Enantioselective Alkylations of Tributyltin Enolates Catalyzed by Cr(salen)CI:Access to Enantiomerically Enriched All-Carbon Quaternary Centers

摘要

alpha-Alkylations of carbonyl compounds are indispensable C-C bond-forming reactions in synthetic organic chemistry.Asymmetric variants rely predominantly upon the use of chiral auxiliaries,which often provide exceptional levels of selectivity.For both practical and fundamental reasons,broadly applicable catalytic asymmetric alkylation reactions of enolates have been a long-sought goal.Whereas highly efficient transition-metal-catalyzed asymmetric a-allylations,arylations,and vinylations of ketones have been identified,relatively limited progress has been made in catalytic alkylations with sp3-hybridized electrophiles.Three distinct strategies for catalytic alkylation with alkyl halides have been reported,each involving organic molecules as catalysts.