Photochemical formation of 1,5-diketones from dibenzoylmethane and some quinones

Irradiation (300 nm UV light) of dibenzoylmethane and 1,4-naphthoquinone in dichloromethane gave 1,5-diketone as the major product, along with beta-hy droxyketone as the minor product. Anthraquinone and anthrone also added pho tochemically to dibenzoylmethane to give 1,5-diketones as the major product s. In contrast, tetrahalo-1,4-benzoquinones added to dibenzoylmethane to gi ve two types of 1,5-diketones via oxetane and cyclobutane intermediates. Co mparison of the potential energy values of the photoproducts reveals that t he 1,5-diketones are more stable than the corresponding oxetanes or cyclobu tanes due to the ring-strain of the bicyclic compounds.