Asymmetric Syn -Selective Vinylogous Addition of Butenolides to Chromones via Al-Li-BINOL Catalysis.

A gram-scale syn -selective asymmetric vinylogous addition of butenolides to chromones, catalyzed by an Al-Li-BINOL (ALB) complex, was developed in this study. For various combinations of substrates, the observed diastereoselectivity approached 20:1 with 84-98% ee. This protocol is complementary to previously reported ones and improves the selectivity for several chromones. This methodology can be applied to a quinolone substrate, affording another type of heterocyclic scaffolds substituted with five-membered lactones. Computational studies support the role of ALB as a bifunctional catalyst in this reaction and provide insights into the origin of the observed stereoselectivity.