Minor Products in Photoreactions of α-Diketones with Arenes. Abstraction of Hydroxylic Hydrogen by Triplet Carbonyl

Article abstract of DOI:10.1021/jo00363a020

Photochemical reactions of cyclic saturated α-diketones in toluene or p-xylene produce 1:1 adducts as major products and smaller amounts of reduced diketone and bibenzyls, as expected from previous work.In addition, reaction of BOD gave 2percent of the decarbonylation product, p-methylbenzyl cyclohexyl ketone; reaction of camphorquinone gave a mixture of decarbonylation products (10percent total) including saturated and unsaturated monoketones.These compounds were secondary products arising from reaction of photoexcited diketone with the initially formed adducts; quenching andsensitization studies showed that triplet states of α-diketones were involved in both primary and secondary reactions.The decarbonylation products were also formed by reaction of benzophenone triplets or of tert-butoxy radicals with adducts.Deuterium labeling of the adducts was employed to demonstrate that the decarbonylation process involves abstraction of hydroxylic hydrogen.