Sugars bromides

Owing to the reductive reaction conditions, addition products are formed exclusively. However, only sugar bromides such as 47 have been repotted as radical precursors. Both cobalt methods are attractive from an environmental point of view because the need of tin hydride has been excluded. 

To a mixture of sugar bromide (5.84 g) in toluene (100 ml) were added Bu3SnH (12.34 g, 42.4 mmol) and AIBN (0.2 g, 1.2 mmol) under a nitrogen atmosphere. The mixture was heated at 95 °C for 75 min. After the reaction, the mixture was cooled and was poured into petroleum ether. The mixture obtained was filtered and washed with petroleum ether. The solids were recrystallized from ethanol to give 3/-deoxyadenosine in 41% yield [30]. 

To a flask equipped with a cooler were added sugar bromide (0.5 mmol), Ph4Si2H2 (1.2 mmol), ethanol (2.5 ml), and lastly, Et3B (1.2 ml, 1 M THP solution). The mixture was stirred under aerobic conditions. After 4 h, Et3B (1.2 mmol) was added again and stirred for 12 h. After the reaction, the solvent was removed and the residue was chromatographed on silica gel to give the reduction product [36]. 

Ethynylstannanes react with anomeric sugar bromides, and similar alkoxymethyl and alkylthiomethyl halides, to give propargyl ethers (Scheme 60).107... 

Etherification. The reaction of alkyl haUdes with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraaHyl ether is formed on reaction of D-mannitol with aHyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional aHyl bromide, leads to hexaaHyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trim ethyl chi oro s il an e in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

When carbon tetrabromide is used, the alkyl bromide is formed. Providing moisture is excluded from the reaction mixture (HX is formed otherwise), the reaction conditions are completely neutral, affording a convenient preparation of the halides of acid-sensitive substrates (for example, sugars). 

Metal halide salts other than sodium iodide have been used sparsely to prepare halodeoxy sugars from sulfonate esters. Lithium chloride (107) and lithium bromide (33) have found limited application. Potassium fluoride (dihydrate) in absolute methanol has been used (51, 52) to introduce fluorine atoms in terminal positions of various D-glucose derivatives. The reaction is conducted in sealed tube systems and requires... 

The synthesis of halodeoxy sugars has also been achieved by reaction of sugar phosphorodiamido and phosphonamido derivatives with alkyl halides (83). Heating equimolar amounts of 6-(tetraethylphosphoro-diamido)-l,2 3,4-di-0 isopropylidene-D-galactose with methyl iodide (and benzyl bromide) at 140°C. for 4 hours afforded the 6-deoxy-6-iodo (74b) (75%) and 6-bromo-6-deoxy (74c) (56%) derivatives, respectively. 

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-branched sugars or C-oligosaccharides are obtainable through indium-promoted Barbier-type allylations in aqueous media.151 Indium-mediated allylation of a-chlorocarbonyl compounds with various allyl bromides in aqueous media gave the corresponding homoallylic chlorohydrins, which could be transformed into the corresponding epoxides in the presence of a base (Eq. 8.62).152... 

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