Enantioselective construction of axially chiral biaryls by direct CH bond functionalization reactions has been realized. Novel axially chiral biaryls were synthesized by the direct CH bond olefination of biaryl compounds, using a chiral [Cp*RhIII] catalyst, in good to excellent yields and enantioselectivities. The obtained axially chiral biaryls were found as suitable ligands for rhodium-catalyzed asymmetric conjugate additions. [ABSTRACT FROM AUTHOR]

We have developed a procedure for the stereoselective and diastereodivergent synthesis of densely functionalised cyclohexanes containing four stereocentres through an asymmetric Michael-initiated ring closure (MIRC) cascade reaction employing hydrogen-bond catalysis, which is able to prepare adducts with different absolute configurations starting from the same starting materials. The overall process involves a highly diastereo- and enantioselective Michael/Henry cascade reaction between a wide range of nitroalkenes and α-nitro-δ-oxo esters, allowing access to different diastereoisomers of the final adduct by introducing subtle changes in the general ( R, R)-configured bifunctional tertiary amine/squaramide catalyst structure. Moreover, this methodology is also amenable to a three-component one-pot procedure, leading to the formation of the same adducts with very good results directly from commercially available reagents, on a multigram scale, and employing a very low catalyst loading. Furthermore, a detailed experimental and computational study is described which shows the origin of the diastereodivergent behaviour of these structurally similar catalysts and the nature of the substrate-catalyst interaction. [ABSTRACT FROM AUTHOR]

A catalytic enantioselective nucleophilic aromatic substitution reaction which yields axially chiral biaryl derivatives in excellent yields with e.r. values of up to 97:3 has been developed. This process uses a chiral counterion to direct the addition of thiophenolate to a prochiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized to a range of atropisomeric structures without any reduction in enantioenrichment, thus offering access to unexplored chiral biaryl architectures. [ABSTRACT FROM AUTHOR]

Four racemic tetrahydroisoquinolines ( RS)-(±)- 1-4 were prepared from homoveratrylamine via amidation, Bischler-Napieralski reaction and the subsequent reduction. The enantiomerically pure tetrahydroisoquinolines ( S)- (−)-norcryptostyline I [( S)-(−)- 1], ( S)-(−)-norcryptostyline II [( S)-(−)- 2], ( R)-(+)-salsolidine [( R)-(+)- 3] and ( S)-(−)-norlaudanosine [( S)-(−)- 4] were then obtained in 45%, 40%, 41% and 38% yields, respectively, via resolution of the racemic compounds ( RS)-(±)- 1-4 with half equivalent of chiral acids. In addition, the enantiomerically enriched compounds ( R)-(+)- 1, ( R)-(+)- 2, ( S)-(−)- 3 and ( R)-(+)- 4 from the mother liquors were efficiently racemized via a one-pot redox method in almost quantitative yields. [ABSTRACT FROM AUTHOR]

Chiral secondary allylboronates are obtained in high enantioselectivities and 1,6:1,4 ratios by the copper-catalyzed 1,6-boration of electron-deficient dienes with bis(pinacolato)diboron (B2(pin)2). The reactions proceed efficiently using catalyst loadings as low as 0.0049 mol %. The allylboronates may be oxidized to the allylic alcohols, and can be used in stereoselective aldehyde allylborations. This process was applied to a concise synthesis of atorvastatin, in which the key 1,6-boration was performed using only a 0.02 mol % catalyst loading. [ABSTRACT FROM AUTHOR]

Astrochemistry is a discipline consolidated recently, although its roots extend back to the dawn of early civilization with the observation and mapping of the sky. The way to the understanding of the common natural laws on earth and in space paved by Galilei's observations by the telescope, has been extended in the last decades, by new technologies such as radioastronomy and space missions. Plenty of new chemistry was surprisingly discovered. Extreme rich information on the chemical 'composition' of the universe is being obtained, either from the other planets and satellites in the Solar System, from meteorites and comets, or from the interstellar space. In this article we will present selected topics regarding the chemical structures and reactions being discovered. Particular attention will be devoted to aspects considered as relevant for the prebiotic processes on earth, such as those involving chirality and its role played in the origin and evolution of life. [ABSTRACT FROM AUTHOR]

This review documents the evolution of chiral MOF catalysts from simple Lewis acid and Lewis base catalysts that afford limited selectivity to more recent advancements that exhibit high stereo- and regioselectivities. MOF-based catalysts provide unprecedented opportunities for interrogating structure-activity relationships at high structural precision and for controlling catalytic activity by using external stimuli. The most notable disadvantage of MOF-based catalysts has been the inherent instability of the materials. This hurdle, which effectively limits the reaction scope of MOF catalysts, is slowly being overcome by the advent of new binding moieties and secondary building units. [ABSTRACT FROM AUTHOR]