Abstract: A novel, efficient glycosylating reagent, R 3,4-O-isopropylidene-2-O-(4-methoxybenzyl)-1-thio-.beta. -L-fucopyranoside wherein R is a lower alkyl or lower alkenyl of 1 to 8 carbons such as methyl or pentenyl, is described. This novel reagent provides for the facile synthesis of linear and other .alpha.-L-fucosyl oligosaccharides. In addition, a method for the preparation of 2'-O-.alpha.-L-fucopyranosyl-lactose, which comprises reacting the abovementioned glycosylating reagent with solvated 4-O-(6-O-acetyl-3,4-O-isopropylidene-.beta.-D-galactopyranosyl)-2,3,5,6-di -O-isopropylidene-D-glucose, dimethyl acetal, a tetrabutylammonium halide and a catalyst and then de-O-acetylating the resulting reaction product with sodium methoxide methanol, is also disclosed.