Roles of Lewis Acid Catalysts in Diels‐Alder Reactions between Cyclopentadiene and Methyl Acrylate

The Diels‐Alder reaction of cyclopentadiene with methyl acrylate catalyzed by AlCl(3) has been theoretically investigated. M06‐2X level DFT calculations have shown that the formation of two C−C bonds is asynchronous in the cycloaddition both in the endo path and in the exo path, thus making a good contrast to the well‐known concept of [4+2] reactions based on the orbital symmetry arguments. It was found that the catalyst facilitates the cycloaddition and brings a higher endo selectivity in the highly asynchronous process, as compared with the reaction of the diene and the dienophile without the catalyst.