Penta-acetyl glucose

The n-octylaminocarbene complex derived from glucose is synthesized from penta-acetylated gluconic acid chloride 326 addition of potassium pentacarbonyl chromate 251 followed by methylation gives chromium methoxycarbene 327 that undergoes low-temperature aminolysis with u-octylamine and 0-deprotection under basic conditions to afford chromium n-octylaminocarbene 328 (Scheme 11.68) [127]. 

Acetates. Complete acetylation of all the hydroxyl groups is desirable in order to avoid mixtures. In some cases, the completely acetylated sugars may be obtained in the a- and p-forms depending upon the catalyst, e.g., zinc chloride or sodium acetate, that is employed in the acetylation. The experimental details for acetylation may be easily adapted from those already given for a- and p-glucose penta-acetates (Section 111,137). 

Penta-O-acetyl-a/de/iycfo-D-glucose 2,4-Di-0-acetyl-6-0-trityl-D-glucopyranose or a/dehydo-D-glucose pentaacetate... 

The similarity of the products obtained by ammonolysis, either of acylated nitriles, or of acylated aldehydo monosaccharides having one carbon atom less than the corresponding nitriles, was verified12 by ammonolysis of 2,3,4,5,6-penta-O-acetyl-aWehydo-D-glucose (20), which afforded the same N-acetyl-a-D-glucofuranosylamine (15) as that obtained from the peracetylated heptononitrile 14. 

There have been few investigations of the reactions of polyhydroxy compounds with alkali metal alkoxides in nonaqueous media at room temperature.. Percival" reported the preparation of D-glucose-NaOEt and D-glucose NaOMe by treating d-glucose with sodium ethoxide, and penta-O-acetyl-D-glucopyranose with sodium methoxide, respectively. The adducts were dried under vacuum at 60° for 24 hours, a treatment which would make the presence of any significant proportion of alcohol of solvation unlikely. Any traces of moisture in the preparative medium preclude the formation of an aJkoxide adduct. 

An entirely different approach to pyranoid 4-enes depends on eliminations from 5-bromo compounds obtained from pyranoid hexuronic acid derivatives by photobromination. Treated with zinc-acetic acid, the bromide 249 gives the glycal -like 250 (62%), while the 4-acetoxy compound 251 is formed when DBU is used to promote elimination. Similarly, base treatment of penta-0-acetyl-5-bromo-/J-D-glucose with DBU causes the analogous loss of hydrogen bromide and formation of the 4-acetoxy-4-ene, but use of zinc-acetic acid affords mainly the 5-exo-methylene alkene by the alternative available elimination process.237... 

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