The electron transfer catalyzed photooxygenations and singlet oxygen sensitized reactions of 1, 5-dithiocyclooctane, 1, and 5H, 7H-dibenzo[b,g][1,5]dithiocin, 2, are compared.  This work was prompted by a recent suggestion that these reactions proceed via addition of oxygen to a sulfide radical cation. 

N-Methylquinolium tetrafluoroborate, 3, and 2-(p-methoxyphenyl)-4,6-diphenylpyrylium tetrafluoroborate, 4, were chosen as the electron transfer sensitizers and methylene blue, 5, was selected as the singlet oxygen sensitizer.  Detailed product, laser flash photolysis, kinetic isotope, electrochemical, and computational studies are used to construct alternative reaction pathways to the oxygen/sulfide radical cation route.