Novel regioselective photochemical transformation of 4-methyl-2,4,6-triphenyl-4H-thiopyran-1,1-dioxide

On photolysis of 4-methyl-2,4,6-triphenyl-4H-thiopyran-1,1-dioxide (1d) in chloroform solution with a low-pressure mercury lamp at lambda = 254 nm und er an argon atmosphere, a high regioselective rearrangement takes place via a gem-methylphenyl migration to yield two bicyclic stereoisomers anti-6-me thyl-1,3,6-triphenyl-2-thiabicylo[3.1.0]hex-3-ene-2,2-dioxide (anti-2d) and syn-6-methyl-1,3,6-triphenyl-2-thiabicyclo[3. 1.0]hex-3-ene-2,2-dioxide (s yn-2d). The results observed are discussed in the light of a thia-di-pi -me thane rearrangement through a vinyl-vinyl bonding interaction. (C) 2001 Pub lished by Elsevier Science B.V.