Abstract
Acetonation of d-glucose with 2,2-dimethoxypropane in N,N-dimethyl-formamide containing a trace of p-toluenesulfonic acid at room temperature gave 4,6- O-isopropylidene- d-glucopyranose almost exclusively. However, when this reaction was conducted at 95°, 5,6- O-isopropylidene- d-glucofuranose, 1,2:5,6-di- O-isopropylidene-α- d-glucofuranose, and an acyclic di- O-isopropylidene derivative were obtained as major products. Such variation of products with temperature presumably reflects pyranose-furanose equilibria in which d-glucose exists mainly in the pyranose forms at room temperature, but in the furanose and acyclic ones at 95°; this suggests that this reaction is controlled kinetically, with favored attack by the reagent at the primary hydroxyl group.
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