Photochemistry of Some Extended ?-Systems: Type A and Aryl Rearrangements of Systems with Extended Conjugation Related to Cyclohexadienones and Cyclohexenones. Mechanistic and Exploratory Organic Photochemystry

Article abstract of DOI:10.1021/jo00285a028

6,6-Diphenyl-2(6H)-naphthalenone and 5,6,6-triphenyl-2(6H)-naphthalenone were sinthesized as extended relatives of 4,4-diphenylcyclohexadienone and their photochemistry was investigated.In the case of the diphenylnaphthalenone, irradition resulted in a regioselective phenyl migration and formation of 5,6-diphenyl-2-naphthol whether the photolysis was in methanol or in benzene.Irradiation of the triphenylnaphthalenone in methanol or isopropyl alcohol afforded a product in which one molecule of solvent and one molecule of molecular oxygen were incorporated.Photolysis in acetonitrile led instead to a tricyclic photoproduct in a process reminiscent of the type A rearrangement of 2,5-cyclohexadienones.This tricyclic photoproduct itself was photochemically reactive and rearranged regioselectively to afford 5,7,8-triphenyl-2-naphthol.By trapping, a tricyclic zwitterion was shown to play a role in the rearrangement of the triphenylnaphthalenone.The photochemystry of both naphthalenones was shown by quenching to result from triplet excited states.Lack of reactivity on sensitization suggested the photochemystry derives from T_n.The quantum efficiencies were shown to be lower and the triplet reaction rate slower in the comparison with the monocyclic 4,4-diphenylcyclohexadienone.Finally, enone analogues were investigated.Both 6,6-diphenyl-4,4a,5,6-tetrahydro-2(3H)-naphthalenone and 6,6-diphenyl-4,4a,5,6,10,10a-hexahydro-2(3H)-anthracenone were synthesized.Only the former was reactive; phenyl migration resulted in formation of four stereoisomeric tricyclic ketones whose structures were established by X-ray analysis.For all of the various reactions, mechanisms are provided and discusseed along with MNDO-CI computations.