NN bridged pyrazoles from nitrogen‐centered radicals: A comparative study of spin densities, molecular structures, and reactivities

Abstract Nitrogen‐centered radicals are versatile synthetic intermediates with the ability to undergo diverse reactions. However, the utility of these reactive species in NN coupling reactions, especially in nitrogen‐rich heterocycles, remains a significant challenge due to the high electronegativity of the nitrogen atoms and the poor molecular stability of high‐nitrogen compounds. In this work, the possibility of NH bond cleavage in different functionalized pyrazoles to produce corresponding nitrogen‐centered radicals was investigated through density functional theory calculations. Based on the calculated results, the NN bridged 4c and 4e were synthesized with expected reaction efficiencies, which were further analyzed by frontier molecular orbital theory. Furthermore, the molecular stability of the synthesized NN bridged bipyrazoles was also studied.