For glycoside formation

The LevS group is stable to the conditions used for glycoside formation... 

The mechanism of iV-glycoside formation is analogous to the mechanism for glycoside formation, and both anomers of the A -glycoside are formed as products. 

The protection of alcohols with allyl [71] and related (prenyl, methylallyl, cinnamyl, homoal-lyl) groups is of great importance in carbohydrate synthesis due to their stability under the conditions required for glycoside formation. These groups are moderately stable to acids and bases, and offer the potential for selective dealkylation of differentially protected sites. 

O Scheme 21) [80,81,82]. Bilberg and Lonn also found the significance of solvent for glycoside formation the use of a mixture of MeCN-CH2Cl2 (3/2) afforded the best result. The optimized activation system extended the usage of 2-xanthate derivative 63 to the assembly of a variety of sialyl oligosaccharides as shown in Fig. 8 [83,84]. 

The use of allyl ethers for the protection of alcohols is common in the carbohydrate literature because allyl ethers are generally compatible with the various methods for glycoside formation. Obviously the allyl ether is not compatible... 

Scheme 2. The glycosyl fluoride method for glycoside formation (a) and its application (b) to the synthesis of a-cyclodextrin (6). (Ogawa, 1987) ...

Synthesis of Monosaccharide Glycosides.- A very useful review has appeared on newer methods for glycoside formation, particularly those based on 0-alkylation and on the use of glycosyl trichloro-acetimidates, sulphonium salts and fluorides. A shorter paper has... 

In recent years Knoechel and coworkersreported on the Koenigs--Knorr reaction and studied the influence of a macrocycle on the reaction. This reaction is important because of its synthetic utility for glycoside formation. The authors showed that the macrocycle promotes a fast reaction with better yield and that the product distribution is sensitive to the nature of the macrocycle and to the bulkiness of the alcohol. 

Figure 39 illustrates that the aldehyde group at C-1 and the hydroxyl group at C-5 come rather close together. This proximity facilitates the reaction leading to hemiacetal formation. Aldehydes in general can add hydroxyl compounds to the C=0 bond (cf. Chapt. 1-2). If H—0—H is added, the product is the hydrate of the aldehyde if an alcohol is added the hemiacetal is formed. Full acetals (or simply acetals ) arise from hemiacetals plus alcohols by elimination of water. This reaction is the basis for glycoside formation by carbohydrates (see formulas below). 

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