Dry reaction of indoles with carbonyl compounds on montmorillonite K10 clay: a mild, expedient synthesis of diindolylalkanes and vibrindole A

Dry reaction of indoles 1a–c with aldehydes 2a–i, ketones 2j–o and an acetal 2p on M. K10 clay at room temperature furnished 3,3′-diindolylalkanes (DIAs: 3a–h, j–r). The novel formation of tris(3-indolyl)methane 4 from 2i through tandem reactions and of the DIAs 6 and 8 from 1d through Plancher rearrangements were also observed.