6-bromo- (87, 6%), and 2-bromo-5-iodo-1-methoxyindole-3-carboxylic acids (88, 5%) together with unreacted 81 (16%).

The above results show that the bromination of 78 proceeds regioselec-tively at the 6-position, while the introduction of a methoxy group onto the 1-position changes the positional reactivity and tends to favor the 2-position.

Friedel-Crafts acylation of 77b with chloroacetyl chloride and AlCl3 in nitrobenzene provides cleanly methyl 5-chloroacetyl- (90a, 52%) and 6-chloroacetyl-1-methoxyindole-3-carboxylates (91a, 20%) with the ratio of 2.5 : 1 (Scheme 11) [28]. Under similar reaction conditions, Nakatsuka and co-workers reported the chloroacetylation of methyl 1-methylindole-3-carboxylate (89) to give 90b and 91b in the ratio of 3: 1 [29]. Comparing these results with ours, it would be safe to conclude that the introduction of a methoxy group onto the N(1) prefers the 6- to 5-substitution in Friedel-Crafts acylation.

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Scheme 11 Chloroacetylation of methyl indole-3-carboxylates

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