Phenyl tetra-O-benzoyl-1-telluro-β-D-glucopyranoside, when treated with 1,2:3,4-di-O-isopropylidene-α-D-galactose in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid, immediately forms the expected β-disaccharide derivative. A subsequent experiment involving both a telluroglycoside and a selenoglycoside as donors with the one alcohol acceptor showed complete preference for the telluroglycoside. This result has led to an extension of the investigation to establish a ‘reactivity scale’ for various telluro, seleno and thio sugars.