Ligand‐Free Copper(0)‐Catalyzed C−S Ullmann‐Type Cross‐Coupling Reaction: S‐Arylation of 5,4‐Disubstituted 2,4‐Dihydro‐3H‐1,2,4‐triazole‐3‐thiones

We investigated the S‐arylation of 5,4‐disubstituted 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones under ligand‐free Cu(0) catalysis employing Ullmann‐type reaction conditions. We determined optimal reaction conditions and assessed the impact of substituents in the arylating agent on the reaction progress. Notably, the presence of an electron‐withdrawing group (EWG) in the aryl halide facilitated the reaction even without a catalyst. In particular, an EWG in the para position of the aromatic ring exerted a directing effect on the leaving group, regardless of the halogen present. The arylation of 5,4‐disubstituted 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones was investigated under Ullmann‐type reaction conditions involving ligand‐free Cu(0) catalysis, the results of which showed that the reaction proceeds chemoselectively with the formation of S‐arylation products. In some cases, when an electron‐withdrawing group is present in the arylating agent, the reaction can proceed without a catalyst.