Metal‐ and Additive‐Free One‐Pot Synthesis of 2,3,5‐Trisubstituted 1,3,4‐Thiadiazines Using β‐Ketodithioesters and 2‐Bromohydrazones through a Cross‐Coupling/Cyclization Cascade

Privileged 2,3,5‐trisubstituted 1,3,4‐thiadiazines were synthesized from readily accessible β‐ketodithioesters as a two‐atom (CS) synthon and 2‐bromohydrazones as a four‐atom (CCNN) unit through a cross‐coupling/cyclization cascade. The operationally simple metal‐ and additive‐free method shows broad substrate scope as well as high functional‐group tolerance and provides a direct route to functionalized 1,3,4‐thiadiazines that are not easily prepared by other methods. This one‐pot approach features easy‐to‐handle nontoxic reagents, high yields, gram scalability, excellent selectivity and the formation of an exocyclic double bond with Z‐stereoselectivity.