Chartelline C, a marine alkaloid, possesses a unique core scaffold including indolenine β-lactam and imidazole moieties linked by an unsaturated 10-membered ring. A new synthetic approach for the construction of the indolenine β-lactam was planned, based on the inherent reactivity of chartelline A with NaOMe, triggered by bromination of bromoenamide, and proceeding through an N-acyl imine. However, the N-acyl imine intermediate was not observed. Instead, the corresponding bromoindolenine was obtained, which led to the desired indolenine β-lactam in 92% yield.