Reversing conventional site-selectivity in C(sp3)-H bond activation.

One of the core barriers to developing C-H activation reactions is the ability to distinguish between multiple C-H bonds that are nearly identical in terms of electronic properties and bond strengths. Through recognition of distance and molecular geometry, remote C(sp2)-H bonds have been selectively activated in the presence of proximate ones. Yet achieving such unconventional site selectivity with C(sp3)-H bonds remains a paramount challenge. Here we report a combination of a simple pyruvic acid-derived directing group and a 2-pyridone ligand that enables the preferential activation of the distal γ-C(sp3)-H bond over the proximate β-C(sp3)-H bonds for a wide range of alcohol-derived substrates. A competition experiment between the five- and six-membered cyclopalladation step, as well as kinetic experiments, demonstrate the feasibility of using geometric strain to reverse the conventional site selectivity in C(sp3)-H activation.