Photochemical [3+2] Cycloaddition of 2'-Vinyl-2H-1, 4-benzothiazin-3(4H)-one-2-spirocyclopropanes Catalyzed by Diphenyl Dichalcogenides

2'-Vinyl-2H-1, 4-benzothiazin-3(4H)-one-2-spirocyclopropanes (1) were irradiated with a tungsten lamp at room temperature in the presence of a catalytic amount of diphenyl dichalcogenide to provide 1, 2-dioxolane derivatives (3) in good yields. Diphenyl diselenide was more effective than diphenyl disulfide as a radical source. The photochemical [3+2] cycloaddition of 1b with electron-deficient alkenes proceeded smoothly under reflux in benzene to give spiro-cyclopentanes (5). Spiro-cyclopentenes (6) were formed by the photochemical [3+2] cycloaddition of 1b with alkynes.