Synthesis of L-gulose, L-galactose, and their acetylated aldehydo forms from 6-S-phenyl-6-thio-D-hexoses.
Methyl 6-S-phenyl-6-thio-a-D-glucopyranoside, prepared in high yield from methyl a-D-glucopyranoside by the action of diphenyl disulfide 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 the analogous 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-a-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 omega-S-phenyl-omega-thioaldoses may prove useful for the preparation of less-common sugar derivatives.
Santoyo González
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Department of Chemistry, University of Ottawa, Ontario, Canada.
Baer
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D000107:Acetylation; D000447:Aldehydes / Q000138:chemical synthesis; D055598:Chemical Phenomena; D002621:Chemistry; D005690:Galactose / Q000138:chemical synthesis*; D005947:Glucose / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D008722:Methods; D015394:Molecular Structure
D000447:Aldehydes; D005947:Glucose; D005690:Galactose