Photo-oxygenation of glycosylfurans. Rearrangement of C-glycosyl into O-glycosyl derivatives

Photo-oxygenation of 3-ethoxycarbonyl-5-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-2-methylfuran and 3-hydroxymethyl-5-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-2-methylfuran yields the corresponding endo-peroxides which rearrange at room temperature into the O-glycosyl derivatives ethyl 2,3-O-isopropylidene-β-d-erythrofuranosyl 2-acetylfumarate and 2,3-O-isopropylidene-β-d-erythrofuranosyl 3-acetyl-3-hydroxymethylacrylate, respectively. The endo-peroxides can be reduced without rearrangement, yielding C-glycosyl derivatives. Alcoholysis of the O-glycosyl derivatives yields 2,3-O-isopropylidene-d-erythrose, dialkyl 2-acetyl-3-alkoxysuccinates, 4-ethoxycarbonyl-5-methoxy-5-methyl-2-oxo-2,5-dihydrofuran and 4-hydroxymethyl-5-methoxy-5-methyl-2-oxo-2,5-dihydrofuran.