Diels–Alder reactions of heterocyclic fused [alpha]-pyrones

The chemistry of heterocyclic analogues of orthoquinodimethane is reviewed. Benzothieno[2,3-c]pyran-3-ones and the isomeric [3,2-c]pyranones are stable analogues of benzothiophene-2,3-qyinodimethane. When heated with alkynes they undergo Diels-Alder reaction to give, after loss of carbon dioxide, dibenzothiophenes. [Continues.]