Abnormal Fischer indolization and its related compounds. XXII. Fischer indolization of ethyl pyruvate 2-(2-chloro- and 2,6-dichlorophenyl)methylhydrazones.

This is the authors' abstract. We don't add key points for this paper.

The Fischer indolization of ethyl pyruvate 2-(2-chlorophenyl)methylhydrazone (17) with HCl/EtOH proceeded rapidly to give six 1-methylindoles, ethyl 7-chloro (19), 6-chloro (22), and unsubstituted (24)-1-methylindole-2-car-boxylates, and dichloro derivatives (21, 23, and 26), whereas no indolization had occurred with the correspinding NH-hydrazone, as described in a previous paper. This result shows that the abnormal Fischer indolization of 2-chloro-phenylhydrazones with HCl/EtOH occurred in an ortho-C6 fashion, in the same manner as that of the corresponding 2-methoxyphenylhydrazones (1 and 2).The Fischer indolization of ethyl pyruvate 2-(2, 6-dichlorophenyl)methylhydrazone (18) with HCl/EtOH did not occur at all, whereas the reaction with ZnCl2/AcOH gave a low yield of ethyl 5, 7-dichloro-3-methylindole-2-carboxylate (36), which was formed by migration of the N-methyl group during Fischer indolization.