Transition-metal Catalyzed 1,2,3-Triazole-assisted C—H Functionalization Processes

1,2,3-Triazole derivatives are a kind of N-containing heterocyclic compounds with important biological activities, which have widespread applications in diverse fields such as pharmaceuticals, pesticides, and materials. Therefore, it is of great significance to continuously develop new structures based on triazole framework and to find new and efficient synthetic methods of triazole derivatives. Although 1,2,3-triazole compounds are widely used, there is no report that 1,2,3-triazole compounds directly come from natural products. All of 1,2,3-triazoles and their dirivatives are artificially synthesized by chemical methods. Various strategies for their synthesis have been devised, with Huisgen 1,3-dipolar [3+2] cycloadditions of azides and alkynes being the most commonly used approach. However, this methodology, in most cases, leads to the formation of a mixture of regioisomeric products and requires the presence of a strong electron-withdrawing substitutent at the alkyne. Later, Fokin and Sharpless reported Cu(I)-catalyzed regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles. This "click" reaction proceeded highly regioselectively when using terminal alkynes affording 1,4-disubstituted 1,2,3-triazoles in excellent yield. In recent years, transition-metal catalyzed C-H bond activation has attracted attention from scientists worldwide, and has become an important protocol for the construction of carbon-carbon bonds and carbon-heteroatom bonds in organic synthesis owing to its facile manipulation, high efficiency and less waste. An important strategy to realize the regioselectivity of the C-H activation is to use the auxiliary function of the directing group. Recently, transition-metal catalyzed 1,2,3-triazole-assisted C-H functionalization has been widely concerned by scientists. In this stragety, 1,2, 3-triazoles with different structures were used as guiding groups to construct new C-C and C-X bonds by direct conversion of C-H bonds under different reaction conditions to access more complex triazoles since many simple triazoles can be easily obtained via click reaction. In this perspective article, we will briefly summarize the advance in the field of transition-metal catalyzed 1,2,3-triazole-assisted C-H functionalization according to the bonding type, including carbon-carbon bond, carbon-heteroatom bond and annulation. The advantages and disadvantages of different kinds of directing groups are discussed. Meanwhile, pathways for future development have been proposed.