Preparation and Diels–Alder reactivity of benzothieno[2,3-c]- and benzothieno[3,2-c]-pyran-3-ones, benzothiophene-2,3-quinodimethane analogues; synthesis of dibenzothiophenes
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.