Regioselectivity shift from β-(1→6)- to β-(1→3)-glycosylation of non-protected methyl β-d-galactopyranosides using the stannylene activation method

Regio- and stereoselective glycosylation of non-protected methyl β-d-galactopyranoside has been developed using the stannylene acetal mediator, allowing a one-pot assembly of glucosyl-β-(1→6)-galactose and glucosyl-β-(1→3)-galactose. Remarkable regioselectivity shift from β-(1→6)- to β-(1→3)-glycosylation has been observed by addition of Bu4NF etc. to the reaction medium. The method requires no tedious, lengthy manipulation being employed for the conventional protection–deprotection method.