Synthesis of sedoheptulose from 2-C-(hydroxymethyl)-d-allose by molybdic acid-catalysed carbon-skeleton rearrangement

A new branched-chain aldose, 2-C-(hydroxymethyl)-d-allose (3), was obtained by a base-catalysed addition of 2,3:5,6-di-O-isopropylidene-β-d-allofuranose to formaldehyde followed by acid hydrolysis of the aldol product. On treatment with a catalytic amount of molybdic acid at 90 °C, 3 afforded its equilibrium mixture with sedoheptulose tautomeric and anhydro forms in the ratio 12:1. Sedoheptulose in its 2,7-anhydro form, 2,7-anhydro-β-d-altro-heptulopyranose, was obtained from this mixture by treatment with 0.5 M H2SO4 and crystallisation (overall 63% yield).