Synthesis of L-gulose, L-galactose, and their acetylated aldehydo forms from 6-S-phenyl-6-thio-D-hexoses

Article abstract of DOI:10.1016/0008-6215(90)84069-7

Methyl 6-S-phenyl-6-thio-α-D-glucopyranoside, prepared in high yield from methyl α-D-glucopyranoside by the action of diphenyl sulfide and tributylphosphine in pyridine, was converted into 6-S-phenyl-6-thio-D-glucitol pentaacetate (7) by sequential hydrolysis, borohydride reduction, and acetylation.Oxidation of 7 with 3-chloroperoxybenzoic acid gave the corresponding S-epimeric sulfoxides, which underwent Pummerer rearrangement to 1-epimeric L-gulose S-phenyl monothiohemiacetal hexaacetates.Boron trifluoride-catalyzed reaction of the latter with thiophenol gave theanalogues diphenyl dithioacetal, whereas base-catalyzed methanolysis led to free L-gulose.Treatment of 7 with N-chlorosuccinimide afforded 1-epimeric 1-chloro-1-S-phenyl-1-thio-L-gulitol pentaacetates, which were hydrolyzed to provide aldehydo-L-gulose pentaacetate.The same reaction sequences were performed with 6-S-phenyl-6-thio-D-galactose, synthesized in two steps from 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose, furnishing ultimately L-galactose, its diphenyl dithioacetal pentaacetate, and aldehydo-L-galactose pentaacetate.Similar reaction sequences for the chain-terminal interchange of oxidation state in other ω-S-phenyl-ω-thioaldoses may prove useful for the preparation of less-common sugar derivatives.