Hydroformylation of glycals

Abstract

Hydroformylation of 3,4-di-O-acetyl-d-xylal gave 4,5-di-O-acetyl-2,6-anhydro-3-deoxy-aldehydo-d-lyxo-hexose (I) and 4,5,di-O-acetyl-2,6-anhydro-3-deoxy-aldehydo-d-xylo-hexose (II). Methyl sulfoxide oxidation of 2,3-di-O-acetyl-1,5-anhydro-4-deoxy-d-arabino-hexitol (III) and of 2,3-di-O-acetyl-1,5-anhydro-l-xylo-hexitol (IV) yielded compounds I and II, respectively.Reaction of 3,4,6-tri-O-acetyl-d-glucal with carbon monoxide and hydrogen under carefully controlled conditions yielded 4,5,7-tri-O-acetyl-2,6-anhydro-3-deoxy-aldehydo-d-manno-heptose (VII) and 4,5,7-tri-O-acetyl-2,6-anhydro-3-deoxy-aldehydo-d-gluco-heptose (VIII) in a 70% yield. Compound VII was readily separated from the mixture of aldoses and alditols by column chromatography. Alternatively, aldoses VII and VIII were separated via their 2,4-dinitrophenylhydrazones. The conversion of aldoses VII and VIII into their diethyl dithioacetal derivatives is also described.The formyl group located in an equatorial orientation was found to be reduced at a faster rate than its axial counterpart.