Carbonate protection, mannosides

Figure 6.32 Successes and failure of carbonate protection in an attempt to make aryl P-mannobiosides. The formation of the cyclic orthocarbonate must be entirely due to the complex phosphine oxide leaving group in the Mitsunobu reaction, since 4,6-di-O-acetyl-a-D-mannopyranosyl bromide 2,3-carbonate gave the expected aryl P-mannosides on reaction -with phenoxides. ...

Classically, one of the more successful systems for p-mannoside generation was based on the activation of a 2,3-0-carbonate protected mannopyranosyl halide by... 

Silver cations on the surface of insoluble catalysts anchor mannosyl bromides from the a-side [52]. As a consequence, highly reactive alcohols can attack the anomeric center from the P-side in an Sn2 type reaction, thus leading to P-mannosidic linkages. The first application of this principle was reported by Perlin [53] in 1961 who condensed the cyclic carbonate-protected mannosyl bromide [54] 2 and the reactive aglycone 3 under silver oxide activation to afford the first synthetic disaccharide (4) that contains a P-mannopyranosidic linkage (Scheme 2). 

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