Photolysis of 2,6-diphenyl-4h-pyran-4-thione and 2,6-diphenyl-4h-thiopyran-4-thione

Photolysis of 2,6-diphenyl-4H-pyran-4-thione and 2,6-diphenyl-4H-thiopyran-4-thione resulted in desulfurization and furnished 2,2′,6,6′-tetraphenyl-4,4′-di(pyranylidene) and 2,2′,6,6′-tetraphenyl-4,4′-di(thiopyranylidene) as the products. The mechanism was studied by quantum yield measurements. In dioxane, the quantum yield of di(pyranylidene) formation was concentration-dependent, while in benzene, it was independent of the concentration. The photoreaction proceeds via the triplet state of 2,6-diphenyl-4H-pyran-4-thione and 2,6-diphenyl-4H-thiopyran-4-thione and the H atom abstraction from solvents appears to be a key step in the formation ofdi(pyranylidene).