Enantioselective Ene Reaction Catalyzed by a Diphenylprolinol Silyl Ether

Significance

The first enantioselective intermolecular ene reaction that uses cyclopentadiene 1 as an ene component and α,β-unsaturated aldehydes 2 as the enophile is described. Diphenylprolinol silyl ether 3 was used as a catalyst, leading to cyclopentadiene products 4 and 5 in high yields and good enantioselectivities. The authors proposed the primary formation of a 5-substituted 1,3-cyclopentadiene product, which then isomerizes to give the 1- and 2-substituted isomers (4 and 5).