Synergistic Effects between Lewis and Bronsted Acids: Application to the Prins Cyclization

Bronsted and Lewis acids can catalyze the Prins cyclization, an efficient method for the synthesis of tetrahydropyrans from homoallylic alcohols and carbonyl compounds. Synergistic effects between weak Bronsted and Lewis acids in these reactions have been analyzed by density functional theory [M06-L/def2-QZVP/IEFPCM(CH2C12)// M06-L/6-311+G(2df,2p)]. In order to characterize the reactivities of the employed Lewis acids, methyl anion and hydroxide affinities were determined. On the basis of our calculations, we found that the coordination of Lewis acids to carboxylic and sulfonic acids results in a significant increase in the Bronsted acidities of the latter.