Synthesis of indole and related compounds from halo-nitroaromatics

5,7-Dimethyl-6-azaindole was synthesized by treatment of 3-amino-2,6-dimethyl-4-pyridineacetaldehyde diethyl acetal with hydrochloric acid in boiling ethanol. According to the similar manner, indole and ethyl 4-indolecarboxylate were obtained from the corresponding 2-aminophenylacetaldehyde derivatives in satisfactory yields. The starting materials were easily prepared by palladium-catalyzed cross-coupling reaction of o-halonitroaromatics with trimethylsilylacetylene followed by the reaction with sodium ethoxide and catalytic reduction of the o-nitro group.