Recent advances in N-heterocycles synthesis through catalytic C-H functionalization of azobenzenes

Azobenzenes are well known as crucial structural motifs used in material sciences, nonlinear optical devices, and pharmaceuticals. They also represent an important class of organic intermediates for the transformation of azo and azoxy groups into various useful molecules. Azo groups have a dual character, both electronically increasing the reactivity of the aryl ring and controlling the site-selectivity of the reaction, which significantly increases their utility in organic synthesis. As a complement to previous protocols, the strategy of transition-metal-catalyzed C-H activation of azobenzenes using various coupling partners, such as alkenes, alkynes, aldehydes, diazo esters, organic azides, and sulfoxonium ylides, has recently emerged as a powerful tool to create the corresponding heterocycles. Thus, this review focuses on the recent progress on the direct synthesis of N-heterocycles via C(sp(2) )-H functionalization of azobenzenes using transition-metal catalysis. This review includes most of the reported methods until the beginning of 2018. (C) 2018 Elsevier Ltd. All rights reserved.