Addition reactions of heterocyclic compounds. Part XLVIII. Reactions of indoles with dimethyl acetylenedicarboxylate in the presence and absence of solvents
Treatment of indole with dimethyl acetylenedicarboxylate alone gave a mixture from which the major components tetramethyl carbazole-1,2,3,4-tetracarboxylate, tetramethyl 9-(cis-1,2-dimethoxycarbonylvinyl)-1,2-dihydrocarbazole-1,2,3,4-tetracarboxylate, trimethyl 5,6-dihydro-6-oxophenanthridine-7,8,9-tricarboxylate and dimethyl 2,3-dihydro-2-(indol-3-yl)benzazepine-3,4-dicarboxylate, and ten other indole derivatives, were isolated by chromatography and identified from their spectra. Fewer products were obtained when benzene or toluene was used as solvent; the main products in methanol and in acetic acid were, respectively, dimethyl indol-3-ylfumarate and dimethyl 2,2-di(indol-3-yl)succinate. Reactions involving 1- and 2-methylindole and diethyl acetylenedicarboxylate were also investigated.