Irradiation of 1,3-cyclohexanedione and p-benzoquinone in methanol gave 3-methoxycyclohex-2-en-1-one. Allyl derivative of the 1,3-diketone was prepared as enol from and irradiated in methanol in the presence of p-benzoquinone to give the same type of photoproduct, i.e., 2-allyl-3-methoxycyclohex-2-en-1-one. Allyldibenzoylmethane was synthesized and irradiated with p-benzoauinone in methanol but no remarkable amount of photoproduct was obtained.