Abstract
The benzothieno[2,3-c]pyran-3-ones (6) and the isomeric [3,2-c] pyranones (7) are stable analogues of benzothiophene-2,3-quinodimethane (3). When heated with alkynes they undergo Diels-Alder reactions to give, after loss of carbon dioxide, dibenzothiophenes. The regiochemistry of the Diels–Alder reaction is discussed.