Dithiin

Dithiin, tetraphenyl-dication salt, 3, 968 half-wave potential, 3, 968 synthesis, 3, 982... 

Tile photolysis (A = 365 nm) of 42 alone resulted in a very slow conversion to the 1,4-dithiin 259, whereas the irradiation in the presence of nor-bornene quickly produced 260 in 95% yield (88CL657).Tlierefore, the conversion of 42 to 261 (or 262) and sulfur atom should be reversible. Tlie photolysis of 263 in 3-methylpentane at 77 K yielded a mixture of 261 and 262, as suggested by the electronic spectrum, which showed two absorption maxima at 580 and 370 nm (89TL2955). Similar results were also obtained for selenium species (88CL657 89TL2955). 

Kobayashi and Mutai75 have recently reported an interesting rearrangement of the 1,4-dithiin sulfone (53) to the thiophenes (54) and (55) (equation 12). While 54 presumably arises as a result of simple photoextrusion, the rearranged thiophene (55) is postulated to arise via the valence isomer (56), followed by cyclization to the thiophene, concomitant with, or preceded by, loss of S02. Some support for the intermediacy of the thioketone (56) was revealed by the isolation of the pyrrole (57), when the photolysis was conducted in n-butylamine. Compound 57 presumably arises by cyclization of the iV-butylimine analog of 56 initially formed. 

Fused 1,4-dithiins are formed when the 1,8-diketones derived from dithiols and a-bromoketones are treated with Lawesson s reagent (LR) <96TL2821>. 

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