Theoretical Study of the 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides. A DFT Study of Reaction between Trifluoromethyl Thiomethyl Azomethine Ylide and Acronitrile

The molecular mechanism for the 1,3-dipolar cycloaddition of trifluoromethyl thiomethyl azomethine ylide with acronitrile has been characterized using density functional theory methods with the B3LYP functional and the 6-31G* and 6-31+G** basis sets. Relative rates, regioselectivity and endo stereoselectivity are analyzed and discussed. Analysis of the results on the different reaction pathways shows that the reaction takes place along a concerted mechanism, where the two carbon−carbon forming bonds are dissymmetrically formed. This cycloaddition presents a total regioselectivity and endo stereoselectivity, due to a strong polarization of both dissymmetric dipole and dipolarophile reactants, and a favorable hyperconjugative delocalization that appears along the endo approach. Density functional calculations at the B3LYP/6-31G* theory level provide data on transition-state energies for this 1,3-dipolar cycloaddition in full agreement with the stereochemical outcome.