Highly enantioselective palladium-catalyzed umpolung allylation of aldehydes

Abstract

Compared with well-established electrophilic π-allylpalladium chemistry, the catalytic asymmetric reactions via umpolung of π-allylpalladium have received limited success. Although extensive efforts have been devoted, only modest enantioselectivities have been obtained in the palladium-catalyzed asymmetric umpolung allylation reactions. In this context, we disclose a highly enantioselective palladium-catalyzed umpolung allylation of aldehydes with allylic alcohols and their derivatives. By using sterically hindered chiral monodentate spiro phosphite ligands, we have accomplished the asymmetric allylation reaction with high yields and excellent enantioselectivities (up to 97% ee). These results represent the highest level of enantioselectivity for the umpolung allylation reactions. The present palladium-catalyzed asymmetric allylation reaction uses readily available allylic alcohols and their derivatives instead of sensitive allylic organometallic reagents, which provides a competitive alternative approach for preparation of versatile chiral homoallylic alcohols. A preliminary mechanism of palladium-catalyzed umpolung allylation reaction was discussed based on the experimental observations.