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Trifluoroethanol was converted into difluorinated (racemic) analogues of amicetose and rhodinose by metallated difluoroenol acetal chemistry, protection, release of the latent difluoromethyl ketone, stereoselective reduction and ozonolysis in acidic methanol. A fortuitous separation of diastereoisomers allowed the diastereoisomeric pyranoses to be obtained cleanly. Though reductive defluorination allowed a facile entry to the route, the corresponding monofluoro sugar analogues could not be separated. Instead, Sharpless asymmetric epoxidation followed by epoxide ring-opening with an unusual nucleophilic fluoride source allowed enantiomerically highly enriched and selectively protected fluorodiols to be obtained. Ozonolysis then afforded the methyl pyranosides, which could be transformed in a number of ways.
- synthetic methods