Photo-bromination of carbohydrate derivatives. Part 2. Penta-O-acetyl-β-D-glucopyranose; the 5-bromo-derivative and products of further bromination

Abstract

Photo -bromination of penta-~-acetyl-P-D-glucopyranose with N-bromosuccinimide in carbon tetrachloride causes specific replacement of H-5, and the 5-bromo-derivative can be isolated crystalline in high yield. By-products of the reaction contain monobromoacetyl and dibromoacetyl groups. When bromine was used as reagent the 5substituted compound was again formed as initial product, but, ultimately, tetra-o-acetyl-a-D-giucopyranosyl bromide and dibromides with halogen substituents at C-1 and C-5, and with both bromine atoms at C-1, were also produced. A two-step route from glucose penta-acetate to 1,2,3,4-tetra-O-acetyI-6-deoxy-~-D-xy/o-hex-5-enose is defined. Since the C-5 epimer of the penta-acetate affords the same products, it is proposed that the initial bromination proceeds by way of a discrete radical at the tertiary site.

Conformational effects in 2‐deoxyglucopyranos‐1‐yl radicals

“…CI Isomer 3a: ' 24 H 5.39 Found C 50. 24 H 5.33 3) Synthesis of Phenyl 3,4,6-Tri-O-acetyl-2-deoxy-l-seleno[5-2H]-~-~-arabino-hexopyranoside (4): Because the synthesis of the deuterated pyranoside 4 from the 5-bromoglucopyranoside 11 26) follows known procedurcs of undeuterated sugars, the intermediate compounds 12-14 were used without further characterization or purification for the next synthetic steps. a) 1,2,3,4,6-Penta-0-acetyl[5-2HJ-~-~-glucopyranose (12): 1,2,3,4,6-Penta-0-acetyl-5-bromo-~-~-glucopyranose~~~ (11) (4.0 g, 8.5 mmol) was dissolved in tetrahydrofuran (50 ml) under argon in a 100-ml three-necked flask equiped with a septum and a reflux condenser.…”

Non-Stick Sugars: Synthesis of Difluorosugar Fluorides as Potential Glycosidase Inactivators

“…The presence of the 1,1-gem difluoro moiety resulted in a dramatic decrease in the rate of radical bromination relative to that of a β-configured anomeric fluoride or chloride. Complete consumption of starting material required 48 h, which is considerably longer than most of the previously reported photobromination reactions on sugar rings, which are typically complete within 5 h. [26,31,32,34] The formation of the desired 5-bromide 9 was accompanied by the formation of multiple, uncharacterized, side products that presumably arise from the bromination of the acetate methyl groups. [32] Compound 9 was found to be considerably less reactive than the other 5-bromo species prepared.…”

“…[23,24] Two methods have been reported for the installation of a 5-fluoro moiety, both of which rely on the nucleophilic attack of a fluoride ion. The C5 carbon is activated towards nucleophilic attack either as the C5-bromide (which is installed through a light-catalyzed radical bromination reaction) [18,[25][26][27][28][29][30][31][32] or as a C5-C6 epoxide. [33] The installation of fluorine at C5 has most often been accomplished through the radical photobromination route, via the C5 bromide, although this method suffers from the drawback of only tolerating a limited number of aglycones at the anomeric centre.…”

X-ray and theoretical analysis of the relationship between substituent steric effects and the structure of bicyclo[1.1.0]butane. The unexpected flexibility of the bicyclo[1.1.0]butane skeleton

“…In terms of useful structural data, our preliminary reports7,9 and the reports of Irngartinger10 and of Schaefer and Trotter* 11 represent the major X-ray studies of derivatives of bicyclo-[1.1.0]butane.12 The investigations of Irngartinger10 and Trotter11 involved bridged derivatives of bicyclo[ 1.1.0] butane, in which the structure of the bicyclo [1.1.0] butane moiety of these tricyclic molecules was governed in large part by the nature of the carbon chains that joined the endo-2 and endo-4 positions of the bicyclo [1.1.0] butane moiety. Thus, the influence of substituents on structure could best be assessed in nonbridged systems such as 1-3.…”