Catalytic Enantioselective Allylation of Dienals through the Intermediacy of Unsaturated π-Allyl Complexes

Abstract

The nickel-catalyzed enantioselective addition of allylboronic acid pinacol ester [allylB(pin)] to alpha,beta,gamma,delta-unsaturated aldehydes is described. This reaction results in a remarkable inversion of substrate olefin geometry, providing the Z,E-configured reaction product in good enantioselectivity and olefin stereoselectivity. The reaction appears to proceed by conversion of the dienal to an unsaturated pi-allyl complex followed by reductive elimination via transition state II. Enantioselectivities range from 73-94% ee for a range of delta-substituted dienals when chiral ligand L3 is employed.