Synthesis of 1,3,5-Trisubstituted Pyrazoles Using Aluminum Chloride

Tang et al. have reported the synthesis of trisubstituted pyrazoles from tosylhydrazones (1) and terminal alkynes (2). According to their results, this reaction is promoted by aluminum chloride and regioselectively proceeds to afford 1,3,5-trisubstituted pyrazoles in high yields. Furthermore, various substituents are applicable to R¹ and R² groups like alkyl, allyl, benzyl and propargyl groups as R¹ and aryl groups with electron-donating or -withdrawing groups as R². It is expected to be used in medicinal chemistry.