PHOTOINDUCED, ELECTRON-TRANSFER REACTIONS OF ARYL GLYCOSIDES

Article abstract of DOI:10.1016/0008-6215(84)85240-4

Photoinduced, electron-transfer (e.t.)-sensitized cleavage of phenyl β-D-glucopyranoside in acetonitrile brought about by irradiation at 350 nm, with sensitization with 1,4-dicyanonaphthalene (DCN) in the presence of methanol, proceeds rapidly, to produce 60percent of the theoretical yield of the methyl D-glucosides within 6 h.Incorporation of water, instead of methanol, provides a means of conversion of the aryl D-glucoside into free D-glucose in comparatively high yields.Irradiation of the reaction system at 300-nm wavelength, with sensitization by DCN, produced, despite the higher energy, slightly lower levels of monosaccharide or methyl glycosides than are obtained from sensitized irradiations at 350 nm, concurrent with increased complexity in product composition.At 350-nm irradiation, levoglucosan is as equally favored as D-glucose as the reaction product from the cleavage of phenyl β-D-glucopyranoside in acetonitrile.Solubility of the materials and conformational interconversions are cited as contributing to anomeric and epimeric differences in the product yields reported.Secondary, and competitive, side-reaction products derived from u.v. irradiation in the presence of the sensitizer DCN are attributed to generation, from methanol in the acetonitrile solvent-system, of formic acid, which enhances degradation of the carbohydrates.