Abstract The polar 1, 4-cycloaddition of sulfene to N, N-disubstituted 5-aminomethylene-1, 5, 6, 7-tetrahydro-1-methylindol-4-ones occurred only in the case of aliphatic N-substitution to give, generally in good yield, 4-dialkylamino-3, 4, 5, 6-tetrahydro-7-methyl-7H-1, 2-oxathiino [6, 5-e] indole 2, 2-dioxides IV. Full aromatization of IVa (4-NR 2= dimethylamino) with DDQ in refluxing benzene gave in low yield 7-methyl-7H-1, 2-oxathiino-[6, 5-e] indole 2, 2- ...