Synthesis of Benzazepinones via Intramolecular Cyclization Involving Ketene Iminium Intermediates

Herein, we describe a very straightforward and metal free method for the synthesis of benzazepinones through an intramolecular cyclization. This involves an ortho-vinyl-anilino-amide as starting material which is converted to a keteniminium intermediate that spontaneously cyclize to form a 7-membered ring iminium. Under slightly basic hydrolysis conditions, this latter is ultimately converted to the desired benzazepinone. Control experiments on the electron density of the nitrogen constituting the aniline were performed to support our proposed mechanism and rationalize the selectivity of the reaction.