Regioselective enhancement of the nucleophilicity of the hydroxyl groups in methyl α-l-rhamnopyranoside by complexation with tin(II) chloride

✍ Scribed by Rudolf Toman; František Janeček; Igor Tvaroška; Miroslav Zikmund

• Publisher: Elsevier Science
• Year: 1983
• Tongue: English
• Weight: 543 KB
• Volume: 118
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(83)88031-8

✦ Synopsis

A tentative mechanism for complexation, and a possible model of a tin(II)chlormethyl glycoside intermediate complex, have been established largely from analysis of methyl ethers formed on methylation of methyl cu-L-rhamnopyranoside and its monomethyl ethers by diazomethane in the presence of a catalytic amount of tin(I1) chloride in selected solvents. The complex is mainly formed through displacement of molecules of the donor solvent coordinated to a tin(I1) atom by the favorably c&disposed, hydroxyl groups of the sugar moiety. The spatial arrangement of the hydroxyl groups plus the distribution of atomic charges at the individual oxygen atoms of hydroxyl groups of the methyl glycoside were found to be the main factors responsible for the selectivity observed. The effect of selected solvents on the stability and/or ability to participate in the formation of the foregoing intermediate complex could not be satisfactorily clarified.