Chiral 1,1′-binaphthyl-2,2′-diammonium salt catalysts for the enantioselective Diels-Alder reaction with α-acyloxyacroleins

A diammonium salt of chiral 1,1′-binaphthyl-2,2′-diamine and trifluoromethanesulfonimide (Tf₂NH) shows excellent catalytic activity and enantioselectivity for the Diels-Alder reaction of α-acyloxyacroleins with cyclic dienes. For example, in the presence of 5 mol % of the ammonium catalyst, 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. This catalyst can be easily prepared in situ by mixing the commercially available chiral diamine and Tf₂NH.