Palladium-Catalyzed Asymmetric Allylic Alkylation of Ketone Enolates

摘要

Palladium-catalyzed asymmetric allylic alkylation of nonstabi-lized ketone enolates to generate quaternary centers has been achieved in excellent yield and enantioselectivity.Optimized conditions consist of performing the reaction in the presence of two equivalents of LDA as base,one equivalent of trimethytin chloride as a Lewis acid,1,2-dimethoxyethane as the solvent,and a catalytic amount of a chiral palladium complex formed from Jt-allyl palladium chloride dimer 3 and cyclohexyldiamine derived chiral ligand 4.Linearly substituted,acyclic 1,3-di-alkyl substituted,and unsubstituted allylic carbonates function well as elec-trophiles.A variety of a-tetralones,cy-clohexanones,and cyclopentanones can be employed as nucleophiles.The absolute configuration generated is consistent with the current model in which steric factors control stereofacial differentiation.The quaternary substituted products available by this method are versatile substrates for further elaboration.