C-H Functionalization offers the potential for streamlined and improved processes in the synthesis of valuable organic compounds. Directing groups have provided an effective means to control site-selectivity between numerous similar C-H bonds in C-H functionalization, by correctly locating a transition metal and promoting proximity driven C-H activation. However, the requirement for amide bound directing groups continues to present an intrinsic efficiency limitation, due to the additional discrete steps required to install and remove these groups. Recently transient directing groups (TDGs) have been developed, notably for arylation processes, whereby the directing group is formed and removed within the C-H functionalisation reaction by taking advantage of common valuable functional groups such as aldehydes (Figure ). Transient directing groups formed as imines have been used in particular to selectively functionalize aldehyde or amine components, though in a limited range of transformations to date. A transient directing group approach was first described by Jun for the alkylation of aldehydic C-H bonds. In 2016, Yu reignited interest in this field by demonstrating powerful benzylic and sp C-H functionalization of aldehydes and ketones respectively using co-catalytic palladium acetate and glycine to form a transient coordinating imine. In 2017, Yu reported the palladium catalyzed transient ortho-C-H functionalization of benzaldehydes, achieving arylation, bromination and chlorination with imines derived from anilines (Figure ). Contemporaneously, Sorensen developed C(sp 2 )-H hydroxylation, fluorination and methylation processes. Noticeably there are no examples of C-S bond formation using transient C-H functionalization. Furthermore, the majority of transient directing groups use precious metal catalysis, mainly palladium, but also rhodium, ruthenium and iridium. The move towards more sustainable, earth abundant metals presents a notable challenge in C-H functionalization, due in part to the poor mechanistic understanding of base metal mediated processes making rational reaction optimization particularly challenging. To date there are only two reports of 3d metals being used for C-H functionalisation in combination with TDGs, both in cobalt catalysed amidation. Specifically, there are no examples of copper mediated C-H functionalization with TDGs.