Radicals 1,2-diphenylethane derivatives

Carbon-Carbon Bond Cleavage in Radical Cations of Diphenylethane Derivatives... 

Mesolytic cleavage in radical anions of 1,2-diphenylethane derivatives... 

A recent brief study of the photochemistry at 254 nm in tetrahydrofuran (THF) of the fluorinated 1,2-diphenylethane derivatives, 100, reported very low and inefficient conversions to the corresponding stilbene derivatives, Eq. (36) [138]. The addition of a radical inhibitor, 2,6-di-t-butyl-4-methylphenol, had no effect. The mechanism for the loss of hydrogen fluoride is therefore not known. Irradiation in the presence of LiAlHt gave reduction products and the mechanism proposed begins with electron transfer from the hydride to the excited state of the substrate to form a radical ion pair. 

It is noteworthy that the addition of a radical scavenger such as 2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) completely suppressed the reactivity, showing that a radical mechanism is most likely involved in the transformation. Furthermore, a significant amount of 1,2-diphenylethane was obtained under such standard conditions, which also supports the formation of a benzyl radical 6-D during the reaction (Scheme 4.6). Firstly, ferf-butyl peroxide decomposes to give a tert-butyl peroxide radical and oxidizes Fe(ii) 6-A into Fe(iii) 6-B, which reacts with the 1,3-dicarbonyl derivative leading to an Fe(iii) enolate 6-C. Meanwhile, a benzyl radical 6-D obtained by abstraction of H can then react with 6-C. 

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