Direct Regioselective Esterification at O-2 of β-Cyclodextrin and Hydrolysis by Neighboring-group Participation
A simple and efficient strategy for direct regioselective esterification at O-2 of β-cyclodextrin was developed by using the combination of N,N'-carbonyldiimidazole and carbonate buffer in 1,4-dioxane, which does not require large amounts of polar organic solvents such as DMF, toxic solvents such as CH3CN, or flammable bases such as NaH. Moreover, their hydrolyses by neighboring-group participation were observed. Mono-2-tosyl-β-cyclodextrin was liable to epoxidation, while mono-2-(p-methylbenzoyl)-β-cyclodextrin liable to isomerization. They had different mechanisms of hydrolysis.