1708-93-6Relevant articles and documents
Photoinitiated olefin epoxidation with molecular oxygen, sensitized by free base porphyrins and promoted by hexacarbonylmolybdenum in homogeneous solution
Campestrini, Sandro,Tonellato, Umberto
, p. 3827 - 3832 (2007/10/03)
The photooxidation of various olefins in homogeneous solution under an oxygen atmosphere, by use of visible light, a dye sensitizer, and an oxygen-transfer catalyst, has been investigated. The oxygen transfer from molecular oxygen to olefin involves the following steps: i) photoinduced singlet-oxygen formation, ii) alkyl hydroperoxide formation through the ene reaction, iii) the intermediacy of a reactive molybdenum peroxide, and iv) olefin epoxidation of the remaining substrate or of a second olefin. Among the various sensitizers and catalysts tested, the electron- deficient free base porphyrin 5,10,15,20-tetrakis(2′,6′-dichlorophenyl) -β-octabromoporphyrin and hexacarbonylmolybdenum showed the best performances in terms of robustness and activity. Under suitable conditions, complete olefin conversion may be obtained by adoption of molar ratios of sensitizer/catalyst/substrate of 1:50:2000, with the formation of the corresponding epoxide in up to 38% yield, which corresponds to 77% of the theoretical maximum. Quite interestingly, olefins reluctant to undergo ene reactions may be epoxidized in the presence of a second sacrificial olefin, yielding the corresponding epoxides with up to 80% total selectivity. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
