Glycosyl fluorides protected

Glycosyl fluorides may be prepared by displacement of per-O-acyl or suitably protected 2-0-acyl 1-halides (Cl or Br) with fluoride [AgF (Refs. 28 and 29), KHF2 (Ref 30) or AgBF4 (Ref 31)]. -o-Glucopyranosyl [ F]fluo-... 

The preparation of glycosyl fluorides is described next. Aiming to have a convenient glycosyl donor convertible into 1,2-CM-furanosides, Mukaiyama and coworkers prepared 2,3,5-tri-O-benzyl-yS-D-ribofuranosyl fluoride (36y3) by treatment of a protected D-ribofuranose (35) with 2-fluoro-1 -meth-ylpyridinium tosylate (FMPTs) the total yield was raised by anomerizing the simultaneously produced a-1-fluoride (36a, 7, p 66, 72.f 24 Hz) to 36 (7, F 63.5 Hz, 72,F very small ) by treatment with BF3-OEt2. 

Unlike any of the other protected glycosyl halides, glycosyl fluorides can be depro-tected without the loss of the halide function. This makes glycosyl fluorides very rare... 

Glycosyl fluorides, widely used reagents in carbohydrate and natural product chemistry,745 746 can be used to carry out stereoselective synthesis of glycosides with a catalytic amount (5 mol%) of triflic acid. The appropriately protected /3-D-glycosyl fluorides of glucose and galactose as donor molecules, when applied in dichloro-... 

An alternative stereoselective synthesis of chiral heterocycles based on carbohydrate-induced stereodifferentiation includes nucleophilic addition reactions on heterocyclic systems already bound to the carbohydrate auxiliary. An example of this strategy has been shown by stereoselective addition of Grignard reagents to carbohydrate-linked 4-pyridones [61]. For this purpose, trimethylsiloxypyridine was glycosylated regioselectively using pivaloyl-protected glycosyl fluorides. 

Glycosyl fluorides are much more stable and easier to handle than other glycosyl halides. Today they are important building blocks in carbohydrate synthesis. The best method for their preparation is treating either fully or partially protected sugars with the HF-Py complex resulting in 1-fluoro derivatives with an usually predominant a configuration (equation 16)30. 

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