Higher-carbon sugars. Part 2. The synthesis of some decitols via the osmylation of unsaturated precursors

Abstract

Catalytic osmylation of (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-α-D-threo-D-galacto-dec-8-enopyranose (4) produced a mixture of 1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-galacto-D-galacto-decopyranose (8) and the α-D-ido-D-galacto isomer (9) in the ratio ca. 2.5 : 1. Acid hydrolysis of the mixture of triacetals (8) and (9), and reduction of the resulting decoses, permitted the isolation of crystalline L-galacto-D-galacto-decitol (10), which was readily identified by virtue of its C₂-symmetry. By contrast, the corresponding (Z)-isomer (13) exhibited no diastereofacial selectivity on catalytic osmylation, yielding equal proportions of 1,2 : 3,4 : 6,7-tri-O-isopropylidene-α-D-altro-D-galacto-decopyranose (14) and the β-L-gluco-D-galacto isomer (15). Catalytic osmylation of (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-threo-D-galacto-dec-8-enopyranose (23) afforded a 3 : 2 mixture of 1,2 : 3,4 : 6,7-tri-O-isopropylidene-α-D-galacto-D-galacto-decopyranose (24) and the β-L-ido-D-galacto isomer (25). Samples of each of (meso)-galacto-galacto-decitol (26)(C_s-symmetry) and L-galacto-L-ido-decitol (27) were obtained following acid hydrolysis of this mixture and reduction of the resulting decoses.