Transition Metal‐Catalyzed CH Functionalizations Using a Transient Directing Group Approach

Transition metal-catalyzed CH bond functionalization reactions are among the cutting-edge synthetic tool for step-economical construction of complex-molecular architectures. In this realm, the key challenge lies in harnessing the site-selective activation of the inert CH bonds. Although covalently tethered directing groups rendered reliable results in obtaining positional selectivity, their preinstallation and removal entail multiple steps restricting their applicability. An alternative approach is developed to fill this gap where a transient ligand enables the formation of the directing group in situ and dissociates after the reaction's completion. This strategy is widely known as the transient directing group (TDG) approach. Diverse functionalization such as arylation, alkylation, amination, halogenation, etc., could be achieved using TDG as a powerful means. Moreover, asymmetric functionalization has also been realized utilizing this technique. However, this strategy remained only applicable to aldehydes, ketones, amines, and phenol substrates.