Consequences of the Preeminent Reactivity of 2-OH in Sucrose: Cyclic Acetalation at 2-OH and 3-OH under Basic Conditions

The reaction of unprotected sucrose with tert-butyl chloromethyl ketone in dimethylformamide was investigated as a model for the study of the relative reactivity of the various hydroxy groups of sucrose. Besides the monoethers arising from the substitution of the chlorine atom by 2-OH and 1′-OH of sucrose, the major product is a tert-butyl hydroxymethyl 5-membered ring acetal involving 2-OH and 3-OH. The formation of this product illustrates the preeminent reactivity of 2-OH towards the carbonyl group of the α-chloromethyl ketone, leading to an intermediate hemiacetalic anion, which can enter by intramolecular acetal formation through an intermediate epoxide.