How does HOTf/HFIP Cooperative System Catalyze the Ring-Opening Reaction of Cyclopropanes? A DFT Study

Density functional theory calculations have been performed to probe the detailed mechanisms of Bronsted-acid-catalyzed ring-opening reactions of donor-acceptor cyclopropanes. The reaction model without consideration of the explicit solvation effect was characterized by a high activation free energy of 29.5 kcal/mol, while inclusion of the explicit solvation effect in calculations lowered the activation free energy to 20.5 kcal/mol, which demonstrated the cooperative role of HOTf and HFIP in facilitating the ring-opening step. Additionally, we put forward two distinct reaction mechanisms, including the nucleophile-induced mechanism and the protonation-induced mechanism, for the ring-opening step of donor-acceptor cyclopropanes. Computational results revealed that modulation of the reaction conditions could result in the shift of the reaction mechanisms.