Abstract
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 by reaction with sodium sulfide and oxidation. Pyrazole fused analogues 15 and 16 (R = Me and COPh) were prepared 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.
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