Palladium-catalyzed ring-opening of cyclopropyl benzamides: synthesis of benzo[c]azepine-1-ones via C(sp3)-H functionalization

A variety of difficult to obtain benzo[c]azepine-1-ones are synthesized via a novel palladium-catalyzed, silver-promoted intramolecular cyclization of cyclopropyl benzamides. This biologically important class of molecules is prepared in an efficient and high-yielding manner from easily accessible starting materials. Both aryl bromides and iodides are effective substrates for the transformation. Mechanistic studies indicate that the reaction proceeds through a cyclopropyl C(sp3)-H cleavage step, followed by ring-opening, deprotonation, and reductive elimination.