A DFT study on the reaction mechanisms of ketene–ketone [2 + 2 + 2] cycloaddition to form 3-aryglutaric anhydrides under a Lewis acid catalysis: What is the role of BF3?

The mechanisms of the title reaction have been studied by density functional theory (DFT). Three possible reaction channels, including one non-catalyzed channel (channel 1) and two channels promoted by Lewis acid BF3 (channels 2 and 3) are shown. The calculated results indicate that one of the catalyzed channels (channel 2) is most energy favorable among all the three channels, so it occurs more often than others. To the best of our knowledge, why Lewis acids can lower the energy barrier of ketene–ketone cycloaddition largely has still been ambiguous by now. In order to clarify the puzzle, we have used an effective method of frontier molecular orbital (FMO) analysis to explain how the Lewis acid BF3 make the reaction easier to occur. The results revealed that in addition to the orbital symmetries and the energy gaps between the frontier molecular orbitals, the different overlap modes of the frontier molecular orbitals are also important for the reaction in this paper.

Graphical abstractWhy can R1 react with R2 to generate P under the BF3-catalyzed condition? What is the role of Lewis acid BF3? In this paper, we have investigated the mechanisms of the title reaction.Figure optionsDownload full-size imageDownload high-quality image (77 K)Download as PowerPoint slide