Showing papers on "Glucal published in 2007"

Acid zeolites as efficient catalysts for O- and S-glycosylation

Abstract: We report herein the first regioselective synthesis of β-galactofuranosides by Fischer glycosidation of GalNAc with methanol catalyzed by HY, HZSM-5 and HBEA acid zeolites. The zeolite HY (Si/Al ratio 3.1) was the most efficient catalyst, leading to the highest yield of methyl β-galactofuranoside, isolated as its acetylated or isopropylidene derivatives, indicating that with large pore zeolites, the reaction efficiency depends upon the concentration of the zeolite acid sites and its hydrophilicity. However, the best regioselectivity for β-galactofuranoside versus β-galactopyranoside was obtained with the medium pore zeolite HZSM-5, which also led to the lowest starting material conversion, suggesting that both the zeolite pore size and topology are determinant for the obtained results. Furthermore, these acid zeolites proved to be efficient catalysts to transform 1,5-anhydro-3,4,6-tri-O-benzyl-2-deoxy- d -arabino-hex-1-enitol (6) (3,4,6-tri-O-benzyl- d -glucal) exclusively in the 2,3-unsaturated-O- and -S-α- d -glycosides by Ferrier rearrangement, in moderate yield. For this reaction, the number of acid sites was the key factor for the reaction yield, being HY (Si/Al ratio 3.1) also the most effective zeolite.

Process for producing glucal

Abstract: The invention relates to the technical field of organic chemistry, in particular to a preparation method of glucal. 1-acetyl glucopyranosyl bromide is added in phosphate buffer solution which contains zinc powder and copper sulfate or the zinc powder and the 1-acetyl glucopyranosyl bromide are added in sodium dihydrogen phosphate water solution, stirring reaction is carried out for 0.5 to 8 hours under the room temperature, then NaOH or KOH is added, the stirring reaction is carried out again for 0.5 to 3 hours under the room temperature, after that, the glucal can be generated. The synthetic method of glucal is also called as a one-pot synthetic method of the glucal and has the advantages of simple operation, shortened process flow, high yield, short reaction time, low cost, less three wastes, small environmental pollution and easy industrialization.

On the alkoxybromination of glucal esters : 2-acetamido-α-d-mannosyl bromides from 2-acetamidoglucal

Abstract: While the alkoxybromination of glucal and 2-acyloxyglucal esters leads to 2-bromo-2-deoxy-α- d -glycosides and α- d -glycosulosyl bromides, respectively, the exposure of 2-acetamido- d -glucal triacetate to NBS/ROH yields 2-O-alkyl-2-C-acetamido-α- d -mannosyl bromides. Although the final products of these reactions are distinctly different, mechanistic considerations show the initial step to consistently be the capture of a bromonium ion by C-2 from the axial side, followed by a trans-addition of ROH. In contrast, fluoro-acetoxylations of the same glucal esters invariably lead to cis-addition products due to a quasi-concerted SET-induced mechanism involving a solvent cage-trapped biradical.

Synthesis of optically pure 4-hydroxymethyl-3-phenoxy-2-azetidinone from D-glucal

Abstract: A convenient approach to enantiomerically pure 4-hydroxymethyl- 3-phenoxy-2-azetidinone has been carried out using the easily available aldehyde 5 as chiral starting material.

Rapid access to in situ generated (R)- and (S)-2-furyloxirane and associated regioselective nucleophilic ring-opening studies

Abstract: Reported herein is the facile preparation of (R)- and (S)-2-furyloxirane from D- and L-tri-O-acetyl glucal and associated regioselective nucleophilic ring-opening studies.

Cobaltpolyoxometalate‐Catalyzed Cyclization of Glucal with Aryl Amines: Synthesis of 2,4‐Disubstituted Tetrahydroquinolines.

Abstract: Treatment of 3,4,6-tri-O-acetyl-d-glucal (1) with various aryl amines in the presence of dodecatungstocobaltate under mild and neutral conditions gave sugar derived tetrahydroquinoline derivates.