Electrochemical Oxidative C(sp 3 )−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(sp 3 )−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(sp 3 )−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.