Highly chemo-, diastereo-, and enantioselective reduction of 1,2-dialkyl-3-aryl-1,3-diketones for preparation of aldol-type compounds

[reaction: see text]. Highly chemo-, diastereo-, and enantioselective borohydride reduction of 2-substituted-1,3-diketones was achieved in the presence of the optically active beta-ketoiminato cobalt complex catalysts to afford the optically active 2-substituted-3-hydroxyketones. The present catalytic and enantioselective reduction could provide an alternative potential for preparation of optically active anti-aldol-type compounds.     

Enantioselective borodeuteride reduction of aldimines catalyzed by cobalt complexes: preparation of optically active deuterated primary amines

[reaction: see text] The enantioselective borodeuteride reduction catalyzed by optically active beta-ketoiminato cobalt complexes was applied to N-(di(o-tolyl)phosphinyl)aldimines to afford the corresponding optically active deuterated primary amines in high yields with high enantiomeric excesses after simple deprotection. The present deuteride reduction of aldimines is in the opposite sense of the enantioselective for the previously reported borohydride reduction of ketones or diphenylphosphinyl aldimines. The stereochemical course in these enantioselective reductions is discussed.     

Enantioselective, biocatalytic reduction of 3-substituted cyclopentenones: application to the asymmetric synthesis of an hNK-1 receptor antagonist

A convergent and enantioselective route to the hNK-1 receptor antagonist (1) is described, which sets all six stereogenic centers with high diastereoselectivity and delivers 1 in only 11 steps and 23% overall yield. The process was enabled by the development of the enantioselective enzymatic reduction of 3-functionalized cyclopentenones and stereospecific Pd-catalyzed etherification coupling of fragments 6 and 7.     

Enantioselective borohydride reduction catalyzed by optically active cobalt complexes

The highly enantioselective borohydride reduction of aromatic ketones or imines to the corresponding alcohols was developed in the presence of a catalytic amount of an optically active cobalt(II) complex catalyst. This enantioselective reduction is carried out using a precisely premodified borohydride with alcohols such as tetrahydrofurfuryl alcohol, ethanol and methanol. High optical yields are obtained by choosing the appropriate alcohol as modifiers and a suitable beta-ketoiminato ligand of the catalyst. The enantioselective borohydride reduction has been successfully applied to the preparation of optically active 1,3-diols, the stereoselective reduction of diacylferrocenes, and dynamic and/or kinetic resolution of 1,3-dicarbonyl compounds.     

Highly enantioselective borohydride reductions of 2-phenacylpyridine catalyzed by optically active β-ketoiminato cobalt(II) complexes

The highly enantioselective reduction of 2-phenacylpyridine catalyzed by optically active β-ketoiminato cobalt(II) complexes with pre-modified sodium borohydride was achieved affording in high enantiomeric excess 1-phenyl-2-(2-pyridyl)ethanol, a precursor of sedamine derivatives. The enantioselective sense in the present reduction is discussed and compared to the asymmetric reduction catalyzed by other complex catalysts.     

Direct organocatalytic asymmetric alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds

The application of cinchona alkaloid derivatives as catalysts for enantioselective alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds by different electrophilic sulfur reagents is presented. Optically active products are obtained in good to excellent yields and up to 91 % ee. Furthermore, the diastereoselective reduction of alpha-sulfenylated beta-keto esters to give optically active alpha-sulfenylated beta-hydroxy esters has been studied. A model for the intermediate is presented, in which the protonated cinchona alkaloid interacts with the substrate leading to face-shielding in accordance with the enantioselective alpha-sulfenylation step.     

β-氨基酮不对称还原反应的理论研究

本文用AM1半经验分子轨道方法,首次从热力学和动力学角度研究了(R)-4-苄基-5,5-二苯基-1,3,2口恶唑硼烷催化还原系列β-氨基酮的反应,获得了CBS 反应机理各步的反应热及第二、第四步骤的反应活化能,结果表明第二步(催化配合物的形成)和第四步(产物的形成和催化剂的释放)为吸热反应,且第四步反应吸热较多,且活化能远高于第二步,同时发现CBS反应机理中第二步为控制反应产物构型取向的决定步骤,根据第二步反应中生成R和S型催化配合物的活化能之差可推测β-氨基酮分子中羰基对位推电子基的存在有利于获得高光学活性的氨基醇产物。     

New and efficient catalysts for enantioselective borohydride reduction of ketones and imines

Optically active aldiminato cobalt(II) complexes have been found to catalyze the enantioselective reduction of ketones with sodium borohydride affording the corresponding optically active secondary alcohols in high chemical yields with high enantioselectivities. The enantioselective borohydride reduction is also applicable to not only C=O bonds in aromatic ketones but also to C=N bonds in aromatic imines.     

The first synthesis of (-)-asperpentyn and efficient syntheses of (+)-harveynone, (+)-epiepoformin and (-)-theobroxide

A generally applicable strategy for the synthesis of a range of polyoxygenated cyclohexane natural products has been developed. The enantioselective syntheses of (-)-theobroxide, a polyoxygenated cyclohexane natural compound with potent growth inducing properties in potato microtubers has been achieved via a 1,2 O-silyl migration between trans-hydroxyl groups and a remote hydroxyl directed epoxidation of an enone derived from quinic acid. A thus derived alpha-iodoenone was subjected to Stille coupling with tetramethylstannane to afford the first title compound. A similar strategy enabled a route to the complete asymmetric synthesis of the acetylenic phytotoxin (+)-harveynone. By selective reduction of (-)-theobroxide, (+)-epiepoformin was also prepared in enantiopure form and similarly, stereoselective reduction of (+)-harveynone completed the first enantioselective synthesis of (-)-asperpentyn, another natural compound with antimicrobial activity.     

