3-Methyl-1-phenyl-4-thioaroylpyrazolones—Synthesis, Preferred Solid-State Geometry and an Atypical Side Product of Lawesson’s Thionation

A series of five novel 3-methyl-1-phenyl-4-(4-thioaroyl)-pyrazol-5-ones is obtained in excellent yields by thionation of the corresponding O-analogues with Lawesson’s reagent. The products are characterized in solution and solid phase. It is found that only mono-thionation occurs and that the products exist in enol-thione forms. Atypical side products are isolated and characterized. The preferred solid state forms are analyzed and compared with those of the corresponding O-analogues.