Electrochemical Oxidative C(sp3 )-H/N-H Cross-Coupling for N-Mannich Bases with Hydrogen Evolution.

N-Mannich bases are an important structure in various functional molecules. A new protocol to synthesize N-Mannich bases was established through electrochemical external-oxidant-free C(sp3 )-H/N-H cross-coupling with hydrogen evolution. Various N-methylanilines were explored in this transformation. Moreover, simple amides, heteroatom-containing amides, and succinimides were well tolerated in moderate-to-good yields. In addition, the electrochemical dehydrogenative C(sp3 )-H/N-H cross-coupling could be scaled up to 5 mmol. By using triethyl phosphite as trapping agent, the phosphorylation product was detected. At the same time, kinetic isotope effect experiments showed that the cleavage of the C-H bond is the rate-limiting step.