Glycosidation regioselective

Selective 6 -0-silylation is also possible using tin activation, offering an alternative way to 6 -OH derivatives [54]. Thermodynamic isopropylidenation gives, as discussed, the 3 4 -acetal, which then can be transformed into 3 -OH derivatives or 4 -OH derivatives, as described for galactose derivatives above (Scheme 3.30) [55]. Often, the 3, 4 -diol is used directly as an acceptor in 3 -0-regioselective glycosidations. 

SCHEME 4.56 Regioselective glycoside synthesis by anomeric O-alkylation. 

We have reported several examples of regioselective glycosidation of diols 29). In order to facilitate comparisons, we maintained a level playing field by use of -pentenyl donors. Furthermore, manno donors were studied first since. 

Schemes 13 and 14 show the formation of six disaccharides resulting from regioselective glycosidations at the primaiy-OH of acceptor diols. It might...

Based on these results, a novel method for the synthesis of hexose-6-aldehydes from natural carbohydrate sources has been developed by us. Preliminary results for the regioselective oxidation of the primaty alcohol group in glycosides by the dinuclear copper(ll) complex N, A-bis[(2-pyridylmethyl)-l,3-diaminopropan-2-olato] (p-acetato) dicopper(ll) perchlorate (Cu2(bpdpo), (4) are described below. 

Control experiments do not provide evidence for oxidation of the secondary alcohol groups in the glycoside or for degradation of the ligand backbone. A similar regioselectivity was also observed in a benzyl alcohol/1-phenylethanol model system that showed no proof for the oxidation of the secondary alcohol by formation of acetophenone (18, 23,26). 

M. Adinolfi, A. Iadonisi, A. Pezzella, and A. Ravida, Regioselective phenol or carbinol glycosidation of 17p-estradiol and derivatives thereof, Synlett, 12 (2005) 1848-1852. 

Table 5.7 Regioselectivity in intramolecular glycosylations via prearranged glycosides.

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