Peculiarities of copper(I)- and palladium-catalyzed cross-coupling of terminal alkynes with vicinal amino- and (N-acetylamino)-iodopyrazoles. Synthesis of alkynylaminopyrazoles

A number of vicinal amino- and (N-acetylamino)-alkylpyrazoles have been syn thesized by cross-coupling reactions of iodopyrazoles with alk-1-ynes using a combination of Pd(PPh3)(2)Cl-2 and CuI as catalyst in Et3N or with coppe r acetylides. The latter Stephens-Castro reaction of copper acetylides with these amino- and (N-acetylamino)-iodopyrazoles was established as a common method for the preparation of (N-acetylamino)alkynylpyrazoles. The Pd/Cu-c atalyzed cross-coupling of iodopyrazoles (Sonogashira reaction) with alk-1- ynes bearing electron-releasing substituents was unsuitable for the synthes is of alkynylpyrazoles: 3- and 5-iodopyrazoles were unreactive but, in the case of 4-iodo derivatives, reductive deiodination, accompanied by homocoup ling of the alk-1-yne component, was the only reaction.