Abstract
TiO2-catalyzed photooxygenation of 1,1-diarylethenes and 1,2-diarylcyclopropanes was investigated. Irradiation of acetonitrile solution of 1,1-bis(p-methoxyphenyl)ethene in the presence of suspended TiO2 and Mg(ClO4)2 under a constant stream of oxygen atmosphere through Pyrex filter with 300 W high-pressure mercury lump afforded 3,3,6,6-tetrakis(p-methoxyphenyl)-1,2-dioxane in 97 % yield. Intramolecular photooxygenation of 1,1,8,8-tetrakis(p-metyhoxyphenyl)-1,7-octadiene gave the corresponding 1,2-dioxane derivatives. Photooxygenation of methoxy-substituted trans-1,2-diarylcyclopropanes afforded a mixture of cis- and trans-3,5-diaryl-1,2-dioxolanes in 4:1 ratio. Prolonged irradiation of acetonitrile solutions of the methoxy-substituted cyclopropanes in the presence of suspended TiO2 and Mg(ClO4)2 caused the photodecomposition of the 1,2-dioxolanes to give methoxy-substituted benzaldehydes and acetophenones. In the absence of Mg(ClO4)2, these photooxygenation occurred quite slowly. When the photoreaction of 1,2-diarylcyclopropanes was carried out in a closed system under a saturated oxygen atmosphere, the oxygenated products were not observed in an appreciable amount, but cis-trans photoisomerization of the cyclopropanes took place to give a photostationary state mixture in cis : trans = 5 : 95 ratio. The photooxygenation and cis-trans photoisomerization proceeds through photoinduced single electron transfer from diarylethenes and cyclopropanes to titanium dioxude.
