Construction of Novel Tricyclic Fused-Ring Systems by the Multicomponent Reactions of Imidazo[1,5-a]pyridine Carbenes with Aromatic ortho-Dialdehydes and Electron-Deficient Alkynes

The multicomponent reactions of imidazo[1,5-a]pyridine carbenes with heterocyclic ortho-dialdehydes and electron-deficient alkynes were studied. While imidazo[1,5-a]pyridin-3-ylidenes reacted with furan-3,4-dicarbaldehyde and dimethyl acetylenedicarboxylate or dibenzoylacetylene to produce multifunctional difuro[3,2-b: 3',4'-d] azepines, the reaction of imidazo[1,5-a] pyridin-3-ylidenes with thiophene-3,4-dicarbaldehyde and activated alkynes afforded furo[3,2-b] thieno[3,4-d] azepine derivatives. This work not only provides two new types of tricyclic fused azepines, but also extends the applications of multicomponent reactions of N-heterocyclic carbenes in the construction of complicated fused-ring systems.