One-pot synthesis of 2,2′-biquinolines from aromatic amines using oxygen as an oxidant under metal-free conditions†

We have developed an efficient method for the synthesis of unsymmetrical and symmetrical 2,2′-biquinoline derivatives under 55% HI-catalyzed conditions using oxygen as the oxidant and cheap and readily available aromatic amines as feedstocks in one pot. This transformation undergoes multistep reactions such as multiple radical additions and isomerization, cyclization, and oxidation. Mechanistic investigations indicate that the transformation may involve a free radical cascade cyclization pathway.