Theoretical study of the 1,3-dipolar cycloaddition reactions of azomethineylides. A DFT study of reaction between trifluoromethyl thiomethyl azomethine ylide and acronitrile

The molecular mechanism for the 1,3-dipolar cycloaddition of trifluoromethy l 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 stereos electivity are analyzed and discussed. Analysis of the results on the diffe rent reaction pathways shows that the reaction takes place along a concerte d mechanism, where the two carbon-carbon forming bonds are dissymmetrically formed. This cycloaddition presents a total regioselectivity and endo ster eoselectivity, due to a strong polarization of both dissymmetric dipole and dipolarophile reactants, and a favorable hyperconjugative delocalization t hat appears along the endo approach. Density functional calculations at the B3LYP/6-31G* theory level provide data on transition-state energies for th is 1,3-dipolar cycloaddition in full agreement with the stereochemical outc ome.