Beilstein J. Org. Chem.2017,13, 2385–2395, doi:10.3762/bjoc.13.236
trichloroacetimidate donors using a synergistic catalytic system of electron-deficientpyridiniumsalts/aryl thiourea derivatives at room temperature is demonstrated. The acidity of the adduct formed by the 1,2-addition of alcohol to the electron-deficient pyridinium salt is increased in the presence of an aryl
, the optimized method is also utilized for the regioselective O-glycosylation by using a partially protected acceptor.
Keywords: cooperative catalysis; electron-deficientpyridiniumsalts; O-glycoside; regioselectivity; thiourea; Introduction
The glycosidic linkage is the principal bond present in a
activation at room temperature [32][33][34][35][36]. It is known from the literature that pyridinium salts exhibit pKa values of about 5.2 [37]. Of late, Berkessel et al. disclosed an elegant method, where different electrondeficientpyridiniumsalts (expected pKa values less than 5) were used as a catalyst