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

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Abstract
Oxidation of 1,2:4,5-di-O-isopropylidene-([beta]-D-fructopyranose (2) with ruthenium tetroxide affords crystalline l,2:4,5-di-O-isopropylidene-[beta]-D-erythro-hexopyranos-2,3-diulose (3) in high yield. The latter on reduction with metal hydrides or on catalytic hydrogenation over P, yields 1.2:4,5-di-O-isopropyli-dene-[beta]-D-allulopyranose (4) as virtually the sole product. By contrast, Na 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 were prepared by partial acid hydrolysis of 2 and 4.

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