Benzyl glycoside

The 5-methyl ether of V-acetylmannosamine cannot be prepared by this route. The D-glucofuranose 42 was obtained from the 5,6-diol by selective benzylation by way of the dibutyltin derivative, followed by conventional methylation. It was converted into the benzyl glycoside 43 with benzyl alcohol under acidic conditions. Conversion into the amine 44 and amide 45 followed the same path as in the pyranose series. Hydrogenolysis gave20 28 (see Scheme 12). 

As a reducing-end building block for coupling with the phosphorylated oxazoline the previously used 3-0-palmitoyl benzyl glycoside appeared suitable if the end product was... 

In general, the anomeric centre is the first position to be protected during a series of protecting group manipulations. The anomeric centre can simply be protected as an alkyl, allyl or benzyl glycoside. These glycosides... 

The conveniently prepared pyruvated benzyl glycosides 12candl2c (Table 2) are first converted by a two-step sequences into the fluoride 47 and the TlPS-deri-vative 48, respectively. The latter are subsequently condensed, using the glyco-desilylation-protocol, to give the desired laminaritjiosides 49 in excellent yield. 

Other substituted-benzyl glycosides that can be selectively removed in the presence of unsubstituted benzyl ethers have been developed. For example, 2-(hydroxycarbonyl)benzyl glycosides are easily sovolyzed by treatment with Tf20 in the presence of di-tert-butylmethyl-pyridine (DBMP). The reaction implies anomeric C-0 bond cleavage since it takes place by lactonization via the mixed anhydride to generate phthalide and the oxocarbenium ion ( Scheme 71) [399]. 

---