Bromide glucopyranosyl

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-... 

Cinnolin-3(2//)-one (7) is methylated with diazomethane or methyl sulfate to give 2-methylcinnolin-3(2H)-one. In a similar manner, benzylation with benzyl chloride, cyanoethylation with acrylonitrile in the presence of benzyltrimethylammonium hydroxide and glucosidation with tetra-O-acetyl-a-o-glucopyranosyl bromide in the presence of a base affords the corresponding 2-substituted cinnolin-3(2//)-ones. However, glucosidation of the silver salt of cinnolin-3(2//)-one produces the corresponding O-substituted compound. 

Initially it was necessary to devise an improved method for the preparation of 2-hydroxyglycal esters, because the standard procedure (treatment of an acylglycosyl bromide with diethylamine in benzene or chloroform solution) was inconveniently lengthy in time and frequently afforded only a moderate yield of product (5). As a result of their recent thorough investigation of the kinetic features of the dehydrobromination of tetra-O-acetyl-a-D-glucopyranosyl bromide Lemieux and Lineback... 

Although the Koenigs-Knorr reaction appears to involve a simple backside S 2 displacement of bromide ion by alkoxide ion, the situation is actually more complex. Both a and /3 anomers of tetraacetyl-o-glucopyranosyl bromide give the same /3-glycoside product, implying that they react by a common pathway. 

The carbohydrate 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide reacts with NaCo(CO)4 and PPh3 under 10 atm of CO to yield the expected acetyl (XXIX) and the corresponding alkyl 210). The former decarbonylates readily on storage or chromatography. Retention of configuration at carbon accompanies CO elimination. 

Coupling of 237 with the protected 2-amino-2-deoxy-o -D-glucopyranosyl bromide (348) in dichloromethane in the presence of silver triflate afforded a diastereoisomeric mixture. The isomer related to the natural one was depro-tected with sodium in liquid ammonia, to give the carba-trehalosamine... 

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 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. 

In a synthesis of the L-serine derivative 133, Kunz and Buchholz100 treated N-(benzyloxycarbonyl)-L-serine 2-bromoethyl ester (135) with tetra-O-benzoyl-a-D-glucopyranosyl bromide (136) protection of the... 

Despite the presence of a nonparticipating group at C-2, condensation of3,4,6-tri-0-acetyl-2-(anisylideneamino)-2-deoxy-a-D-glucopyranosyl bromide (159) with 160 in the presence of silver carbonate and sodium sulfate gave N-(benzyloxycarbonyl)-3-0-[3,4,6-tri-0-acetyl-2-(anisyli-deneamino)-2-deoxy-/ -D-glucopyranosyl]-L-threonine methyl ester125 (161). 

Ci4H19Br09 Tetra-O-acetyl-a-D-glucopyranosyl bromide TAGPBR 37 393... 

Compound 33 also lends itself to the synthesis of 1,5-linked disaccharides. Thus, its condensation180 with 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide, and with methyl 2,3,4-tri-O-acetyl-a-D-glucopyranosyluronate bromide, respectively, yields the corresponding /3-D-linked disaccharides (97 and 98). 

Fluorination with Silver Fluoride from Glycosyl Bromide [17] A mixture of 2,3,4,6-tetra- O-acetyl-a-D-glucopyranosyl bromide (5 g) and anhydrous silver fluoride (5 g) in dry acetonitrile (25 ml) was shaken under argon overnight. The resulting solution was filtered and aqueous sodium chloride was added to precipitate any silver ions from the solution. The mixture was filtered and concentrated to a syrup that was... 

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. 

Hirst and Woolvin169 preferentially methylated positions 3, 4 and 6 by the use of glucal, an unsaturated sugar derivative having a 1,2-olefinic bond, introduced by the reduction of triacetyl-a-D-glucopyranosyl bromide with zinc dust and acetic acid. By the action of an ethereal solution of perbenzoic acid on an aqueous solution of 3,4,6-trimethyl-glucal a sirupy product was obtained. This was shown to contain... 

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... 

---