Glucopyranoside, alkyl 3 anomer

The conformational anomeric effects design the contrasteric effects observed in acetals which render the more sterically encumbered gauche/ gauche conformers more stable than their anti/gauche and anti/anti conformers. Such effects were first evidenced by Jungins in 1905 and rediscovered by Edward in 1955 and by Lemieux and Chiu in 1958. They observed the higher stability of alkyl a-D-glucopyranosides in comparison with their (3-anomers (Fig. 5).8... 

Koenigs-Knorr synthesis. This catalyst system can be used in place of the usual silver oxide or silver carbonate in synthesis of alkyl -D-glucopyranosides, 3-D-galactopyranosides, and /3-D-xylopyranosides. The j3-anomers are formed almost exclusively in yields of 60-80%. The reaction is conducted in absolute chloroform in the presence of Drierite reactions are complete in 1-2 hr. at 25°. ... 

The effect of Q-alkylation on the anomeric solution equilibrium of D-glucopyranose and of methyl D-glucopyranoside has been studied. A considerable increase in the proportion of a-anomer for 2-Q-methyl-D-glucopyranose was observed, but there was no change for methyl D-glucopyranoside on Q-alkylation. A method has been reported for the preparation of all of the methyl ethers of methyl 2-acetamido-2-deoxy-a-D-glucopyranoside. Methylation of methyl (methyl o-D-mannopyranosid)uronate, methyl (methyl o-D-glucopyranosid)uronate, and methyl (methyl p-D-... 

Treatment of alkyl l-thio-j3-D-glucopyranoside tetra-acetates with boron tri-fluoride in dichloromethane at room temperature afforded mixtures of the a-and jS-anomers, in the ratio of ca. 7 3, which were readily separated by chromatography on silica gel. Boron trifluoride also catalysed the condensation of equimolar proportions of 1,2-/rflnj-related monosaccharide peresters and alkyl, alkenyl, and some aryl thiols to provide a convenient synthesis of esters... 

---