Mechanistic Insights into the BINOL-Derived Phosphoric Acid-Catalyzed Asymmetric Allylboration of Aldehydes

Abstract

BINOL-derived phosphoric acids catalyze the asymmetric allylboration of aldehydes. DFT and QM/MM hybrid calculations showed that the reaction proceeds via a transition state involving both a hydrogen-bonding interaction from the catalyst hydroxyl group to the pseudoaxial oxygen of the cyclic boronate and a stabilizing interaction from the phosphoryl oxygen of the catalyst to the formyl hydrogen of the aldehyde. These interactions lower the energy of the transition structure and provide extra rigidity to the system. This mechanistic pathway is consistent with the experimentally observed enantioselectivity except in one case. We have used our model's predictions to guide our own experimental work. The conflict is resolved in favor of our calculations.