2.3.4.6- tetra-O-benzyl- 3-D-glucopyranosyl

Glycosyl fluorides, already addressed as substrates for cyanations and allylations, are excellent substrates for radical-mediated C-glycosidations. As shown in Scheme 7.80, Nicolaou et al. [43] demonstrated such reactions in the coupling of 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl fluoride with acrylonitrile. The reaction gave a 61% yield with an anomeric ratio of greater than 10 1 favoring the a isomer. 

Glycosylation of Methyl 3-0-acetyl-4,6-benzylidene-[Pg.227]

Monti, D., Gramatica, P., Speranza, G., and Manitto, P, A convenient synthesis of both the anomers of ethyl (2,3,4,6-tetra-O-benzyl-D-glucopyranosyl)acetate, Tetrahedron Lett., 28, 5047, 1987. Scremin, C.L., Boal, J.H., Wilk, A., Phillips, L.R., Zhou, L., and Beaucage, S.L., l-(2-Deoxy-a- and P-D-e yf/ rc>-pentofuranosyl)-2-(thyniin-l-yl)ethane derivatives as conformational probes for (z/fDNA ohgonucleotides. Tetrahedron Lett., 36, 8953, 1995. 

Figure 1. Products of the reactions of the diazirine 7 with mono- and dihydroxy compounds solvents, total yields, and P-d/u-d ratios (GlcBn, = 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl).

Allevi, P, Anastasia, M, Ciuffreda, P, Fiecchi, A, Scala, A, The first direct method for C-glucopyranosyl derivatization of 2,3,4,6-tetra-O-benzyl-D-glucopyranose, J. Chem. Soc., Chem. Commun., 1245-1246, 1987. 

Barrett applied this procedure to the synthesis of sucrose (Scheme 5) [7]. 2,3,4,6-Tetra-O-benzyl-D-glucopyranose was converted into the a-glucopyranosyl ester 25 with excellent selectivity. In this case the methylenation using Tebbe reagent was unsuccessful. However, the Nozaki-Takai protocol gave the desired vinyl ether. After desilylation, the cyclization reaction gave only the P-fructofuranosyl derivative 26 when the reaction was performed in the presence of silica. 

Noyori and coworkers found that tetrafluorosilane or trimethylsilyl tri-flate catalyzes the condensation of appropriately protected glycopyranosyl fluorides with trimethylsilyl ethers or alcohols. The strong affinity of silicon for fluorine was considered to be the driving force for this reaction. In the case of Sip4, attack of a nucleophile on the glycosyl cation-SiFj ion-pair intermediate was anticipated. Thus, condensation of 2,3,4,6-tetra-O-benzyl-a- and - -D-glucopyranosyl fluorides (47a and 47fi) with methyl... 

A route to a-glycosides involves treatment of a 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl bromide with an alcohol, tetraethylammonium bromide, and diisopropylethylamine in CH2C12. Explain the stereoselectivity of this reaction. 

Tetra-O-benzyl-a-D-glucopyranosyl Fluoride Typical Procedure 301... 

G. Glycosylation of 3-methoxy-2-pyridyl 2,3.4-tri-O-benzoyl-P-D-glucopyranoside with 2,3,4.6-tetra-O-benzyl-p-D-glucopyranosyl 2-thiopyridylcarbonate 459... 

Glycosidation. The silver imidazolate-HgCl2 system favors formation of a-glucosides from reaction of 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl chlorides and -a-D-gallactopyranosyl chlorides with sterically hindered alcohols. Addition of tetra-u-bulylammonium chloride (1.4 equiv.) enhances the rate.1... 

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