Photoinduced Reactions. XLIII. Photochemical Reactions of 4-Hydroxy-2,5-cyclohexadienones

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Abstract
Irradiation of 2,4-di-t-butyl-4,5-dihydroxy-2,5-cyclohexadienone (V) in methanol afforded a β-diketone (VIII) in a 68% yield. Diketone VIII was also formed on photolysis of a suspension of V in petroleum ether (62%) and an aqueous alkaline solution of V (56%). Photolysis of 2,4-di-t-butyl-4-hydroxy-5-methoxy-2,5-cyclohexadienone (VI) in various solvents yields IXa as a main product. On irradiation of VI in methanol, XI which might be formed by the addition of methanol to IXb was also isolated. Irradiation of 2,4,6-tri-t-butyl-3-methoxy-4-hydroxy-2,5-cyclohexadienone (VII) in a variety of solvents gave a cyclopentadienone (XIII) in high yields. It is reasonable to assume that the cyclopentadienone XIII is formed by elimination of methanol from a 2-cyclopentenone derivative (XII). The formation of XIII from VII was sensitized by benzophenone and acetophenone, and quenched by piperylene. The mechanisms of these reactions are discussed.