A rhodium-catalyzed coupling-cyclization reaction of alkenyldiazoacetates with o-alkenyl arylisocyanides has been developed. In this reaction, the highly reactive alkenylketenimine intermediates generated by coupling reaction of alkenyldiazoacetates with o-alkenyl arylisocyanides undergo intramolecular [4 + 2] cycloaddition and provide a novel, highly efficient method for the one-step synthesis of carbazoles by formation of three new bonds and two rings from readily available acyclic starting materials.