Photooxygenation of 1,2-Diaryltetrahydrobenziimidazole and Crystal Structure of Its Product

The reactions of 1-(4-methylsulfonylphenyl)-2-(2,5-chlorophenyl)tetrahydrobenziimidazole (1) with singlet oxygen has been investigated. Compound 1, from a initially formed 2,5-endoperoxide and the subsequence instable zwitterion intermediate, generated a dioxetane. The formed dioxetane through ring-opening and interior-ring electrophilic reaction and finally converted into a more stable seven-membered ring product which has not been reported before. The structure of the photooxygenation product was elucidated by X-ray analysis, H NMR, MS and elemental analysis. The compound 1,2-diaryltetrahydrobenziimidazole crystallizes in monoclinic, space group P2(1)/c with a = 18.533(4) (angstrom), alpha = 90(degrees); beta = 7.7658(16) (angstrom), beta = 91.96(3)(degrees); c = 14.203(3) (angstrom), gamma = 90(degrees); V = 2042.9(7) angstrom(3), Z = 4, F(000) = 948, D-c = 1.474 (g cm(-3)), C20H18N2O4SCl2, M-r = 453.39 and mu = 0.444 mm(-1).