Glycopyranoside

According to van deer Veen (27) and Rao and Foster (17 the anomeric proton line positions for a-D-glycopyranosides (H equatorial) appear in the region of 4.8 to 5.5 p.p.m., while for / -D-glycopyranosides (Hi axial), the peaks appear at 4.4 to 4.6 p.p.m. The chemical shift of the anomeric proton of methylkasugaminide (5) is located at 4.57 p.p.m. and thus the proton must be axial, excluding structure 8b and 8c in which the anomeric proton is equatorial. Structure 8a is thus completely in agreement with the NMR spectra. 

It is puzzling that the chlorine and other halogen substituents are not known to enhance the sweetness of other sugars, such as methyl -d-glycopyranosides, a,a-trehalose, maltose, or lactose. On the contrary, all of the deoxyhalo sugar derivatives tasted were extremely bitter. The high sweetness of the deoxyhalosucroses is clearly inexplicable in terms of either... 

Scheme 3.23. Radical-mediated domino reaction of glycopyranosides.

U. Aich and D. Loganathan, Stereoselective single-step synthesis and X-ray crystallographic investigation of acetylated aryl 1, 2-trans glycopyranosides and aryl 1,2-cis C2-hydroxy-glycopyranosides, Carbohydr. Res., 341 (2006) 19-28. 

A. K. Misra, P. Tiwari, and G. Agnihotri, Ferrier rearrangement catalyzed by HC104-Si02 Synthesis of 2,3-unsaturated glycopyranosides, Synthesis, 2 (2005) 260-266. 

The Tsuji-Trost reaction is the palladium-catalyzed allylation of nucleophiles [110-113]. In an application to the formation of an A-glycosidic bond, the reaction of 2,3-unsaturated hexopyranoside 97 and imidazole afforded A-glycopyranoside 99 regiospecifically at the anomeric center with retention of configuration [114], Therefore, the oxidative addition of allylic substrate 97 to Pd(0) forms the rc-allyl complex 98 with inversion of configuration, then nucleophilic attack by imidazole proceeds with a second inversion of configuration to give 99. 

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