Kinetic Products Under Thermal Conditions: Rapid Entry into α/β-D-Galactofuranosides Using Microwave Irradiation and Selective Lewis Acids

Abstract

A modified Fischer-Lubineau reaction, employing microwave irradiation and selected Lewis acids such as Mn(ClO 4 ) 2 , Mn(C 2 H 3 O 2 ) 3 , FeCl 3 , CoCl 2 , and AgF as independent additives, induces rapid entry into α/β-D-galactofuranosides in very good yield and purity.

Solvent Polarity-Controlled Selective Synthesis of Methyl Pyranoside and Furanoside

“…Alkyl furanosides have been synthesized as the major products in solvents less polar than methanol, which has been attributed to metal complexions with the sugars because these glycosylation are often catalyzed by metal salts. 20 A plausible mechanism for the synthesis of methyl D-glucofuranoside is shown in Figure 1. First, the reaction of DMSO with TCT leads to I, which is attacked by the C-1 hydroxyl group of D-glucofuranose to form II.…”

“…The reported yields of methyl D-galactopyranoside synthesized using microwave irradiation are 100% 42 and 84%. 41 Two methods for the synthesis of methyl D-galactofuranoside as a major product catalyzed by FeCl 3 (furanoside:pyranoside = 75:20) 20 and in 75% yield are known. 12 Our method has better selectivity for furanoside.…”

“…The reaction yield of acetone and sugar for 1,2:5,6-di-isopropylidene-α- d -glucofuranose is >90%. For the other currently used preparation methods, the highest reported yields for d -glucofuranoside are all <80%, ,, and these products have to be separated from their isomer glucopyranoside (produced in >20% yield). The reason that 2 and 3 can be separately synthesized as the sole product with this method is probably because methanol is more polar than DMSO, and presumably when the concentration of DMSO in methanol is lower, the reaction medium is more polar and the d -glucose exists in the furanose form.…”

“…These results indicate that the solvent polarity is critical to the ratio of furanoside and pyranoside because all of these higher alcohols are less polar than methanol. Alkyl furanosides have been synthesized as the major products in solvents less polar than methanol, which has been attributed to metal complexions with the sugars because these glycosylation are often catalyzed by metal salts …”

Kinetically Controlled Fischer Glycosidation under Flow Conditions: A New Method for Preparing Furanosides

“…sides ratio and their α/β isomerization changed depending on the Lewis acid used. 12 The addition of CaCl 2 also improved the selectivity toward β-furanosides. 13 However, the generation of a certain amount of pyranosides is inevitable.…”