Heterocyclic fused 2,5-dihydrothiophene S,S-dioxides as precursors to heterocyclic o-quinodimethanes

Article abstract of DOI:10.1016/S0040-4020(01)80480-4

2,5-Dihydrothiophene 5,5-dioxides 8 and 6 have been obtained by interception of flash-pyrolytically produced 2,3-dihydro-2,3-bis(methylene)thiophene with sulfur dioxide and from methyl 4,5-bischloromethylthiophene-2-carboxylate from 3-phenylsulfonyl-2,5-dihydrothiophene S,S-dioxide by cycloaddition of diazomethane, base induced aromatisation and N-substitution of the sulfone 14. Reaction of 3-acetyl-4-phenylthio-2,5-dihydrothiophene S,S-dioxide with hydrazine and interception of 1-methyl-4,5-dihydrobis(methylene)pyrazole also gave pyrazole fused sulfones. On heating at 200°C, the heterocyclic fused sulfones underwent extrusion of sulfur dioxide and the resulting heterocyclic o-quinodimethanes were trapped with a range of dienophiles.