O-Isopropylidene derivatives of D-allulose (D-psicose) and D-erythro-hexopyranos-2,3-diulose

Abstract

Oxidation of 1,2: 4,5-di-O-isopropylidene-β-D-fructopyranose (2) with ruthenium tetroxide affords crystalline 1,2: 4,5-di-O-isopropylidene-β-D-erythro-hexopyranos-2,3-diulose (3) in high yield. The latter, on reduction with metal hydrides or on catalytic hydrogenation over platinum, yields 1,2: 4,5-di-O-isopropylidene-β-D-allulopyranose (4) as virtually the sole product. By contrast, sodium amalgam reduction of 3 yields only the D-fructose derivative (2), although in low yield. Also, metal hydride reduction of impure 3, obtained by oxidation of 2 with dimethyl sulfoxide – acetic anhydride, yields equal amounts of both isomers (2 and 4). The stereochemistry of these reductions is complicated by uncertainty as to the conformation of 4 (and possibly of 2), owing to anomalous proton magnetic resonance spectral characteristics observed.Ketone 3, which is unstable in the presence of deuteroxide ion, is smoothly deuterated at C-4 by exchange in hot deuterium oxide – pyridine.Mono-O-isopropylidene derivatives have been prepared by partial acid hydrolysis of 2 and 4.