Iodine-Catalyzed Oxidative Coupling between Indoles and Benzylamines: A Greener Method to Bis(indolyl)methanes

Metal-free synthesis of bis(indolyl)methanes involving oxidative coupling of indoles with benzylamines in the presence of iodine as a catalyst under an air atmosphere has been demonstrated. This method provides an attractive and efficient approach to a variety of functionalized bis(indolyl)methanes under mild conditions. Ostensibly, iodine promotes the electrophilic substitution of indoles with imines that were generated from benzylamines by self-coupling, to produce bis(indolyl)methane compounds. Previously, our laboratory also reported a first approach for the synthesis of bis(indolyl)methanes by iron-catalyzed oxidative coupling of benzylamines with indoles. The feasibility of a large-scale reaction was tested, and found that the reaction proceeds without any significant loss of its efficiency. Furthermore, the synthetic utility of the transformation was successfully demonstrated by preparing several biologically active compounds.