A novel pathway in the photooxygenation of cyclic allenes

The photooxidation of cyclic allenes gives rise to cyclic 1,2,3-trione hydr ates. The formation of these compounds points to a novel photooxidation mec hanism involving both singlet and triplet oxygen, Upon placement of a methy l group on the allene, the mechanism shifts to predominantly an "ene" react ion, The corresponding cycloadditions with 4-methyl-1,3,4-triazoline-3,5-di one (MTAD) with cyclic allenes involve 2 equiv of MTAD, The dipolar interme diates are trapped with H2O to give alpha-urazole-substituted 2-cycloalkeno nes.