Greatly enhanced enantioselectivity by an apparently remote steric effect in the 1,1′-binaphthyl-catalyzed alkynylzinc addition to aldehydes

An unusual steric effect in the binaphthyl-catalyzed asymmetric alkynylzinc addition to aldehydes is observed. Increasing the steric bulkiness at the para-position of the 3,3′-anisyl groups of the 1,1′-binaphthyl ligands, though apparently remote from the Lewis acid coordination sites, has greatly enhanced the enantioselectivity as well as catalytic activity. Propargyl alcohols with ees up to 92% have been produced from the reaction of a terminal alkyne with aromatic aldehydes by using the binaphthyl catalysts.