Nickel/N-Heterocyclic Carbene Complex-Catalyzed Enantioselective Redox-Neutral Coupling of Benzyl Alcohols and Alkynes to Allylic Alcohols

The
nickel-catalyzed enantioselective redox-neutral coupling of
alcohols and alkynes to access chiral allylic alcohols is reported.
The reaction proceeds via a hydrogen transfer process under ambient
temperature, converting abundant feedstock alcohols and alkynes to
chiral allylic alcohols with high stereoselectivities in one chemical
step. Key to the success of this process was the development of a
bulky chiral N-heterocyclic carbene, (R,R,R,R)-SIPE, a chiral version of
SIPr, as the ligand for nickel. Notably, we found that the utilization
of P­(OPh)3 as secondary ligand for nickel was crucial to
inhibit the isomerization of products.