In the phase-transfer-catalyed tosylation of glycoside diols, the ion-pair is formed in the aq. phase and transferred to the org. phase where tosylation occurs. Thus, Me 4,6-O-benzylidene-a-D-mannopyranoside reacted with p-MeC6H4SO2Cl in the presence of Bu4N+HSO4- at room temp. for 30 min to give the 2-O-tosyl deriv. in 95% yield. Me 4,6-O-benzylidene-a- and b-D-glucopyranosides gave similar results with a reaction time of 2 h. [on SciFinder (R)]