Enantioselective Diels–Alder Reaction of α‐Acyloxyacroleins Catalyzed by Chiral 1,1′‐Binaphthyl‐2,2′‐diammonium Salts

A diammonium salt of chiral 1,1′‐binaphthyl‐2,2′‐diamine ( 2a ) and trifluoromethanesulfonimide (Tf 2 NH) shows excellent catalytic activity and enantioselectivity for the Diels–Alder reaction of α‐acyloxyacroleins. For example, in the presence of 5 mol % of 2a and 9.5 mol % of Tf 2 NH, the Diels–Alder reaction of α‐(cyclohexanecarbonyloxy)acrolein with cyclopentadiene proceeded in EtCN at −75 °C to give the adducts in 88 % yield with 92 % exo and 91 % ee . The electron‐donating property of the acyl group of the α‐acyloxyacroleins increases the enantioselectivity due to the formation of strong intramolecular hydrogen bonding of the acyl group with a proton of the ammonium group in the transition state. This catalyst can be easily prepared in situ by mixing the commercially available chiral diamine and Tf 2 NH.