Enantiospecific synthesis of shikimic acid from D-mannose: Formation of a chiral cyclohexene by intramolecular olefination of a carbohydrate-derived intermediate

An enantiospecific synthesis of (-)-shikimic acid from D-mannose in an overall yield of 39% is described, in which the key step is an intramolecular Wadsworth-Emmons olefination reaction of a phosphonate. Nucleophilic displacement of triflate from benzyl 2,3-O-isopropylidene-5-O- trifluoromethylsulphonyl-α-D-lyxofuranoside by the sodium salt of t-butyl dimethoxyphosphorylacetate provides a rare example of substitution at the C-5 position of a furanose derivative by a carbanion.