Catalyzed reaction of triethylborane with pyrazole

The reaction of triethylborane with pyrazole leading to 4,4,8,8-tetraethylpyrazabole was found to be catalyzed by carboxylic acids. 2,2′-Dimethylpropanoic (pivalic) or benzoic acids act as catalysts in this reaction. Intermediates occurring in the catalytic cycle have been isolated and characterized by NMR as well as IR spectroscopy, and in one case also by X-ray crystallography. The mechanism of the reaction is proposed.