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.

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.