SENSITIZED PHOTOCYCLODIMERIZATION OF α,β-UNSATURATED CYCLIC SULFONES. CRYSTAL STRUCTURAL ANALYSES OF THE PHOTODIMERS OF 2-SULFOLENE AND THIA-2-CYCLOHEXENE-1,1-DIOXIDE

Article abstract of DOI:10.1016/S0040-4020(01)80031-4

The reactivity of five- and six-membered unsaturated cyclic sulfones in sensitized photocyclodimerization depends on position and substitution of the double bond.Thus, 2-sulfolene (1) and its six-membered analogue thia-2-cyclohexene-1,1-dioxide (3) photodimerize to yield each three products, 5, 6, 7 and 9, 10, 11, respectively, of which only 7 and 10 are analogous.However, 3-methyl-2-sulfolene (1a), 3-sulfolene (2) and its 3-methyl derivative (2a), as well as thia-3-cyclohexene-1,1-dioxide (4) remain unchanged under the same conditions.Dimerization of 1 and 3 is also effected by γ-irradiation.Structure and stereochemistry of the six dimers were determined by crystal structural analyses.Except for 6, the main product of γ-radiation-induced dimerization of 1, all the other dimers (5, 7 and 9-11) are tricyclic <2+2> cycloadducts with anti (transoid) configuration at the central cyclobutane ring. 6 is an unsaturated open-chain dimer with C-C and C-S bond contractions, the latter indicating conjugation of the double bond with the sulfone group.While the cyclobutane rings of 5 and 7 (from 1) are planar, those of all three dimers from 3 are folded: the 6.4.6 skeletons of two of them comprise one (11) or two (9) trans fusions.