Copper-Catalyzed C(sp3)-H Methylation via Radical Relay

The methyl moiety is a key functional group that can result in major improvements in the potency and selectivity of pharmaceutical agents. We present a radical relay C-H methylation methodology that employs a beta-diketiminate copper catalyst capable of methylating unactivated C(sp(3))-H bonds. Taking advantage of the bench-stable DABAL-Me-3, an amine-stabilized trimethylaluminum reagent, methylation of a range of substrates possessing both activated and unactivated C(sp(3))-H bonds proceeds with a minimal amount of overmethylation. Mechanistic studies supported by both experiment and computation suggest the intermediacy of a copper(II) methyl intermediate reactive toward both the loss of the methyl radical as well capture of radicals R-center dot to form R-Me bonds.