NH4Cl-promoted synthesis of symmetrical and unsymmetrical triindolylmethanes under solvent-free conditions

The synthesis of various triindolylmethanes from indole-3-carboxaldehyde, using indole derivatives as reactants and NH4Cl as catalyst under solvent-free conditions, is described. This methodology provides access to both symmetrical and unsymmetrical triindolylmethanes in excellent yields. With N-methylindole particularly, indole-3-carboxaldehyde appears to act as a formyl donor, leading to the exclusive formation of a symmetrically trisubstituted product. The novelty of the methodology lies in its operational simplicity, environment friendly reaction conditions, and inexpensive and easy availability of the catalyst. A plausible mechanism of formation of the products is suggested.