2. 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 P. Mark Jackson,Christopher J. Moody J. Chem. Soc. Perkin Trans. 1 1990 681