Ethyl indole-2-carboxylate. ring synthesis

This ring closure takes place readily whenever the carbonyl and amino groups occur in the relative positions shown above. Reduction of o-nitro-phenylacetonitrile by stannous chloride produces indole rather than the corresponding amino aldehyde. The synthesis is most useful for the preparation of indole-2-carboxylic acid by reduction of o-nitrophenyl-pyruvic acid with ferrous sulfate and ammonia or with sodium hydrosulfite. The ethyl ester is obtained by a similar reduction with zinc and acetic acid or by catalytic hydrogenation of ethyl o-nitrophenyl-pyruvate over platinum oxide catalyst. ... 

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