A facile clay-mediated synthesis of 3,3-diindolyl-2-indolinones from isatins

Abstract

Dry reaction of isatins (3a, 3b) with indoles (4a-e) on montmorillonite K10 clay at room temperature furnished within minutes 3,3-bis(3'-indolyl)-2-indolinones (1a-f) in high yields. 5-Nitroisatin (3c) furnished, in addition to the expected indolinone 1h, 3-hydroxy-3-(3'-indolyl)-5-nitro-2-indolinone (6), a likely intermediate to 1h.