Glycosylation of the 'armed' thioglycoside with various glycosyl accepters is promoted by using a combination of stoichiometoric amount of N-(ethylthio)phthalimide (PhthNSEt) and catalytic amount of trityl tetrakis(pentafluorophenyl)borate [TrB(C6F5)(4)], and is successfully applied to one-pot 'armed-disarmed' sequential synthesis of trisaccharides.