Conditions for palladium-catalyzed direct arylations of 4-bromo and 4-iodo N-substituted pyrazoles without C-Br or C-I bond cleavage
Résumé
The Pd-catalyzed arylation at the C5 position of N-protected pyrazole derivs. 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 derivs. 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 chem. transformations are reported.