Palladium-Catalyzed(4 + 3) Cycloadditions of Salicyliminesand 1,4-Enynes: Access to Benzazepines

Benzazepines represent a class of valuable nitrogen-containing heterocyclic compounds and widely applicable synthetic intermediates. Thus, the development of efficient and selective synthetic strategies for benzazepine construction via rational synthon design is of great research significance. Herein, we report the design of 1,4-enynes as novel trimethylenemethane (TMM) precursors and their application in palladium-catalyzed (4 + 3) cycloaddition reactions. This transformation proceeds efficiently at room temperature, affording a variety of benzazepine derivatives in good yields with excellent chemoselectivity. The practicality of the developed methodology is verified by gram-scale synthesis. Moreover, the obtained benzazepine products can be readily transformed into oxepine derivatives and triazole derivatives, and can undergo intramolecular cyclization under gold catalysis. This work demonstrates that bench-stable 1,4-enynes can serve as innovative precursors for palladium-catalyzed TMM-involved allylic cycloaddition reactions, and highlights their broad synthetic utility.