A convenient route to higher sugars by two-carbon chain elongation using Wittig/dihydroxylation reactions.
The combination of a Wittig olefination and a dihydroxylation reaction constitutes a facile synthetic protocol for the transformation of unprotected carbohydrates into higher sugars. The Wittig reaction is carried out with tert-butyl or diphenylmethyl ester stabilized phosphoranes to give (E)-configured alpha,beta-unsaturated esters as the only products in most cases. These are dihydroxylated in a diastereoselective fashion using OsO(4)/NMO. The stereochemical outcome in the dihydroxylation follows Kishi's empirical rule and gives high diastereoselectivity (5:1-8:1) when starting from sugars with the 2,3-threo configuration. When starting from sugars with the 2,3-erythro configuration, the diastereoselectivity in the dihydroxylation is low (2:1-2.5:1). As a result, the Wittig/dihydroxylation protocol is most effective for producing higher sugars with the galacto configuration at the reducing end. The two steps can either be carried out individually or, more efficiently, as a one-pot procedure.
Jørgensen
M
M
Department of Organic Chemistry, Technical University of Denmark, DK-2800 Lyngby, Denmark.
Iversen
E H
EH
Madsen
R
R
D002241:Carbohydrates / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry; D006900:Hydroxylation; D008358:Mannose / Q000737:chemistry; D008968:Molecular Conformation; D010429:Pentoses / Q000737:chemistry; D012266:Ribose / Q000737:chemistry; D014994:Xylose / Q000737:chemistry
D002241:Carbohydrates; D010429:Pentoses; C043333:lyxose; D012266:Ribose; D014994:Xylose; D005947:Glucose; D008358:Mannose