Pyrazolyldiazonium salts in the synthesis of 4-amino-1,3’-bipyrazoles

An efficient protocol for the synthesis of fluorescent 4-amino1,3’-bipyrazoles, which are substituted at the positions N-1’, C4’, C-3 and C-5, is described. By a two-step synthetic strategy, an initial azo coupling of ethyl cyanoacetate and various 1- alkylpyrazolyldiazonium chlorides gave substituted ethyl 2- cyano-2-(2-(pyrazol-3-yl)hydrazine-ylidene)acetates, which were subsequently subjected to Thorpe-Ziegler type cyclisation reactions to yield the title compounds.