Abstract Electron-rich 1, 1-diarylethylenes (1a–e) afford 3, 3, 6, 6-tetraaryl-1, 2-dioxanes (3a– e) in high yields (> 907%) when subjected to electron-transfer photooxygenation in the presence of DCA. Whereas 1, 1-diphenyl-ethylene (1f) and 1, 1-di (p-chlorophenyl) ethylene (1h) yield the 1, 2-dioxanes 3f and 3h at 30% and less than 10%, respectively, there is negligible (if any) 1, 2-dioxane formation with 1, 1-di (m-anisyl) ethylene (1i). 1, 2-Dioxane ...