Synthesis of octoses by brimacombe methodology; a hard proof for the structure of the anti-kishi product of osmylation of unsaturated ester

Reaction of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranos-6-ulose with Ph 3 P=CH-CO 2 Me conducted in methanol afforded exclusively the Z-α,β-unsaturated ester, which was further reduced with DIBAL-H to the allylic alcohol. Osmylation of the unsaturated ester afforded two stereoisomeric diols in a 4:1 ratio, with the 'anti Kishi product' predominating, while the same process performed on the allylic alcohol provided the expected 'Kishi product' with high selectivity. The structure of the latter was confirmed by X-ray analysis of its 8-O-tritylated derivative.