Synthesis of N-Arylpyrazoles by Palladium-Catalyzed Coupling of Aryl Triflates with Pyrazole Derivatives.

A method for the synthesis of N-arylpyrazoles by palladium-catalyzed coupling of aryl triflates with pyrazole derivatives is described. Using tBuBrettPhos as a ligand, the palladium-catalyzed C-N coupling of a variety of aryl triflates including ortho-substituted ones with pyrazole derivatives proceeded efficiently to give N-arylpyrazole products in high yields. 3-Trimethylsilylpyrazole was found to be an excellent pyrazole substrate for the coupling, and the corresponding product, 1-aryl-3-trimethylsilylpyrazole, also served as a great template for the syntheses of N-arylpyrazole derivatives, as demonstrated by regioselective halogenation at the 3-, 4-, and 5-positions of the pyrazole ring.