Glucopyranosyl bromide reaction with

The synthesis93 of N-(2,4-dinitrophenyl)-3-0-(tetra-0-acetyl-/ -D-glu-copyranosyl)-L-threonine methyl ester (131) involved a two-step procedure. First, formation of the intermediate, L-threonine orthoester 130 was achieved by treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (128) with the methyl ester of N-(2,4-dinitrophenyl)-L-threonine94 (129) under the conditions of the Koenigs-Knorr reaction (see next paragraph), and this was then converted into the L-threonine glycoside 131. 

Schultheiss-Reimann and Kunz(43) applied silver triflate as the promoting reagent for the reaction of 2,3,4-tri-O-benzyl-a-D-glucopyranosyl bromide (52) with V-(9-fluorenylmethoxycarbonyl)-L-serine benzyl ester to... 

For the 2-phenyloxazolines, the reaction is performed, for example, by treating tri-0-acetyl-2-benzamido-2-deoxy-a-D-glucopyranosyl bromide (134) with hydrobromic acid158- 184 to give 135. Alternatively, the unacetylated 2-acylamido-2-deoxy-D-glucose is treated with hydrochloric acid in acetone, and the 5,6-isopropylidene acetal (136) is obtained.165 Compound 136 has proved a valuable intermediate in the synthesis of several amino sugars.186- 172... 

In accord with the reactions undergone by, for example, tetra-0-acetyl-a-D-glucopyranosyl bromide (23) with bases, and with zinc - acetic acid, which give tetra-0-acetyl-1,5-anhydro-D-arabino-hex-1 -enitol ( tetra-0-acetyl-2-hydroxy-D-glucal ) (158) and tri-O-acetyl-1,5-anhydro-2-deoxy-D-ara >/ o-hex-I-enitol ( tri-O-acetyl-D-glucal ) (159), respectively (see Scheme 24),... 

To explore the dependence of the equilibrium on the nature of the anion, the fluoroborate salt of 59 was prepared. It was obtained at low temperature (0 ) either by the reaction of tetra-0-acetyl-/3-D-glu-copyranosyl fluoride (53) with boron trifluoride in carbon tetrachloride, or by treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (54) with silver fluoroborate in nitromethane. In edier, compound 54 and silver fluoroborate give a mixture of tetra-O-acetyl-a- and /3-D-glucopyranosyl fluoride, because the ether complexes with the boron trifluoride, and so a fluoroborate anion is no longer available. On dissolution of the fluoroborate salt of the D-gluco acetoxonium ion (59) in nitromethane or acetonitrile, an acyloxonium-ion rearrangement, is observed with consequent equilibration, between 59 60 61 62, that is not significantly different from... 

Reaction of 2,3,4,6-tetra-(9-acetyl-a-D-glucopyranosyl bromide (55) with tribu-tyltin hydride and acrylonitrile under photolytic conditions afforded the a-glycoside (56) in 75% yield with an a/p ratio of 93 7 (Scheme 11.14). 

Condensation of the appropriate per-O-acetylated glycopyranosyl bromide with 4-aminobenzenethiol in the presence of sodium methoxide has been used to prepare 4-aminophenyl l-thio-j3-D-gluco-, -galacto-, and -xylo-pyranosides and 4-aminophenyl 2-acetamido-2-deoxy-1 -thio-jS-D-glucopyranoside. 4-Amino-phenyl l-thio-/3-D-glucopyranosiduronic acid was synthesized by condensation of methyl (2,3,4-tri-O-acetyI-a-D-glucopyranosyl bromide)uronate with 4-aminobenzenethiol, followed by saponification with sodium hydroxide. An attempt to obtain the l,2-ci5-l-thioaldopyranoside by reaction of 4,6-di-0-acetyl-2,3-0-carbonyl-a-D-mannopyranosyl bromide (191) with sodium 4-nitrobenzene-... 

Under conditions, the reaction of tetra-o-acetyl-o-glucopyranosyl bromide with A-4-thiazoline-2-thione provides the glycosylamine (76) (N-alkylation) (Scheme 36) (163). However, treatment of 5-... 

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. 

The glycals are easily converted into the 1,2-dihalo-derivatives, which in principle can act as glycosyl donors. However, these derivatives have not found wide application in glycoside synthesis, mainly because of the low facial selectivity in the initial addition of the electrophilic species [143-145]. In an example of a successful application, 2-deoxy-2-bromo-a-D-glucopyranosyl bromide [146] has been shown to give predominantly the 2-deoxy-P-D-glucopyranosides in silver-triflate-promoted reactions with alcohols. 

FIGURE 7.14 Activated esters for temporary protection and activation of Fmoc-amino acids for the synthesis of glycopeptides. (A) Reaction of a-D-glucopyranosyl bromide with esterified Fmoc-serine. (B) Reaction of 2-acetamido-2-deoxy-3,4,6-triacetyl- 3-D-glucopyranosyl amine with esterified Fmoc-aspartyl chloride.37-38 Pfp = pentafluorophenyl. 

The reaction of protected a,D-glucopyranosyl bromides with sodium arene tellurolates gives rise to the corresponding telluro / -D-glucopyranosides. ... 

Thus, when the silver salt of 2-quinoxalinone is condensed with tetra-O-acetyl-cr-D-glucopyranosyl bromide in xylene, the 2-glucosyl-quinoxaline (233 R = H R = Ac) is isolated. The latter compound is readily deacetylated to the glucoside (233 R = R = H). During the reaction only the 2-O-substituted derivative is formed (steric factors probably inhibit /V-glucosidation), and only the / -D-anomers are obtained.234... 

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