Synthesis of β- and γ-Carbolines by the Palladium/Copper-Catalyzed Coupling and Cyclization of Terminal Acetylenes ZhangHaiming LarockRichard C. 2002 A variety of 3-substituted β<i>-</i> and γ-carbolines have been synthesized from <i>N</i>-substituted 3-iodoindole-2-carboxaldehydes and 2-bromoindole-3-carboxaldehydes, respectively. The coupling of these aldehydes with various terminal acetylenes with PdCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>/CuI as the catalyst readily affords the corresponding alkynylindole carboxaldehydes, which have subsequently been converted to the corresponding <i>tert</i>-butylimines and cyclized to β<i>-</i> and γ-carbolines by either copper-catalyzed or thermal processes.