Iron-Catalyzed Synthesis of Indenones through Cyclization of Carboxamides with Alkynes

The iron/diphosphine-catalyzed annulation of a carboxamide possessing a bidentate directing group with an internal alkyne proceeds in the presence of phenylzinc halide as a base at 40 degrees C to produce a variety of indenone derivatives. The reaction proceeds through iron-catalyzed C-H bond activation of the carboxamide, followed by insertion of the alkyne into the resulting iron intermediate, and cyclization accelerated by the presence of Lewis acidic Zn-II. The reaction of naphthalene and anthraceneamide yields pi-conjugated indenone derivatives.