Supported Iridium Catalyst for the Green Synthesis of 3,3′-Bis(indolyl)methanes Using Methanol As the Bridging Methylene Source

The first example of a heterogeneous catalyst based on hydrotalcite-derived Mg-Al oxides supported iridium (Ir/MgxAlO) for activation of methanol in the synthesis of bis(indolyl)methanes (BIMs) is reported. In this clean and reusable iridium-based catalytic system, a variety of substituted indoles were selectively converted to their corresponding BIMs in moderate to good yields with high tolerance to reducible functional groups by using methanol as a bridging methylene (-CH2-) donor. The high catalytic activity and selectivity of the reaction benefit from the delicate cooperation of redox/acid-base surface sites on this artificially designed multifunctional Ir/MgxAlO catalyst. The overall simplicity, chemoselectivity and sustainability of the catalytic system make this approach a valuable and step-economical tool to construct C-C bond directly from methanol in the synthesis of more complex molecules.