Reactivity of diazoazoles with electron-rich double bonds

Abstract

The energies of several intermediates that could arise from the reaction of diazoazoles with alkenes have been estimated by means of the MNDO and AM1 SCF-MO methods as well as, in some cases, by means of ab initio methods, at the 3-21G level. All the nine possible unsubstituted diazoazoles have also been calculated by MNDO and their similarities and differences, among them and with regard to diazomethane and 4,5-dicyano-2-diazo-2H-imidazole, have been discussed. The calculations suggest a 1,4-dipole behaviour (also viewed as a 1,7-dipole behaviour) for most diazoazoles when reacting with electron-rich alkenes; it is believed that the approach between 2-diazo-2H-imidazole and alkenes to give rise to the [4 + 2]-cycloadducts is quite asynchronous. Finally, some errors found in the literature concerning the reactivity of diazoazoles with alkoxy-ethenes have been corrected, while the reactivity of certain diazoazoles with conjugated dienes to afford N-azolodihydropyridazines rather than azolotriazine derivatives (via‘reverse electron demand’ cycloadditions) has been confirmed.