Ethyl 6-azaindole-3-carboxylate (I) was formylated using dichloromethyl methyl ether and AlCl3 to provide aldehyde (II). Nitrogen protection in (II) with benzenesulfonyl chloride and NaH gave sulfonyl derivative (III). Subsequent Wittig condensation of (III) with (ethoxycarbonylmethylene)triphenyl phosphorane produced the unsaturated ester (IV). Finally, removal of the benzenesulfonyl protecting group of (IV) was effected by treatment with ethanolic NaOEt.