Amide-Based Morita–Baylis–Hillman Carbonates for Phosphine-Catalyzed Asymmetric (4+2) Annulation†

Abstract

Chiral phosphine-catalyzed asymmetric (4+2) annulation of the amide-based Morita–Baylis–Hillman (MBH) carbonates with β,γ-unsaturated butenolides has been developed to give enantiomer-enriched bicyclic δ-lactam γ-butyrolactone compounds. The amide-based MBH carbonates were first used as acceptor and aza-C4 synthon in phosphine catalysis. Under mild reaction conditions, a variety of amide-based MBH carbonates and unsaturated butenolides were well tolerated to provide chiral bicyclic δ-lactam γ-butyrolactone derivatives in high yields with excellent enantioselectivities as well as diastereoselectivities. A plausible reaction mechanism was also proposed based on control experiments and DFT calculations.