Kinetico‐Mechanistic Studies of Cu(II)‐Mediated Cyclization of Imines via C−H Bond Activations.

Herein, we focus on the kinetico‐mechanistic studies of a carboxylate and Cu(II)‐assisted synthesis of imidazo[1,5‐a]pyridines encompassing C(sp3)−H amination and cyclization of imines coupled with C(sp2)−H cyanation using time‐resolved UV‐Vis reaction monitoring and ex‐situ analyses. Thus, kinetic studies have been carried out, providing a proof of the elementary steps involved, allowing for batch analysis of the compounds present in solution via MS. The experimental data obtained are consistent with the formation of a cyclometalated complex (k1) involving a C(sp3)−H bond cleavage followed by a reductive elimination/proton abstraction event (k2), both showing high enthalpy‐demanding transition states. The two processes show a well‐defined Eyring behavior with values of ΔH≠ and ΔS≠ within the expected range. Further insights on the intermediate fast C(sp2)–cyanation are also presented together with control reactions. [ABSTRACT FROM AUTHOR]