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.     

Catalytic Silylations of Alcohols: Turning Simple Protecting‐Group Strategies into Powerful Enantioselective Synthetic Methods

In recent years, remarkable progress has been made in the enantioselective silylation of alcohols. Owing to the successful site‐ and stereoselective functionalization of hydroxy groups, silyl ether formations have evolved from being a simple reaction for functional‐group protection into a powerful enantioselective process. In this Minireview, we highlight important recent findings in this emerging field.     

Enantioselective 1,3-dipolar cycloaddition of nitrones catalyzed by optically active cationic cobalt(III) complexes

[reaction: see text] The optically active beta-ketoiminato cationic cobalt(III) complexes were employed as efficient Lewis acid catalysts for the enantioselective 1,3-dipolar cycloaddition reaction of alpha,beta-unsaturated aldehydes with nitrones. Excellent endo selectivities and high enantioselectivities were achieved in the cycloaddition reaction of 1-cyclopentene-1-carbaldehyde and the nitrones derived from 2-halobenzaldehyde.     

Kinetic Resolution of 2H‐Azirines by Asymmetric Imine Amidation

Highly efficient kinetic resolution of 2H‐azirines by an asymmetric imine amidation was achieved in the presence of a chiral N,N′‐dioxide/Sc^III complex, thus providing a promising method to obtain the enantioenriched 2H‐azirine derivatives and protecting‐group free aziridines at the same time. It is rare to find an example of N1 of an oxindole participating in a reaction over C3. Moreover, chiral 2H‐azirines were stereospecifically transformed into an unprotected aziridine and α‐amino ketone.     

Stereoarrayed CF3‐Substituted 1,3‐Diols by Dynamic Kinetic Resolution: Ruthenium(II)‐Catalyzed Asymmetric Transfer Hydrogenation

CF₃‐substituted 1,3‐diols were stereoselectively prepared in excellent enantiopurity and high yield from CF₃‐substituted diketones by using an ansa‐ruthenium(II)‐catalyzed asymmetric transfer hydrogenation in formic acid/triethylamine. The intermediate mono‐reduced alcohol was also obtained in very high enantiopurity by applying milder reaction conditions. In particular, CF₃C(O)‐substituted benzofused cyclic ketones underwent either a single or a double dynamic kinetic resolution during their reduction.     

光学活性氰醇的合成研究进展

光学活性氰醇是合成大量医药、农药产品的重要中间体。本文介绍了通过生物或化学催化剂进行外消旋底物的拆分或前手性底物的不对称化来制备光学活性氰醇的方法,重点讨论了有较大发展前景的有机溶剂中脂肪酶催化氰醇酯的动力学拆分的方法。     

Kinetic Resolution of Azomethine Imines by Brønsted Acid Catalyzed Enantioselective Reduction

Azomethine imines are valuable substrates in asymmetric catalysis, and can be precursors to β‐amino carbonyl compounds and complex hydrazines. However, their utility is limited because complex and enantioenriched azomethine imines are often unavailable. Reported herein is a kinetic resolution of N,N′‐cyclic azomethine imines by enantioselective reduction (s=13–43). This resolution was accomplished using a Brønsted acid catalyst, and represents the first example of the asymmetric reduction of azomethine imines. The pyrazolidinone product (up to 86 % ee) and the recovered azomethine imine (up to 99 % ee) can both be used to access the opposite enantiomers of valuable products.     

Diastereo‐ and Enantioselective anti‐Selective Hydrogenation of α‐Amino‐β‐keto Ester Hydrochlorides and Related Compounds Using Transition‐Metal–Chiral‐Bisphosphine Catalysts

This review describes our recent works on the diastereo‐ and enantioselective synthesis of anti‐β‐hydroxy‐α‐amino acid esters using transition‐metal–chiral‐bisphosphine catalysts. A variety of transition metals, namely ruthenium (Ru), rhodium (Rh),iridium (Ir), and nickel (Ni), in combination with chiral bisphosphines, worked well as catalysts for the direct anti‐selective asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides, yielding anti‐β‐hydroxy‐α‐amino acid esters via dynamic kinetic resolution (DKR) in excellent yields and diastereo‐ and enantioselectivities. The Ru‐catalyzed asymmetric hydrogenation of α‐amino‐β‐ketoesters via DKR is the first example of generating anti‐β‐hydroxy‐α‐amino acids. Complexes of iridium and axially chiral bisphosphines catalyze an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides via dynamic kinetic resolution. A homogeneous Ni–chiral‐bisphosphine complex also catalyzes an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides in an anti‐selective manner. As a related process, the asymmetric hydrogenation of the configurationally stable substituted α‐aminoketones using a Ni catalyst via DKR is also described.     

Enantioselective diene Cyclization/Hydrosilylation catalyzed by optically active palladium bisoxazoline and pyridine-oxazoline complexes

A 1:1 mixture of (N-N)Pd(Me)Cl ?N-N = (S,S)-4,4'-dibenzyl-4,5,4', 5'-tetrahydro-2,2'-bisoxazoline (S,S-4a) and NaBAr(4) ?Ar = 3, 5-C(6)H(3)(CF(3))(2) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of dimethyl diallylmalonate (2) and triethylsilane at -30 degrees C for 48 h to form an 8.1:1 mixture of the silylated carbocycle (S,S)-trans-1, 1-dicarbomethoxy-4-methyl-3-?(triethylsilyl)methylcyclop ent ane (S, S-3) (95% de, 72% ee) and dimethyl 3,4-dimethylcyclopentane-1, 1-dicarboxylate (S,S-6) in 64% combined yield. In comparison, a 1:1 mixture of the palladium pyridine-oxazoline complex (N-N)Pd(Me)Cl ?N-N = (R)-(+)-4-isopropyl-2-(2-pyridinyl)-2-oxazoline (R-5b) and NaBAr(4) (5 mol %) catalyzed the asymmetric cyclization/hydrosilylation of 2 and triethylsilane at -32 degrees C for 24 h to form carbocycle S,S-3 in 82% yield (>95% de, 87% ee) as the exclusive product. Asymmetric diene cyclization catalyzed by complex R-5b was compatible with a range of functional groups and produced carbocycles with up to 91% ee. The procedure also tolerated substitution at a terminal olefinic position and at the allylic position of the diene.