Development of Transition-Metal-Catalyzed C(sp2)-H Functionalization of Arenes with Diazo Compounds

C-H bond functionalization has been one of the most important subject in chemistry. How to control the site selectivity of C-H bond is the key issue and remain challenge. Transition-metal-catalyzed organic tranformation of diazo compounds, such as X-H (X=O, N, S, etc.) insertion, cyclopropanation, cross-coupling reactions and C(sp(3))-H functionalization, have been well established, whereas the C(sp(2))-H functionalization using diazo compounds is less developed. This review will summarize the progress in transition-metal-catalyzed C(sp(2))-H functionalization of arenes with diazo compounds. To realize the site selectivity, two strategies are utilized. One is directed C-H activation, which gives the ortho-selective CH functionalization products. The other is undirected approach, which normally exhibits para-selectivity. In order to understand these reactions, the mechanisms for selected examples are also provided.