Photoinduced Reactions. XLII. Homolytic Expulsion of 4-Substituent in the Photochemical Reaction of 2,5-Cyclohexadienones

Abstract

Irradiation of 2,4,6-tri-t-butyl-4-bromo-2,5-cyclohexadienone (X) in various solvents yielded 2,4,6-tri-t-butylphenol (XIII) in high yields. It was shown that 2,4,6-tri-t-butylphenoxy radical (XII) was formed as an intermediate and that the light of shorter wavelengths than 450 mμ accelerated the hydrogen abstraction of XII. The rate of the photochemical decomposition of X decreased in the order: n-hexane, N,N-dimethylformamide and acetic acid. This and the sensitized reaction suggest that the formation of XII from X may result from the n-π^* triplet state of X. On the other hand, irradiation of 2,4,6-tri-t-butyl-4-nitro-2,5-cyclohexadienone (XI) afforded 2,6-di-t-butyl-p-quinone (XV) and 2,4,6-tri-t-butylphenol (XIII), indicating a homolytic cleavage of the C–NO₂ bond.