Mild Conditions for Copper‐Catalysed N‐Arylation of Pyrazoles

Copper‐catalysed N ‐arylation of pyrazoles with aryl or heteroaryl bromides or iodides, which can include functional substituents, was performed under the mildest conditions yet described, with excellent yields and selectivity, by the use as catalyst of a combination of cuprous oxide with a set of inexpensive, chelating oxime‐type ligands not previously known to promote such reactions. Other original bi‐, tri‐ or tetradentate ligands providing nitrogen and/or oxygen as chelating atoms were also successfully tested in this type of arylation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)