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• 28358-60-3 1-methoxy-2-[1-(2-methoxyphenyl)ethenyl]benzene 

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Substituent-Dependent Electron-Transfer Induced Photooxygenation of 1,1-Diarylethylenes

Rates and products of 9,10-dicyanoanthracene-sensitized photooxygenations of 1,1-diarylethylenes (1a-r) in acetonitrile were studied.If at least one of the aryl groups carries an electron-donating substituent at the para (or ortho) position (1a-l), 3,3,6,6-tetraaryl-1,2-dioxanes (2a-l) are generated in high yields (85-100percent).Benzophenones (3) are the only other observable products. 1,1-Diphenylethylene (1n) and its m-methoxy (1m), p-chloro (1o,p), and p-nitro (1q,r) derivatives, however, yield mainly benzophenones (3m-r) (>50percent) (the p-nitro compounds only in the presence of biphenyl). 1,2-Dioxanes (2m-p), cyclobutanes (4n-p), and α-tetralones (5m-o) are obtained as side products.Dioxanes, benzophenones, and α-tetralones are products of electron-transfer induced oxygenations involving triplet ground-state molecular oxygen, 3O2.Singlet molecular oxygen, O2(1Δg), contributes to the benzophenone formation from strongly electron-donor substituted diarylethylenes.An exception is the most powerful electron-donor substituted diarylethylene 1a, with which O2(1Δg) undergoes an electron-transfer reaction affording dioxane 2a.Dioxane formation proceeds via free-radical cations 1.+, which enter into a chain reaction with 1, 3O2, and another molecule of 1 to yield dioxane 2 and a new radical cation 1.+ that maintains the chain reaction.The efficiency of this chain process, however, is found to be several orders of magnitude smaller than expected.To explain this result, a 1,6-biradical .1-1-O2. is proposed to be generated in this chain reaction as the product-determining intermediate that predominantly fragments into 3O2 and two molecules of 1.Cyclization to dioxane 2 and transformation to benzophenone 3 occur at presumably less than 0.1percent from this biradical.The pathways leading to cyclobutanes (4) and α-tetralones (5) are also discussed.

FORMATION OF 1,2-DIOXANES BY ELECTRON-TRANSFER PHOTOOXYGENATION OF 1,1-DISUBSTITUTED ETHYLENES

Electron-rich 1,1-diarylethylenes (1a-e) afford 3,3,6,6-tetraaryl-1,2-dioxanes (3a-e) in high yields (>90percent) when subjected to electrontransfer photooxygenation in the presence of DCA.Whereas 1,1-diphenylethylene (1f) and 1,1-di(p-chlorophenyl)ethylene (1h) yield the 1,2-dioxanes 3f and 3h at 30percent and less than 10percent, 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).