Two approaches to the synthesis of 3-β-d-glucopyranosyl-d-glucitol

Glycosidation of 1,2:5,6-di-O-isopropylidene-d-glucose with tetra-O-acetyl-glucosyl bromide in 1:1 benzene–MeNO2 afforded approximately equal amounts of the 3-O-β-d-glycoside and the rearranged 6-O-β-d-glycoside, while in MeCN only the latter was formed. When tetra-O-acetyl-β-thiophenylglucoside was used as donor in CH2Cl2 in the presence of NIS/TfOH as activator, the 6-O-β-d-glycoside and a 3-O-orthoester were formed in a 1:2 ratio at −20 °C, while at 20 °C only the former could be isolated. Glycosidation of 1-O-benzoyl-2,4-O-benzylidene-5,6-O-isopropylidene-d-glucitol with tetra-O-acetyl-glucosyl bromide in MeCN in the presence of Hg(CN)2 afforded the corresponding 3-O-α- and 3-O-β-glycopyranoside in a 1:4 ratio in MeCN and 1:5 in 1:1 benzene–MeNO2, respectively. When Hg(CN)2/HgBr2 was used as promoter, the corresponding orthoester was also formed. When tetra-O-acetyl-β-thiophenylglucoside was used as donor, the 3-O-β-anomer and the orthoester were obtained predominantly in a 3:2 ratio together with traces of the 3-O-α-glycoside. Both β-glycosides could be smoothly converted into 3-β-d-glucopyranosyl-d-glucitol.