An approach to the novel stereoselectivity in photorearrangement of 4,4-dialkyl-2,6-diphenyl-4H-thiopyran-1,1-dioxides

The photochemical behaviour of 4,4-dimethyl-, 4-tert-butyl-4-methyl- and 4-benzyl-4-methyl-2,6-diphenyl-4H-thiopyran-1,1-dioxides has been investigated and compared with those of 4-methyl-2,4,6-triphenyl-4H-thiopyran-1,1-dioxide and 2,4,4,6-tetraphenyl-4H-thiopyran-1,1-dioxide as model compounds under identical experimental conditions followed by 1H NMR spectroscopy. The high yields of the stereoisomeric bicyclic photoproducts of dialkyl analogues in the absence of SO2 extruded byproducts are discussed on the basis of a vinyl–vinyl di-π-methane (DPM) rearrangement.