The Photochemistry of some Substituted 2-Cyclohexenones and the Excited States Involved

Abstract

<p> The photoadditions of 3-phenyl-2-cyclohexenone to bicyclo [2.2.1] hepta- 2,5-diene, bicyclo [2.2.1] hept-2-ene and cyclopentene have been studied. In all cases cis fused cyclobutane products were obtained. Quenching and sensitization experiments indicated a singlet excited state to be active in photocycloaddition. Phosphorescence and fluorescence emission were observed from 3-phenyl-2-cyclohexenoneo Energy transfer to the lowest triplet of 3-phenyl-2-cyclohexenone was evident from the quenching of Michler's ketone phosphorescence. Two norbornene dimers were detected in the photolysis of 3-phenyl-2-cyclohexenone and norbornene giving evidence for a higher triplet excited state of the enone. The photoaddition of 3-methyl-2-cyclohexenone to cyclopentene was studied for comparison and both cis and trans fused adducts were obtained. In photolyses with bicyclo [2.2.1] hepta-2,5-diene or cyclopentene, 2-phenyl-2-cyclohexenone was unreactive. </p>