Higher-carbon sugars. Part 12. The synthesis of new octitols from D-glucose and D-mannose via the osmylation of unsaturated precursors

Abstract

Catalytic osmylation of methyl (E)-2,3,4-tri-O-benzyl-6,7-dideoxy-α-D-gluco-oct-6-enopyranoside (8) produced a mixture of methyl 2,3,4-tri-O-benzyl-β-L-threo-D-gluco-octopyranoside (9) and the corresponding α-D-threo-D-gluco isomer (10) in the ratio ca. 3:1, respectively. After separation from the mixture as the crystalline triacetate (11), the regenerated triol (9) was transformed into L-threo-L-altro-octitol (L-threo-D-gluco-octitol)(12). Methyl (E)-2,3,4-tri-O-benzyl-6,7-dideoxy-α-D-manno-oct-6-enopyranoside (17) furnished a mixture of methyl 2,3,4-tri-O-benzyl-β-L-threo-D-manno-octopyranoside (18) and the corresponding α-D-ihreo-D-manno isomer (19) on catalytic osmylation. The crystalline hexa-acetate (20) derived from the octopyranoside (18) was subsequently transformed into D-erythro-L-altro-octitol (L-threo-D-manno-octitol)(21). Both osmylation reactions proceed in accordance with Kishi's empirical rule. The structural assignments are based on single-crystal X-ray analyses of the acetylated compounds (11) and (20).