Conditions for palladium-catalyzed direct arylations of 4-bromo and 4-iodo N-substituted pyrazoles without C-Br or C-I bond cleavage

The Pd-catalyzed arylation at the C5 position of N-protected pyrazole derivatives bearing bromo or iodo substituents at the C4 position is described. A simple phosphine-free catalytic system was used, namely, 1 mol% Pd(OAc)(2) in DMA in the presence of KOAc as the base. A wide aryl bromide scope as a coupling partner has been coupled with pyrazole derivatives. The reaction was very chemoselective as the C-halogen bonds of the pyrazole units were not involved in the C-H bond arylation process. Some examples demonstrating the synthetic potential of the bromo and iodo pyrazole substituents for chemical transformations are reported.