Modified cinchona alkaloid-catalysed enantioselective [4+4] annulations of cyclobutenones and 1-azadienes

Abstract

Constructing eight-membered rings, especially in an enantioselective manner, is a challenging task due to unfavorable enthalpic and entropic barriers of the transition states during the formation process. Here we report an asymmetric [4+4] annulation reaction of diverse 1-azadienes and β-substituted cyclobutenones under the catalysis of modified cinchona alkaloids, by the in situ generation of ring-opened ammonium dienolate intermediates. A spectrum of heteroarene- or indene-fused eight-membered lactams are obtained in fair to excellent yields with remarkable enantioselectivities (up to 99% yield, 99% ee).