Photocatalyzed oxidation of cyclohexene and cyclooctene with (nBu(4)N)(4)W10O32 and (nBu(4)N)(4)W10O32/Fe-III[meso-tetrakis(2,6-dichlorophenyl)-porphyrin] in homogeneous and heterogeneous systems

Photoexcitation of (nBu(4)N)(4)W10O32 is a suitable mean of oxidizing cyclohexene and cyclooctene with O-2 at room temperature and pressure. This process can be carried out in homogeneous solution as well as using the decatungstate in a dispersed form after its heterogenisation on silica. Cyclohexene and cyclooctene are mainly oxidized to the corresponding hydroperoxides as a consequence of primary photoprocesses which lead to the formation of allylic radicals. The presence of the Fe-III[meso-tetrakis (2,6-dichlorophenyl)porphyrin] chloride as cocatalyst strongly affects the photocatalytic properties of (nBu(4)N)(4)W10O32, playing a key role in the allylic-hydroperoxide dependent oxidation of the cycloalkenes. In the photooxidation of cyclohexene, the porphyrin increases the photocatalytic efficiency of the decatungstate in terms of total turnover number and catalyses the decomposition of cyclohexenyl hydroperoxide with the selective formation of cyclohex-2-en-1-ol. On the other hand, its presence during the photoinduced oxidation of cyclooctene favours the formation of cyclooctene epoxide by addition of ROO . and RO . radicals to the double bond. In the case of cyclooctene, the heterogenisation of the decatungstate on the solid support also affects the chemoselectivity of the photocatalytic process in the absence of the iron porphyrin complex.