| Popis: |
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 formation proceeds in a chain reaction (Scheme 1). N-Vinylcarbazol (1g), however, yields the 1,2-dioxane 3g via the cyclobutane derivative 7 (Scheme 2). |
