Regioselective Bromination of Methoxy Derivatives of Ethyl Indole-2-carboxylate [Synthetic Studies of Indoles and Related Compounds. XXX]

Abstract

Bromination of ethyl methoxyindole-2-carboxylates(1) with bromine in acetic acid proceeded on the benzene moiety of 1, whereas the reaction of 1 with pyridinium bromide perbromide in pyridine or N-bromosuccinimide in dimethylformamide gave ethyl 3-bromo-methoxyindole-2-carboxylates ( 2 ) .Bromination is one of the fundamental reactions in indole chemistry.Although, bromination usually proceeds at the position,^ situation is not the same in methoxyindoles as shown in Scheme 1, because electrondonating group on benzene moiety tends to direct the bromine toward the benzene moiety.Indeed, bromination of ethyl 5-methoxyindole-2-carboxy- late (lb) with bromine in acetic acid was reported to occur3 on the Cqposition rather than the C3-position.In other words C3-bromination is not easy in methoxyindoles in usual cases, although the C3-bromination Scheme 1