Metal-Free One-Pot Synthesis of (Tetrahydro)Quinolines through Three-Component Assembly of Arenediazonium Salts, Nitriles, and Styrenes

A highly efficient and convenient metal-free, one-pot synthesis of diversely substituted (tetrahydro)quinolines has been achieved through a three-component assembly reaction of arenediazonium salts, nitriles, and styrenes. In sharp contrast to the prior works with the same reagent blend, the formation of N-arylnitrilium intermediates from arenediazonium salts and nitriles was followed by reaction with styrenes, leading to 3,4-dihydroquinolinium salts as a common intermediate. These could be further transformed to quinolines and tetrahydroquinolines depending on the reaction conditions. The advantages of this protocol include its simplicity, metal-free and mild conditions, readily available starting materials, and good functional group tolerance.