THE REACTIONS OF 1,2,3-TRIAZOLIUM-1-IMIDES WITH DIPOLAROPHILES - KINETICS AND MECHANISM - AZOLIUM 1,3-DIPOLES

The reactions of substituted 1,2,3-triazolium-1-imides with dipolarophiles are dipole-HOMO controlled concerted cycloadditions. The second-order rate constants are insensitive to solvent polarity and the reaction shows a high negative entropy of activation. Substituent effects at the triazole carbon terminus of the dipole show a linear Hammett-sigma(p) correlation with p = 1.51. Substituents at the N-terminus of the dipole show a rare inverted V-type Hammett correlation with the reaction being dramatically inhibited by both MeO and NO2 groups. Dipolarophile variation suggests that triazolium imides are Type I dipoles. The regioselectivity of the reactions agree with ab initio calculated orbital coefficients and HOMO and LUMO energies.