Metal-free Cross-Dehydrogenative Coupling of HN-azoles with α-C(sp3)-H Amides via C-H Activation and Its Mechanistic and Application Studies.

Abstract

A metal-free one step coupling reaction between various N-azole rings and diverse α-C(sp3)-H containing amides has been developed under oxidative reaction conditions. Commercially available tetrabutyl ammonium iodide (TBAI) in the presence of terbutylhydroperoxide (TBHP), under neat reaction condition, efficiently catalyzed the coupling. Various azole types, such as 1H-benzotriazoles, 1H-1,2,3-triazoles, 1H-1,2,4-triazoles, 1H-tetrazoles, 1H-pyrazoles, and 1H-benzimidazoles, and α-C(sp3)-H containing amides, such as N,N-dimethylacetamide, N,N-dimethylbenzamide, N-methylacetamide, N,N-diethylacetamide, N-methylpyrrolidine, and pyrrolidine-2-one, were successfully employed for the coupling. A series of designed and controlled experiments were also performed in order to study the involvement of the different intermediates. Based on the evidence, a plausible mechanism is also proposed. These novel, simple, rapid, attractive, and straightforward transformations open the way of the construction of novel highly functionalized N-azoles via direct covalent N-H bond transformations onto N-C bonds. This approach allows to the synthesis of complex molecules requiring number of steps using classical synthetic ways. In addition, the range of α-C(sp3)-H containing amide substrates is virtually unlimited highlighting the potential value of this simple system for the construction of complex heterocyclic molecules, such as fused azoles derivatives.