Competitive Photochemical Pathways in the Rearrangement of Tetrasubstituted 4H-Thiopyrans

Summary. The photoisomerization of 4,4-dialkyl-2,6-diphenyl-4H-thiopyrans and 4-benzyl-2,4,6-triphenyl-4H-thiopyran was investigated and compared with those of the 2,4,4,6-tetraaryl- and 4-alkyl-2,4,6-triaryl-4H-thiopyran analogues reported earlier. Obviously, the alkyl groups at the 4-positions of the 4H-thiopyrans strongly diminish the efficiency of the di--methane rearrangement and, contrastingly, a four-electron suprafacial [1,3]-sigmatropic rearrangement is found to be highly efficient.