Photochemical Preparation of Ozonides by Electron-Transfer Photo-Oxygenation of Epoxides

摘要

9, 10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemist of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis-and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trixolane. The same stereochemical course is followed for the electron-transer photo-oxygenation of more easily oxidized 2,3- dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3, 5-bis (2'naphthyl)-1,2,4-trioxolane. The corresponding transchemically identified by chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase.