Double Asymmetric Hydrogenation of Linear b,b-Disubstituted α,β-Unsaturated Ketones into g-Substituted Secondary Alcohols using a Dual Catalytic System

摘要

Double asymmetric hydrogenation of linear b,bdisubstituted a,b-unsaturated ketones catalyzed by the DM-SEGPHOS/DMAPEN/RuII complex with t-C_4H_9OK afforded the g-substituted secondary alcohols in high diastereoand enantioselectivities. Some mechanistic experiments suggested that two different reactive species, type (I) and (II), were reversibly formed in this catalytic system: Type (I) with the diamine ligand DMAPEN enantioselectively hydrogenated the enones into the chiral allylic alcohols, and type (II) without the diamine ligand diastereoselectively hydrogenated the allylic alcohols into the g-substituted secondary alcohols. This dual catalysis protocol was successfully applied to the reaction of a variety of aliphaticand aromatic-substituted enone substrates.