Locked anomeric configuration method

V. K. Srivastava and C. Schuerch have first introduced 1,2-O-dibutylstannylene acetal-mediated methyl and allyl P-glycosylation for mannopyranose in 1979 [20]. This has recently been successfully developed by G. Hodosi and P. Kovac as a titled concept Scheme 2 shows the general procedure used. Synthetically difficult, 2-cis P-glycosides, especially P-mannopyranosides, can be obtained by this method. The possibihties and problems of the locked anomeric configuration method are discussed in this section. 

Locked Anomeric Configuration Method for Rhamnosyl Stannylene Acetal... 

Locked anomeric configuration method results in complete p-selectivity in oligosaccharide synthesis [25, 26]. The electrophile must be converted to an active tri-flate and inactive bromide, iodide and mesylate cannot be used. Addition of CsF or BU4NF into the reaction effectively increases the solubility of the staimylene acetals. Accompanying formation of the formate derived from the primary Inflate at room temperature can be suppressed by reducing the reaction temperature to —5°C. Table 1 shows results from coupling the 1,2-O-stannylene acetal of rhamnose (54) with primary and secondary triflates (57 and 58) in the presence of CsF. 

Locked Anomeric Configuration Method for Mannosyl Stannylene Acetal Isomerization of Acetal [25, 26]... 

The advantages of the anomeric 0-alkylation and glycosylation via locked anomeric configuration methods are ... 

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