Oxirane oxidation with alkaline hydrogen peroxide

The most convenient route to fluorinated epoxides is the direct epoxidation of alkenes. Since first reports of a general method using alkaline hydrogen peroxide at low temperature/ 88" " 9I several alternative synthetic approaches have been developed. Molecular oxygen under free-radical conditions has been used to oxidize alkenes such as tetrafluoroethene or hexafluoro-propene 592 394 however, internal epoxides are formed most conveniently using hypochlorites.595 399 The products, e. g. oxirane 14 from alkene 13, are usually obtained in high yield with retention of configuration.59 ... 

Few publications deal with the oxidation of the oxiranes. This method is used for synthetic purposes if it is difficult to prepare the desired compound by other means. Alkaline hydrogen peroxide induces splitting of a C-C bond in most terminal oxiranes. The result of the reaction is a disubstituted ketone via a 3-hydroperoxyalcohol (Eq. 153) monosubstituted oxiranes yield glycols. 

The conversion of 3-chloropentafluoropropene to 2-(chlorodifluoromethyI)-2,3,3-trifluoro-oxirane (33) can be carried out64 by heating the mixture of the alkene and oxygen in 1,1,2-trichlorotrifluoroethane (CFC-113) in an autoclave.64 The oxidation with hydrogen peroxide in alkaline solution is negatively influenced by the high nucleophilic reactivity of allylic chlorine.65 66 The reaction is performed at very low temperatures that favor the attack of the hydroperoxy anion in competition with the hydroxy anion. Acceptable yields of 31 -38 % are obtained in the presence of a phase-transfer catalyst.66... 

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