6-bromo-6-deoxy

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. 

Several other methods for the introduction of halo atoms at C-6 in hexose derivatives have been known since the late 1920s. One of the earlier methods involved the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-glucopyranoside with phosphorus pentachloride which resulted only in an 8% overall yield of methyl 6-chloro-6-deoxy-a-D-glucoside (57). In contrast, the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-altropyranoside with phosphorus tribromide and bromine afforded a 73% yield of the corresponding 6-bromo-6-deoxy derivative (91). 

C17H23Br09 Methyl 2,3-anhydro-6-bromo-6-deoxy-4-0-(4,6-di-0-ace-tyl-2,3-dideoxy-a-D-erythro-hex-2-enopyranosyl)-a-D-allopyranoside (MBEHAP)98... 

C7H13BrOs Methyl 6-bromo-6-deoxy-a-D-galactopyranoside MGALBH 31 366... 

For reaction of methyl 6-bromo-6-deoxy-a-D-glucopyranoside with benzoylimidazole the yield of the 2,3-dibenzoyl product is 75% further benzoylation at C-4 occurs only to the extent of 15% tl89]... 

T ri-0-acetyl-4-bromo-4-deoxy-a-D-gaJactopyranoside, tri-0-acetyl-6-bromo-6-deoxy-j8-D-fructofuranosyl 53-55 +40.8 (C) lH n.m.r. 124... 

Dibromo-4,6-dideoxy- di-0-(methylsulfonyl)-a- D-galactopyranoside, 6-bromo-6-deoxy-tri-0- (methyIsuIfonyI)-/3-D- fructofuranosyl 140-141 +54.8 (A) H n.m.r. 97... 

Since tosyl group and bromide have the same efficiency as leaving groups, the synthesis in good yield of heptakis-6-thioglycosyl- cyclodextrin (17 e, 17f) from the heptakis(6-bromo-6-deoxy)- cyclodextrin (15c) needs, as expected, the sodium salts of 1-thiogalactose (16c, 16d) and high temperature (Scheme 6) [27]. 

Methyl 6-amino-6-deoxy-a-D-glucopyranoside derivatives 2c were synthesized in our laboratory by a somewhat different procedure [31]. 6-0-Sulfonyl or 6-bromo-6-deoxy derivatives of methyl a-o-glucopyranoside were substituted at C-6 by sodium azide. The 6-azido-6-deoxy intermediate was then treated by acyl chlorides in the presence of triphenylphosphine (Staudinger reaction) to afford amido derivatives which were finally de-O-acetylated to give 2c. The same reaction pathway allowed the preparation of 6-alkylamido-6-deoxy-D-glucopy-ranose derivatives, starting from o-glucose [31]. 

Neighboring-group participation reactions by sulfur and nitrogen functions have also been observed for deoxyhalogeno sugars. An example is the formation of the anhydride 146, which possesses an oxathiabicyclo[2.2.2]octane ring-system constrained in a boat-like conformation, on treatment of methyl 4-0-benzoyl-2-S-benzoyl-6-bromo-6-deoxy-2-thio-Q -D-altropyranoside (145) with methanolic... 

Melton and Slessor207 have prepared mono-6-chloro-6-deoxy-, mono-6-bromo-6-deoxy-, and mono-6-deoxy-6-iodo-cyclohexaamylose by nucleophilic displacements of the sulfonate group in mono-6-O-p-tolylsulfonylcyclohexaamylose. The monoiodo and monochloro derivatives were each reduced to mono-6-deoxycyclohexaamylose over W-2 and W-4 Raney nickel catalysts, respectively. 

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