Bromination of 4,6-dimethoxyindoles

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.