Enantioselective Biocatalytic Reduction of Hexan-2-one,Catalyzed by Petroselinum crispum Cells

Russian Journal of General Chemistry - A method for the synthesis of (2S)-(+)-hexan-2-ol, a precursor of a number of drugs, by the enantioselective biocatalytic reduction of a prochiral...     

吡咯烷并手性噁唑硼烷催化芳香酮的不对称还原机理的量子化学研究

不对称催化还原;吡咯烷并手性噁唑硼烷催化芳香酮的不对称还原机理的量子化学研究     

Enantioselective reduction of acetophenone analogues using carrot and celeriac enzymes system

<正>The enantioselective reduction of acetophenone analogues catalyzed by carrot and celeriac was performed in moderate conversions and excellent enantiomeric excesses.The steric factors and electronic effects of the substituents at the aromatic ring were found to significantly affect the efficiency of the enantioselective reduction of acetophenone analogues,while they had a little effect on the enantioselectivity of acetophenone analogues reduction.It was also found that the conversions of acetophenone analogues reduction at 33℃by means of both biocatalysts were three times as great as those at room temperature.     

Highly enantioselective total synthesis of (+)-isonitramine

A new efficient enantioselective synthetic method of (+)-isonitramine is reported. (+)-Isonitramine was obtained in 12 steps (98% ee and 43% overall yield) from δ-valerolactam via enantioselective phase-transfer catalytic alkylation, Dieckman condensation, and diastereoselective reduction as key steps.     

Synthetic studies toward mannopeptimycin-E: synthesis of the O-linked tyrosine 1,4-alpha,alpha-manno,manno-pyranosyl pyranoside

[structure: see text] The enantioselective synthesis of the C-4' acylated 1,4-alpha,alpha-manno,manno-disaccharide fragment of mannopeptimycin-E has been achieved in seven steps from d-tyrosine. The route relies upon diastereoselective palladium-catalyzed glycosylation, diastereoselective reduction, and diastereoselective bis-dihydroxylation. The efficiency of the synthesis is demonstrated by the high overall yield (37%) and the preparation of various analogues.     

Enantioselective syntheses of cryptocarya triacetate,cryptocaryolone, and cryptocaryolone diacetate

[reaction: see text] The enantioselective syntheses of three natural products from Cryptocarya latifolia have been achieved in 13-15 steps from ethyl sorbate. The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to establish the absolute stereochemistry. The route also relies upon a highly (E)-selective olefin cross-metathesis reaction to form trans-delta-hydroxy-1-enoates. The resulting delta-hydroxy-1-enoates were subsequently converted into cryptocarya triacetate, cryptocaryolone, and cryptocaryolone diacetate.     

A concise total synthesis of lyngbic acid,hermitamides A and B

A concise total syntheses of lyngbic acid, hermitamides A and B have been accomplished in a highly enantioselective manner involving CBS asymmetric reduction, hydroboration, and stereospecific Julia–Lythgoe olefination.     

Quantum chemical modeling of chiral catalysis. Part 8. On the conformational freedom of the ketone of ketone-borane complexes of oxazaborolidines used as catalysts in the enantioselective reduction of ketones

Standard ab initio molecular orbital methods were employed to study conformational freedom of the ketone of ketone-borane complexes of chiral oxazaborolidines used as catalysts for the enantioselective reduction of ketones (CBS reduction). A formaldehyde-borane complex of 1,3,2-oxazaborolidine was used as a model system. A new conformation was found which was energetically more advantageous than the original one predicted by Corey et al. The new conformation was predicted to be destabilized by bulky substituents at the C-5 of the ring. A new class of potential oxazaborolidine catalysts for the enantioselective reduction of ketones was invented.     

Preparation of chiral secondary boronic esters via copper-catalyzed enantioselective conjugate reduction of β-boronyl-β-alkyl α,β-unsaturated esters

A new methodology involving the copper(I)-catalyzed enantioselective conjugate reduction of β-boronyl-β-alkyl enoates was developed. Various chiral secondary boronate derivatives can be accessed in excellent yields and good to high levels of enantioselectivity through this efficient copper-catalyzed process using polymethylhydrosiloxane (PMHS) as hydride source.     

An enantioselective enzymatic desymmetrization route to hexahydro-4H-furopyranol,a high-affinity ligand for HIV-1 protease inhibitors

An enantioselective synthesis of (3aS,4S,7aR)-hexahydro-4H-furo[2,3-b]pyran-4-ol, a high-affinity nonpeptide ligand for a variety of potent HIV-1 protease inhibitors is described. The key steps involved a highly enantioselective enzymatic desymmetrization of meso-diacetate, an efficient transacetalization, and a highly diastereoselective reduction of a ketone. This route is amenable to large-scale synthesis using readily available starting materials.     

A short and efficient enantioselective route to a key intermediate for the total synthesis of forskolin

A simple route for the enantioselective synthesis of key intermediates (11 and 12) for the total synthesis of forskolin has been developed starting from acid 6 and (S)-alcohol 5. The latter is prepared by enantioselective catalytic CBS reduction of dienone 3, and is converted by an intramolecular Diels-Alder reaction to tricyclic lactone 9.