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Abstract
The thermolysis of 2,5-diphenyl-1,4-dithiin-1-oxide (4) in the liquid phase induced rearrangement to 2-formyl-2,4-diphenyl-1,3-dithiole (7) and extrusion of sulfur oxide to give 2,4-diphenylthiophene (2a) as well as deoxygenation to 2,5-diphenyl-1,4-dithiin (1a). Distribution among the three products was dependent on the initial concentration; low concentration suppressed the deoxygenation. For the formation of the thiophene occurrence of two mechanisms, one involving bimolecular disproportionation and another via unimolecular valence isomerization, was suggested by the kinetic study as well as the solvent effect. The photolysis of (4) afforded (7) and another 1,3-dithiole isomer, 2-benzoyl-4-phenyl-1,3-dithiole (9) which was not obtained in the thermolysis. The rearrangements are discussed in terms of a radical mechanism. In the thermolysis of 2,5-diphenyl-1,4-dithiin-1-(N-tosyl)imide (6), no rearrangements were observed and thiophene (2a) due to the extrusion of a thionitroso moiety was obtained together with the deoxygenated parent dithiin (1a). On the other hand, the photolysis of (6) resulted in ring transformation to a 1,3-dithiole compound.