Glucopyranose bromide

When 35 was heated in acetic acid containing hydrogen bromide, the tribromide 46 was obtained as a single product in 74% yield. Debromina-tion of 46 with zinc dust in acetic acid furnished the cyclohexene derivative 47, which was converted into compound 48 by osmium tetraoxide hydroxyl-ation and acetylation. The substitution reaction of 48 with acetate ions provided carba-a-DL-glucopyranose pentaacetate (49), which gave the carba-sugar 50 on hydrolysis. ... 

C,2H22Ou Ca2+ Br2" 7 H20 4-0-/ -D-Galactopyranosyl-D-glucopyranose calcium bromide, heptahydrate (lactose calcium bromide, heptahydrate) LACCCB 31 352... 

The synthesis of a bridgehead sulfonium salt analogue 59, of the naturally occurring glycosidase inhibitor castanospermine, proceeded by a multistep procedure starting from 5-thio-d-glucopyranose pentaacetate <2000JA10769>. The desired bicyclic sulfonium salt 57 could not be obtained from the key bromide precursor... 

As generally expressed in Section I, derivatives of a-D-glucopyranose are thermodynamically more stable than the /3-d anomers, whereas, for the D-glucofuranoses, the opposite stability of the anomers is observed. This regularity also applies to the respective glycosyl bromides and chlorides. 

Apparently, the first use of this reaction in the sugar series was in the preparation33 of tetra-0-acetyl-l-0-tosyl- a -D-glucopyranose (probably the /3-derivative actually, by Walden inversion at carbon atom 1) by the action of silver p-toluenesulfonate on tetra-O-acetyl-a-D-glucopyranosyl bromide in boiling, dry diethyl ether ... 

The reaction can be followed by TLC using 0.25-inn silica gel 60 F-254 plates (E. Merck Company) and ethyl acetate/hexane (1 1) eluent 2,3,4,6-tetra-O-acetyl-oc-D-glucopyranosyl bromide (Rf 0.39) 2,3,4,6-tetra-0-acetyl-1,5-anhydroglucitol (Rf = 0.28) l-deoxy-2, 3, 4, 6-tetra-0-acetyl-l-(2-cyano-ethyl)-8-D-glucopyranose (Rf = 0.20) l-deoxy-2,3,4,6-tetra-0-acetyl-l-(2-cyanoethyl)-a-D-glucopyranose (Rf = 0.16). 

Imidazole or pyridine mediated silylation of l,2-0-[l-exo-ethoxy )ethylidene]-oc-D-glucopyranose failed to give a high yield of the 6-silyl ether due to some polymerization and side reactions. Activation of hydroxyl groups via a tributylstannyl intermediate followed by the tetrabutylammonium bromide catalyzed reaction with tert-butyl-chlorodiphenylsilane was more successful [231], the 6-0-silyl derivative being isolated in 87 % yield.. The lability of this protecting group under benzylation with benzyl bromide and sodium hydride at 0 °C has been observed [449]. 

On the other hand, when 39 was heated with hydrogen bromide in acetic acid, 1,2-di-<9-acetyl-( 1,3/2,6)-3,4-dibromo-6-(bromomethyl)-l,2-cyclohexanediol (50) was obtained, which was converted into 1,2-di-0-acetyl-( 1,3/2)-3(bromomethyl)-5-cyclo-hexene-l,2-diol (51) by debromination with zinc dust in glacial acetic acid [21]. Hydro-xylation of 51 with osmium tetroxide, and successive acetylation yielded 1,2,3,4-tetra-C>-acetyl-6-bromo-6-deoxy-pseudo-a-DL-glucopyranose (52). Nucleophilic substitution reactions of 52 with sodium acetate gave pseudo-a-DL-glucopyranose pentaacetate (55), which gave pseudo-a-DL-glucopyranose (54) by usual hydrolysis [22]. Alternatively, the pentaacetate 55 was obtained as a minor component in a poor yield by nucleophilic substitutions of 2,3,4-tri-0-acetyl-l,6-dibromo-l,6-dideoxy-pseudo-... 

More recently, a facile synthesis of 126 and pseudo-a-L-glucopyranose (137) has been described [32], When the bromolactone 38 was heated with glacial acetic containing hydrogen bromide and subsequently acetylated, DL-(l,3,5/2,4)-2,3-diacetoxy-4,5-dibromocyclohexane-l-carboxylic acid (130) was obtained [31], Resolution of 130 with optically active a-methylbenzylamines provided the enantiomer (131), m.p. 

The preparation of l,6-anhydro-/3-D-glucopyranose in quantitative yield by Karrer and Smirnoff,63 through the treatment of (tetra-O-acetyl-/3-D-glucopyranosyl)trimethylammonium bromide with aqueous alkali at 100°, in all probability proceeded by way of a mechanism analogous to that established by McCloskey and Coleman46 for the preparation start-... 

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