Organic photochemistry. Part V. The illumination of some quinones in the presence of conjugated dienes and other olefinic systems

Abstract

When irradiated with light (λ > 400 mµ), chloranil reacted with 2,3-dimethylbutadiene, butadiene, and 2-methylpropene to give bicyclo-octanes, a cyclohexenedione, and a substituted quinone. Under similar conditions, chloranil and diphenylacetylene gave a benzylidenecyclohexadienone; 1,4-naphthaquinone and 2,3-dimethylbutadiene gave a bicyclo-octane, a spiropyran, and a 2 : 1-adduct; and 2,5-dimethylbenzoquinone and 2,3-dimethylbutadiene gave a bicyclo-octane, as a major product.

The fact that dienes attack the oxygen atom of some quinones and the ring-carbon atoms of others is rationalised by reference to the position of the electron-deficient centre in the n,π* and π,π* excited states of the quinones.