Bifunctional Catalysts on desymmetrization reaction of anhydrides: ONIOM study

초록

The reaction between anhydride and methanol catalyzed by bifunctional Bronsted acid/base organocatalyst was investigated theoretically by ONIOM method. Calculations indicate that the energy barrier is quite high without catalyst, i.e. 30.8 kcal/mol. In the presence of catalyst, the reaction proceeds through a 2-step mechanism an energy barrier of 19.0 kcal/mol and 0.9 kcal/mol. The pyridine moiety works as a Bronsted base to activate methanol substrate, and the N atom attached to P atom as a Bronsted acid to activate the anhydride by hydrogen bonding. The role of enantioselectivity of the catalyst is consistent with experiment results.