Photoinduced electron transfer reactions of chloranil with benzodioxoles

Abstract

Photoinduced reactions of chloranil (CA) with benzodioxoles 3–12 give triaryl orthoformate products 13–22 in 88–98 % yields via a single electron transfer (SET) mechanism. Photo-CIDNP measurements show that ion radical pairs such as (CA˙^–– 3˙⁺) are formed in acetonitrile and neutral semiquinone–benzodioxol-2-yl radical pairs (RP) are formed in benzene as evidenced by the emissive and abnormally enhanced absorptive polarizations of the methylenedioxy protons (–O–CH₂–O–) in the regenerated benzodioxoles in CD₃CN and C₆D₆, respectively. Abnormally enhanced absorptions for the methine proton (2-H) in products 13, 15, 17 and 20 are also observed in C₆D₆ in accord with the formation of a radical pair (RP) intermediate en route to the product.