Novel clay-mediated, tandem addition–elimination-(Michael) addition reactions of indoles with 3-formylindole: an eco-friendly route to symmetrical and unsymmetrical triindolylmethanes

Dry reaction of 3-formylindole (1) with indole (2a) on Montmorillonite K10 clay at room temperature furnished within minutes tris(indol-3-yl)methane (3a) in high yield. The reaction of 1 with other mono- and dialkylindoles (2b–c, skatole, 8a–c) under similar conditions yielded either or both of symmetrical (3b–c, 9) and unsymmetrical (4b–c, 5b–c, 10, 11a–c) triindolylmethanes.