Abstract
Fischer indolization of ο-methoxyphenylhydrazone derivatives provides various types of unexpected indole products under several condition. These abnormal results were well-established. The representative case has been shown by the formation of ethyl 6-chloro- and 6-ethoxyindole-2-carboxylate in treatment of ethyl pyruvate 2-methoxyphenylhydrazone with ethanolic hydrogen chloride. Formation of these products are explainable by cyclization of the starting hydrazone to the orthoposition occupied by a methoxy group. This abnormal Fischer indolization has been developed to a new synthetic method for 6-substituted indole. For example, treatment of 2-methoxyphenylhydrazone with TsOH in the presence of ethyl acetoacetate, an enolizable dicarbonyl compound, gave an indolic product having ethyl acetoacetate group at the C6 position with other indole derivatives. The new reaction was applied to synthesis of two natural indole products having an alkene side chain at the C6 position.Fischer indolization of other ortho substituted phenylhydrazones have been studied.
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