Regioselective silylation of C-2 hydroxyl group of α-cyclodextrin dependent on reaction temperature

Silylations of the C-2 hydroxyl group of α-cyclodextrin were carried out using t-butyldimethylsilyl imidazole in the presence of 4 Å molecular sieves in N,N-dimethylformamide. A unique aspect of this silylation method is the temperature dependence of the regioselectivity; silylation at 0°C regioselectively favored the C-6 position to afford mono-6-O-t-butyldimethylsilyl-α-cyclodextrin, whereas silylation at 140°C exhibited high regioselectivity on the C-2 hydroxyl group.