SO 2 ‐Mediated 2e − , 4e − , and 6e − Reductions: Facile Access to Aryl Amines

Traditional electron‐transfer catalysis frequently requires complex procedures to separate the catalyst from the reaction mixture. In contrast, a concept of a gas‐mediated redox process may offer unique advantages, including its facile removal from the reaction medium. However, such a concept has remained unknown. Addressing this gap, we report the use of the SO 2 gas molecule as an electron‐transfer mediator by generating the sulfur dioxide radical anion (SO 2 •− ) under ambient and chemical conditions. Such SO 2 •− enabled chemoselective, controlled, and scalable multi‐electron reductions (2e − /2H + , 4e − /4H + , 6e − /6H + ) of diverse nitrogen‐containing substrates. Furthermore, the method was successfully applied to the synthesis of clinically active drugs on a multi‐gram scale. Therefore, this work establishes a new paradigm in redox chemistry, demonstrating that a gas molecule can act as an electron‐transfer catalyst, capable of performing reactions that typically require transition metals.