The intermediate ethyl indole-4-carboxylate(3) was obtained from 2-methyl-3-nitrobenzoic acid(1) as raw material by esterification under the catalyst of acid,it was then condensed with N,N-dimethylformamide diethyl acetal,reduced with iron and acetic acid.

Synthesis of ethyl 3-formylindole-4-carboxylate;