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Four 7-cyano-indoles and one 2-cyano-indole have been synthesized from the related aldoximes, via the intermediate 2,4-dinitrophenyl oxime ethers.

The bromination of activated 4,6-dimethoxyindoles can be carried out effectively provided that an electron-withdrawing group is also present. Thus the range of products includes 2-bromo-7-formyl or 2-bromo-7-acetylindoles 13a-c and 16, 7-bromo-2-acetylindole 21, 2,5-dibromo-7-acetylindole 17, 2,5-dibromo-N-sulfonylindole 27, and 2,7-dibromo-N-acetylindole 24. Acetyl and sulfonyl protecting groups on nitrogen can be removed to give 2-bromoindoles 28a-b, 2,5-dibromoindole 29, and 2,7-dibromoindole 4. (C) 2012 Elsevier Ltd. All rights reserved.

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.

A range of 3-substituted-4,6-dimethoxyindoles bearing electron-withdrawing groups in either the 2- or 7-position, can be nitrated using nitric acid adsorbed on silica, to give 7-nitro and 2-nitro-indoles, respectively. A 1-cyano-indole gives regioselectively the 2-nitro-indole with loss of the cyano group.