Sugar 1,2-Orthoesters

Rearrangement of Sugar-Sugar Orthoesters Leading to 1,2-cu-Glycosidic Linkages... 

N. K. Kochetkov and A. F. Bochkov, Sugar orthoesters and their synthetic applications, in R. Bognar, V. Druckner, and S. Szantay (Eds.), Recent Developments in the Chemistry of Natural Carbon Compounds, Vol. 4, Akad. Kiado, Budapest, 1971, pp. 77-192. 

By means of silver salts, alcohols and 2,6-dimethylpyridine sugar orthoesters (405 equation 189) have been prepared from (7-acetylated glycosyl halides. Bicyclic orthoesters (407 equation 190) are accessible by rearrangement of the esters (406). Excess oxalyl chloride reacts with tetrahydrocarb-azole to give the acid chloride (408 equation 191) which is converted by alcohols to orthoesters... 

A. F. Bochkov, V. I. Betaneli, and N. K. Kochetkov, Sugar orthoesters 16. Mechanism of the isomerization of protected a-D-glucopyranose 1,2-orthoacetates by mercuric bromide in nitromethane, Bioorg. Khim.(EngL), 3 (1977) 30-35. 

F. Z. Kong, Recent studies on reaction pathways and applications of sugar orthoesters in synthesis of oligosaccharides, Carbohydr. Res., 342 (2007) 345-373. 

As reported earlier [61], the combination of LiAlH4 and AICI3 [64, 65] was an effective reagent for selective cleavage of the spiro sugar orthoesters. In Table 8.4 the reduced sugar orthoesters and the obtained products are given. 

The reduction of six sugar orthoesters 157, 158, 159, 160, 161, and 162 (Table 8.5) with NaBH3CN proceeded smoothly in the presence of AICI3. The results are summarized in Table 8.5. 

The above results showed that the prepared 12 sugar orthoesters were separated into two groups from the point of reactivity of the reductants and of the... 

In Fig. 8.42 the structures of both sugar lactones and sugar diols used for the synthesis of sugar orthoesters are given. 

For example, the ring systems of the sugar orthoesters 145-148 (Table 8.4) prepared from the sugar lactones 169-172 and 7 75 (Fig. 8.42) had the same structure. 

All of the products in Tables 8.4 and 8.5 resulted from the selective ring opening at the bonds between the anomeric carbons and the axial oxygen atoms. In the cases of the present reductions, it was appropriate to think that the initial step was the elimination of one of the oxygen atoms in the dioxane ring of each sugar orthoester... 

An efficient and stereoselective synthesis of 3,4,6-tri-O-acetyl-ot-D-glucopyranose 1,2-exo-alkyl ortho-acetates (67) has been achieved using DMF dialkyl acetals (68) and tetrabutyl ammonium bromide on acetobromoglucose. The DMF acetal from 1,2 3,4-di-0-isopropylidene bC-D-galactopyranose (69) was also prepared and used to synthesize the mixed sugar orthoester (70). 

The preparation of several glucofuran [2, l-t/] oxazolines 35 and 36 from reaction of 2-amino-2-deoxy-D-glucose 34 with HF has been described. Compounds 35a and 35b are formed when the reaction is carried out in formic acid, whereas the orthoesters 36a-c are formed when the reaction is carried out using anhydrides. Further reaction of 35 and 36 with methanol gives methyl glycosides. Thus, 35 and 36 may hnd use as potential glycosyl donors for the synthesis of 2-amino-2-deoxy sugars (Scheme 8.14). " ... 

A number of anhydro sugar derivatives have been prepared by treatment of orthoesters with mercuric bromide in nitromethane. Among them are 3-0-acetyl-l,5-anhydro-2-0-benzoyl-/3-L-arabinofuranose,68... 

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