2.5- Dihydrothiophene, irradiation

Unsaturated cyclic sulfones, e.g. 4,5-dihydrothiophene 1,1-dioxide and 3,4,5,6-tetrahy-drothiopyran 1,1-dioxide, afford mixtures of tricyclic dimers, both in sensitized irradiations and in [60Co] y-irradiation.23... 

Dihydrothiophene-3,4-dicarboxylic esters are thermally stable but photolabile (74JOC2366). Irradiation of the (rans-2,5-disubstituted derivative (563) results in quantitative isomerization to the unstable vinyl episulfides (564) and (565), probably via a biradical intermediate these are efficiently transformed by triphenylphosphine to the (Z,E)- and (E,E)-dienes respectively (Scheme 219). 

Direct irradiation of 2,5-dihydrofuran (175) results in the formation of furan, tetrahydrofuran, and the isomeric oxiran (176).146 Certain 2,5-dihydrothiophen derivatives are similarly converted to the corresponding vinylthiirans,147 whereas 5,5-diaryl-2,5-dihydrofurans are reported to undergo di-7i-methane rearrangement.148 An unexpected transannular phototransformation has been observed on irradiation of the l,3-dioxolen-2-one (177)... 

The irradiation of 2,5-dihydrothiophene derivatives in /(-hexane or ether at 254 nm of degassed solutions leads to rapid formation of thermally and photochemically unstable products. 

Irradiation of 2,3-dihydrothiophene-1,1-dioxide (>280 nm) in the presence of acetone as the photosensitizer gives the head-to-tail dimer (307) (16%) and the head-to-head dimer (308) (8.5%)... 

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