Stereochemical editing:Catalytic racemization of secondary alcohols and amines

Chiral alcohols and amines are important structural units widely existing in pharmaceuticals,agrochemicals,and food additives.Dynamic kinetic resolution(DKR)is an efficient strategy to deliver optically active alcohols and amines from their racemates.For the development of DKR method,racemization catalyst plays as a crucial element with the requirement of compatibility with the kinetic resolution(KR)system.In this paper,recent advance in the catalytic racemization of secondary alcohols and amines is summarized based on different types of racemizing intermediates,which are redox racemization via ketone/imine intermediates,racemization via radical intermediates,and racemization via carbocation intermediates.Enzymatic racemization of secondary alcohols and amines is also enclosed.

Visible Light-Mediated Cobalt and Photoredox Dual-Catalyzed Asymmetric Reductive Coupling for Axially Chiral Secondary Alcohols

Secondary alcohols bearing both axial and central chirality comprise attractive biological activity and exhibit excellent chiral induction in asymmetric reactions.However,only very limited asymmetric catalytic approaches were developed for their synthesis.We herein describe visible light-mediated cobalt-catalyzed asymmetric reductive Grignard-type addition of aryl iodides with axially prochiral biaryl dialdehydes leading to the direct construction of axially chiral secondary alcohols.Preliminary mechanistic studies indicate that efficient kinetic recognition of diastereomers might occur for axially prochiral dialdehydes to improve the stereoselectivity,which might open a new avenue for the challenging cascade construction of multiple chiral elements.This protocol features excellent enantio-and diastereoselectivity,green and mild conditions,simple operation,and broad substrate scope,providing a modular platform for the synthesis of secondary axially chiral alcohols.

Salen-Mn(III)-Complex-Catalyzed Oxidations of Secondary Alcohols

Secondary alcohols were catalytically oxidized with diacetoxyiodobenzene as oxidant in the presence of salen- Mn(III) complex to afford the corresponding ketones, in up to 99% yield, using CH 2Cl 2 or water as reaction media.

Base-controlled NHC-Ru-catalyzed transfer hydrogenation andα-methylation/transfer hydrogenation of ketones using methanol

Herein,we report the NHC-Ru catalyst system that realizes the chemo-selective transformation of ketones with methanol.By simply changing the base,a broad range of structurally diverse ketones,could be selectively and efficiently converted to the correspondingβ-methylated secondary alcohols or secondary alcohols.Remarkably,this catalytic system was very effective for the synthesis of bio-related molecules and deuterated alcohols,as well as the three-component coupling between methyl ketones,primary alcohols,and methanol.The reaction mechanism was further revealed by experiment and DFT mechanistic investigations.

Chemo-and Enantioselective Arylation and Alkenylation of Aldehydes Enabled by Nickel/N-Heterocyclic Carbene Catalysis

Herein,we report the first highly enantioselective Ni-catalyzed arylation and alkenylation of simple aldehydes using readily available and stable organoboronic esters.This protocol provides various chiral secondary alcohols in high yields and enantioselectivities(up to 97% ee)with a broad scope of substrates,functional groups,and heterocycles.The use of a bulky N-heterocyclic carbene(NHC)ligand for nickel catalyst is the key to high enantiocontrol.The competitive Ni-catalyzed transformations,including Tishchenko reaction,dehydrogenation/hydrogenation reaction,and Suzuki-Miyaura couplings,are avoided.The excellent chemoselectivity is likely due to the application of mild base CsF and η^(2)-coordination of aldehydes with nickel.