Sequential Ag(I) Salt and Chiral N-Heterocyclic Carbene Catalysis Enables Enantioselective and Diastereoselective Construction of Complex Heterocyclic Molecules and the Switch of Stereoselectivity.

Abstract

Organic reactions under cascade catalysis provide a powerful strategy to construct molecules of complexed structures. Reported herein is the sequential silver(I) salt and chiral N-heterocyclic carbene (NHC) catalyzed enantioselective and diastereoselective synthesis of a diversity of unprecedented fused heterocyclic compounds from the reactions of readily available N'-((2-alkynyl-3-pyridinyl)methylene)hydrazides with 2-aroylvinylcinnamaldehydes. Both reaction pathways and stereoselectivity were steered conveniently and efficiently by the employment of different NHCs and bases, enabling the selective preparation of pentacyclic ring-fused 1,6-naphthyridine derivatives and 1,6-naphthyridine-substituted tricyclic products in moderated to good yields with high enantioselectivity and diastereoselectivity. Mechanisms accounting for the selective transformations, especially the effect of base and chiral NHC catalyst on the reaction course and stereochemistry of products, were also discussed.