Pyrazolyldiazonium Salts in the Synthesis of 4‐Amino‐1,3’‐bipyrazoles

Abstract

An efficient protocol for the synthesis of fluorescent 4‐amino‐1,3′‐bipyrazoles, which are substituted at the positions N‐1′, C‐4′, 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.