C–H activation is a ‘simple-to-complex’ transformation that nature has perfected over millions of years of evolution. Transition-metal-catalysed C–H activation has emerged as an expeditious means to expand the chemical space by introducing diverse functionalities. Notably, among the strategies to selectively cleave a particular C–H bond, the catalytic use of a small molecule as co-catalyst to generate a transient directing group, which provides a balance between step economy and chemical productivity, has gained immense attention in recent years. This allows one to convert a desired C–H bond irrespective of its geometrical or stereochemical configuration. This Review describes the various transient directing groups used in C–H activation and explains their mechanistic significance.

C–H 活化是一种“从简单到复杂”的转变，大自然在数百万年的进化过程中不断完善。过渡金属催化的 C-H 活化已成为一种通过引入多种功能来扩展化学空间的快速手段。值得注意的是，在选择性切割特定 C-H 键的策略中，催化使用小分子作为助催化剂以产生瞬态导向基团，从而在步骤经济性和化学生产率之间提供平衡，近年来受到了极大的关注年。这允许人们转换所需的 C-H 键，而不管其几何或立体化学构型如何。本综述描述了 C-H 活化中使用的各种瞬态导向基团，并解释了它们的机理意义。