Synthesis of Functionalized 3,4‐Dihydro‐2 H ‐1,4‐Thiazines Through (3 + 3) Cyclization of Pyridinium 1,4‐Zwitterionic Thiolates With 2‐Bromoacetoanilides

ABSTRACT A novel metal‐free (3 + 3) cyclization between pyridinium 1,4‐zwitterionic thiolates and 2‐bromoacetoanilide efficiently synthesizes functionalized 3,4‐dihydro‐2 H ‐1,4‐thiazines. This protocol offers remarkable substrate adaptability, easily prepared substrates and metal‐free catalysis. The findings highlight a practical metal‐free protocol for accessing 3,4‐dihydro‐2 H ‐1,4‐thiazines, circumventing limitations inherent to traditional metal catalysis and demonstrating the potential of 2‐bromoacetanilide in heterocyclic synthesis. Furthermore, biologically significant sulfone analogs are readily accessible via oxidation of the resulting thiazine products using m ‐CPBA.