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.