Enantioselective aza-Diels–Alder reaction of Brassard’s diene with aldimines catalyzed by chiral N,N′-dioxide–Yb(OTf)3 complex

The chiral N,N′-dioxide–Yb(OTf)3 complex-catalyzed enantioselective aza-Diels–Alder reaction of Brassard’s diene with aldimines has been developed, giving the corresponding α,β-unsaturated δ-lactam derivatives in moderate yields with good enantioselectivities (up to 81% ee and up to 99% ee by single recrystallization) under mild conditions. Isolation of the reaction intermediate indicates that this asymmetric aza-Diels–Alder reaction proceeds through a stepwise Mannich-type pathway.