4,6-Dimethoxy-2,3-diphenylindole (1) undergoes acylation, bromination, oxidative coupling and acid-catalysed addition to aldehydes at C-7 to produce a range of 7-substituted indoles (3-11), the indolo-isatin (6), the 7,7′-bi-indolyls (14), (16), (18), and the 7,7′-di-indolylmethanes (20-31). Addition to cyclopentanone gave compound (32), while Michael addition to α,β-unsaturated ketones gave compound (33) and the non-benzenoid double adduct (34). Related reactions led to the formation of the ring-fused indoles (39) and (41). Some reactions of the related indole diester (2) are also reported. © 1994.
Black, D. S. C., Bowyer, M. C., Catalano, M. M., Ivory, A. J., Keller, P. A., Kumar, N., & Nugent, S. J. (1994). Substitution, oxidation and addition reactions at C-7 of activated indoles. Tetrahedron, 50(35), 10497–10508. https://doi.org/10.1016/S0040-4020(01)89590-9