MECHANISM OF METHYLATION OF NUCLEOSIDE SUGAR HYDROXYL GROUPS BY DIAZOMETHANE IN THE PRESENCE OF STANNOUS CHLORIDE

Article abstract of DOI:10.1016/S0008-6215(00)80988-X

Diazomethane rapidly reacts with SnCl2 in methanol to give MeCl and Sn(OMe)2, both of which were isolated and identified.This reaction is the initial step in the apparent SnCl2*2H2O-catalysed methylation of nucleoside by diazomethane.The actual catalyst, Sn(OMe)2, readily reacts with Broensted acids, with exchange of ligands.For ribofuranosyl nucleusides, Sn2+ binds to site(s) having a labile proton, the effect being particulary predominant with 5- and 6-membered cyclic structures, with the tin ion co-ordinated to the ionised hydroxyl groups of the sugar moiety.These cyclic structures account for the high reactivity of the hydroxyl groups towards Me+, as in the complexes of ribofuranosyl nucleosides with Bu2SnO.A similar, if not identical, mechanism operates in the case of glucopyranosides.