Developing an asymmetric, stereodivergent route to selected 6-deoxy-6-fluoro-hexoses

Free radical bromination and nucleophilic fluorination allows the conversion of methyl sorbate into the 6-fluoro analogue which undergoes sequential asymmetric dihydroxylation reactions. A range of 6-deoxy-6-fluorosugars were prepared by using different combinations of ligands. While the enantiomeric excesses obtained were comparable to those from other 6-substituted sorbates, the regioselectivity of dihydroxylation was moderate, with both 2,3- and 4,5-diols being obtained. A successful temporary persilylation strategy was evolved to convert the products of dihydroxylation rapidly to the fluorosugars 6-deoxy-6-fluoro-L-idose, 6-fluoro-L-fucose and 6-deoxy-6-fluoro-D-galactose, which were obtained in overall yields of 4%, 6% and 8% from methyl 6-fluoro-hexa-2E,4E-dienoate .