A Transition Metal-Free Strategy for Dihydrobenzazepinoindole via KI-Mediated Oxidative Pictet-Spengler Reaction

A transition-metal-free synthesis of dihydrobenzazepinoindoles has been developed using a potassium iodide (KI)-mediated oxidative Pictet-Spengler reaction under mild conditions. While the classical Pictet-Spengler cyclization is well-established, its oxidative variant remains underexplored. This method offers a sustainable and efficient approach, providing operational simplicity, broad substrate scope, and enhanced environmental compatibility. The reaction tolerates various functional groups, enabling access to structurally diverse dihydrobenzazepinoindole derivatives. The synthesized compounds were fully characterized using 1H NMR, 13C NMR, DEPT-135, IR, and mass spectrometry, confirming their structural integrity. The scalability of this method has been demonstrated through a successful large-scale synthesis. A plausible reaction mechanism has been proposed, shedding light on the role of KI in the oxidative cyclization. This study underscores the potential of KI as an environmentally benign promoter and presents a practical alternative to traditional metal-mediated methodologies for the synthesis of nitrogen-containing heterocycles.