An efficient potassium carbonate-mediated tandem C–S and C–N coupling reaction between N-(2-iodophenyl)acetamides and 2-halo-benzenethiols has been developed. This protocol affords a simple and efficient approach for the construction of phenothiazine derivatives without the need for addition of transition-metal catalyst or ligand for the first time. Furthermore, the reaction can be easily performed on a large scale.