Abstract
Bromination of 2-ethylthioindoles (6a, c) and 2-bromoindole (6e) with N-bromosuccinimide (NBS) in carbon tetrachloride gave 3-bromoindolenines (8). On the other hand, bromination of 2-ethylsulfonylindoles (6b, d) with NBS in methylene chloride gave 1-bromoindoles (7b, d) which were converted to 8 on heating. Both 1-bromoindoles and 3-bromoindolenines act as brominating agents for skatole or 3-phenylindole. Heating of 3-bromo-2-ethylthio-3-phenylindolenine (8c) in carbon tetrachloride gave the 6-bromoindole (11), while the 2-ethylsulfonyl derivative (8d) gave 5-bromoindole (13). However, 2, 3-dibromo-3-phenylindolenine (8e) in acetic acid was converted to 6-bromo-(main) (17) and 5-bromoindole (18) (minor). 3-Bromoindolenines (8a, b, d) gave the oxindoles (19) accompanied with the migration of the 2-substituent on treatment with ethanolic hydrochloric acid, while some 3-alkoxyoxindoles (21, 22, 23) were obtained on treatment with alcohol and base. On the other hand, the 1-bromoindole (7b) was converted to the indole (6b) under various conditions.
