Anhydro sugars synthesis

This procedure provided the most important method for the synthesis of anhydro sugars of the hydrofuranol type. 3,6-Anhydro sugars have resulted from the saponification of hexoses esterified at C6 by the following cationogens Br- 3 36 14- 36 CH3 C H4 S020 37, 3S- 39> 40 HO-SCVO-41 42 02N-0-.43 It is very probable that the phosphate ion is also cationogenic and that saponification of a hexose 6-phosphate... 

Scheme 12. Synthesis of terpenoid glucosides via a stereoselective glucosidation of a 1,2-anhydro sugar catalyzed by silica gel.

This section presents selected examples of the use of zeolites and related porous materials for transformations of carbohydrates, that fall beyond the scope of the previous paragraphs. They include the use of zeolites in click chemistry and in a variety of reactions, including the synthesis of anhydro sugars, cyclization, elimination, and addition reactions to the carbonyl group. 

Figure 2.4 Synthesis of glycosyl fluorides from 1,2-anhydro sugars and glycal derivatives.

Scheme 5.69 Synthesis of N-glycosides from 1,2-anhydro sugars.

The same procedure was also applied to the synthesis of a-C-galactosyl compounds. Similarly, reductive ring opening of 1,2-anhydro sugar 93 with titanocene(m) chloride produces an anomeric radical 97 that can be trapped... 

C-6,209,214 anhydro sugars,branched monosaccharides, fluori-nated amino sugars,difluorinated monosaccharides, and fluorinated monosaccharide phosphates,and phosphonates have been described. Further progress has been achieved in the synthesis and n.m.r.-spectral analysis of fluorinated avermectin Bu, tylono-lide, and neuraminic acid derivatives. " ... 

There are several instances where reactive intermediates present during the synthesis of septanosides have reacted intramolecularly to give ring-contracted or bicyclic products.91 Similar intramolecular reactions (such as the formation of 1,6-anhydro sugars) have precedents in the pyranose literature. Such cases of intramolecular reactivity described in the literature notably involve novel ethers or thioethers as the nucleophilic species in the ring contractions. 

Although 2,5-anhydro sugars had, for a long time, been poorly understood, they have now found useful application as intermediates in synthesis, and even as derivatives for the characterization of certain amino sugars. For example, a useful method for the analytical deter-... 

The synthesis of other anhydro sugar derivatives is usually accomplished by an internal displacement of a leaving group with inversion, as has already been emphasized for those anhydrides in which the anhydride bridge engages the anomeric position. Three such compounds that have been used in polymerizations deserve specific mention 5,6-anhydro-l,2-0-isopropylidene-a-D-glucofuranose,12 13 its 3-methyl ether,11 and 3,5-anhydro-l,2-0-isopropylidene-a-D-xylo-furanose,14 all of which were synthesized by p-toluenesulfonylation of the primary hydroxyl group of the parent, isopropylidene derivative, followed by treatment with base. 

---