Higher-carbon sugars. Part 8. The synthesis of some decitols via the epoxidation of unsaturated precursors

Abstract

Sharpless epoxidation of (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-α-D-threo-D-galacto-dec-8-enopyranose (3) with di-isopropyl L-(+)-tartrate as the chiral auxiliary furnished a mixture of 8,9anhydro-1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-galacto-D-galacto-decopyranose (10)(isolated in 63% yield) and the α-D-ido-galacto isomer (11) in the ratio ∼5 : 1. Base-catalysed hydrolysis of the epoxy alcohol (10) gave, via preferential ring-opening of the Payne-rearrangement product (12), 1,2 : 3,4 : 6,7-tri -O-isopropylidene-α-D-altro-D-galacto-decopyranose (8), which yielded Daltro-D-galacto-decitol (13) following acidic hydrolysis and reduction of the resulting decose. The epoxy alcohol (11) was the principal product obtained on Sharpless epoxidation of the decenopyranose (3) with di-isopropyl D-(–)-tartrate as the chiral auxiliary, and was similarly transformed into L-gluco-D-galacto-decitol (L-galacto-D-gulo-decitol)(16). The same strategy was also used in the synthesis of D-gluco-D-galacto-decitol (L-galacto-L-gulo-decitol)(1) and L-altro-D-galacto-decitol (25) from (E)-8,9-dideoxy-1,2 : 3,4 : 6,7-tri-O-isopropylidene-β-L-threo-D-galacto-dec-8-enopyranose (18).