THE PHOTOCHEMISTRY OF 3-NITRO-2-CYCLOHEXENONE

3-Nitro-2-cyclohexenone appears to be unreactive when irradiated with ultra-violet light; no rearrangement of the nitro group to a nitrite e ster or dimerization of the enone to cyclobutane adducts was observed. Cyclobutane containing photoadducts are also not formed when the elec tron poor alkenes, acrylonitrile or methyl acrylate are present. Howev er, cyclobutane adducts are produced with more electron rich alkenes. The cycloadducts from reaction with cyclopentene can be reduced with z inc and acid to give a cyclo-octanedione identical with the product of de Mayo reaction of cyclohexane-1,3-dione with cyclopentene. Photoadd ucts ore also formed with 2-methylpropene; treatment of these with AIB N followed by hydrogenation yields products identical with those produ ced by hydrogenation of the photoadducts formed from ultra-violet ligh t irradiation of 2-cyclohexenone with 2-methylpropene. The presence of the nitro group on the cyclohexenone increases the proportion of the head-to-head regioisomers from 13% of the adduct mixture to 63%. (C) 1 996 Elsevier Science Ltd