Reaction of β-amino-α,β-unsaturated esters and amides with aryl diazonium salts : Synthesis of cinnoline derivatives

Conjugated esters and amides react with aryldiazonium salts at room temperature (MeCN) to form the corresponding iminium hydrazone derivatives, which can be thermally cyclized to cinnoline-3-esters and cinnoline-3-amides. In general the intermediate iminium salts derived from the enamine amides cyclize faster than those from the enamine esters. Furthermore, the ease of cyclization depends upon the structure of the base-component of the enamine ester or the amide and the substituent in the aryl moiety of the diazonium salt. The configurational structure of the iminium hydrazones, studied by NMR spectroscopy, has been shown to involve H-bonding of the hydrazonyl N-H with the ester or the amide CO group.