Chiral Bronsted Acid-Catalyzed Formal alpha-Vinylation of Cyclopentanones for the Enantioselective Construction of Quaternary Carbon Centers

摘要

An enantioselective formal alpha-vinylation of ketones for the construction of an all-carbon quaternary center was established using the vinylogous Wagner-Meerwein shift through the activation of the leaving group by a chiral phosphoramide as the chiral Bronsted acid catalyst. The present reaction afforded enantioenriched all-carbon quaternary alpha-vinyl ketones in high yields with high enantioselectivities in most cases. Experimental elucidation of the reaction mechanism suggested that the discrimination of the two prochiral faces of the positively charged allylic species and of the enantiotopic migrating groups was efficiently achieved by the chiral phosphoramide catalyst.