Preparation of Benzothiopyrano[2,3-b]- indoles by the Reaction of 1,3-Dihydro- indole-2-thiones with Certain Dienophiles

Benzothiopyrano[2,3-b]indoles were prepared by the cyclization of 1,3-dihydroindole-2-thiones with various dienophiles.The 1,3-dihydroindole-2thiones were readily synthesized by the reaction of oxindole with P 2 S 5 followed by a piperidine-mediated condensation of the resulting thioindole with a suitable aromatic aldehyde.