Catalyst-controlled positional-selectivity in C-H functionalizations.

C-H bonds are ubiquitous in organic molecules and typically these bonds are chemically indistinct from each other and it would be highly advantageous for a synthetic chemist to have the ability to choose which C-H bond is functionalized in a given molecule. A controlled and positional-selective C-H bond functionalization is still a prominent goal in this area. With recent developments in transition metal-catalyzed regiodivergent C-H functionalizations, a switch in regioselectivity between two reactive sites within a given substrate is possible under catalytic control, and has profoundly impacted synthetic strategies. Switching site-selectivity within the same or similar precursors represents a great opportunity and challenge in altering the C-H functionalization from one reactive site to other by changing the choice of the catalytic system having a different mechanistic approach. This review discusses the potential and most common approaches employed in tweaking the catalytic systems to alter the positional-selectivity of C-H bond activation.