DFT study on the mechanism of phosphine-catalyzed ring-opening reaction of cyclopropyl ketones†

In the present study, the mechanism, origin of chemoselectivity, and substituent effects of the phosphine-catalyzed ring-opening reaction of cyclopropyl ketone have been investigated using the DFT method. Multiple pathways, including the formation of hydrofluorenone, the Cloke–Wilson product, and cyclopenta-fused product, were studied and compared. The computational results show that the pathway for the formation of hydrofluorenone is the most favorable one, which involves four processes: nucleophilic substitution to open the three-membered ring, an intramolecular Michael addition for the formation of an enolate intermediate, an intramolecular [1,5]-proton transfer to give ylide, and an intramolecular Wittig reaction to deliver the final product. For disclosing the origin of chemoselectivity, structural analysis and local reactivity index analysis were performed. Moreover, substituent effects were also considered using QTAIM analysis. The current study would provide useful insights for understanding phosphine-catalyzed chemoselective reactions.