A Simple and Versatile Amide Directing Group for C-H Functionalizations

Achieving selective C-H activation at a single and strategic site in the presence of multiple C-H bonds can provide a powerful and generally useful retrosynthetic disconnection. In this context, a directing group serves as a compass to guide the transition metal to C-H bonds by using distance and geometry as powerful recognition parameters to distinguish between proximal and distal C-H bonds. However, the installation and removal of directing groups is a practical drawback. To improve the utility of this approach, one can seek solutions in three directions: 1)Simplifying the directing group, 2)using common functional groups or protecting groups as directing groups, and 3)attaching the directing group to substrates via a transient covalent bond to render the directing group catalytic. This Review describes the rational development of an extremely simple and yet broadly applicable directing group for Pd-II, Rh-III, and Ru-II catalysts, namely the N-methoxy amide (CONHOMe) moiety. Through collective efforts in the community, a wide range of C-H activation transformations using this type of simple directing group have been developed.