Regioselective Synthesis of 1,3,5-Trisubstituted Pyrazoles from N-Alkylated Tosylhydrazones and Terminal Alkynes

An efficient synthesis of 1,3,5-trisubstituted pyrazoles from N-alkylated tosylhydrazones and terminal alkynes was developed. The protocol was applied to a wide range of substrates and demonstrated excellent tolerance to a variety of substituents, including both electron-donating and -withdrawing groups. In comparison with the common approaches for substituted pyrazole syntheses, this methodology proceeded with complete regioselectivity, especially, in the cases that R2 and R3 are similar substituents.