Furanoside fluoro

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. 

H- and F-N.m.r. Data for 3-Deoxy-3>fluoro-D-pento-fiiranoses and -furanosides... 

Another interesting use of the imidazylate gr up in the furanoside series has been described by Tann et al. [89]. Thus, treatment of the C-2 imidazylate ester of the a-D-ribofuranoside tribenzoate derivative with KHF2 and HF, at 160°C, led to the 2-deoxy-2-fluoro sugar in 63% yield, presumably through the intermediacy of the fluorosulfate ester (HPLC). The 2-fluoro compound is a key intermediate in the preparation of 2 -fluoro-2 -deoxy D-arabinofuranosyl pyrimidine nucleosides, which exhibit powerful antiherpetic activity [89] (Scheme 12). 

As with acetoxy furanosides, reactions with trimethylsilyl cyanide have also been applied to fluoro furanosides. These reactions, illustrated in Scheme 2.2.10,5 unlike those mentioned above, produced high yields of 1 1 anomeric ratios even when run at -78°C. 

Treatment of the D-arabino- and D-xylo-furanosides 1 and 2 with DAST afforded the deoxyfluoro derivatives 3 and 4 in the former case, whereas the latter gave the anhydro-sugar 5 and the deoxyfluoro compound 6 (Scheme 1). Osmium tetroxide-catalysed dihydroxylation of the chiral unsaturated derivative 7 led to the synthesis of 2-deoxy-2-fluoro-D-xylose and -L-lyxose." 1,2,5-Tri-deoxy-2-fluoro-1,5-imino-D-glucitol and 1,2,5-trideoxy-1 -fluoro-2,5-imino-D-... 

Benzyl 3-deoxy-3-fluoro-p-D-glucopyranoside, D-89 Benzyl 5-deoxy-3-C-(hydroxymethyl)-a-L-lyxofuranoside, D-230 Benzyl 3-deoxy-3-iodo-p-L-xylopyranoside, D-280 Benzyl l-deoxy-4,5-0-isopropylidene-D-erji/irO hexo-2,3-diulo-3,6-furanoside, D-186... 

A number of 2,6-dideoxy-6,6,6-trifluorohexoses were prepared from a six-carbon acetylenic precursor via selective hydroxylation of the derived alkene diastereomers, and differences in stereoselectivity of reduction of a trifluoro-methyl ketone compared with the corresponding methyl ketone are outlined in Chapter 18. Oxidation of methyl 5-0-benzyl-3(2)-deoxy-3(2)-fluoro-a-D-pento-furanosides (DMSO/TFAA) was accompanied by epimerization at the fluori-nated carbon atom a- to the ketone resulting in formation of the corresponding 2-(or 3-) keto derivatives as mixtures of two epimers. Reduction then afforded various mixtures of 2- and 3- fluoro compounds. ... 

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