Chlorination of 2-Methyl- and 2-Phenylindole with NaOCl. Formation of Intermediates and Their Reactions with Alkaline Methanol

Chlorination of 2-methylindole (1) in carbon tetrachloride with excess sodium hypochlorite gave a 2:1 mixture of N,3-dichloro-2-methylindole (4) and 3,3-dichloro-2-methyl-3H-indole (5) in a total yield of 76-92%. N-Chloro-2-methylindole (2) was detected when the chlorination was carried out with an indole to NaOCl ratio of 10:1. Sodium hypochlorite was found to promote the rearrangement of N-chloroindoles 2 and 4. The chlorination of 2-phenylindole (6) gave a mixture of N,3-dichloro-2-phenylindole (8) and 3,3-dichloro-2-phenyl-3H-indole (9) in a total yield of 81-92%. The rearrangement of 8 to 9 was detected by IR and UV. This occurred in the presence or absence of NaOCl. Reactions of the dichloro intermediates with alkaline methanol gave a number of products. It is proposed that the N,3-dichloroindoles rearranged to their respective 3H-indoIes in alkaline methanol and the products were formed by nucleophilic attack on either carbon (C-3) or chlorine of the 3H-indole.