Formation of methyl 2-arylhydrazono-3-oxobutanoates and 2-arylhydrazono-3-oxobutanenitriles during the coupling reaction of arenediazonium ions with methyl 3-aminocrotonate and 3-aminocrotononitrile

Abstract

Reaction of aryldiazonium salts with methyl 3-aminocrotonate (1) affords high yields of the methyl 2-arylhydrazono-3-oxobutanoates (4); analogous diazonium coupling with 3-aminocrotononitrile (2) gives the 2-arylhydrazono-3-oxobutanenitriles (5). The hydrazones are the product of diazonium coupling at the C2-vinylic carbon, concomitant with hydrolysis of the 3-amino substituent to the 3-oxo derivative; there is no evidence for the formation of a triazene (6), which would be the product of N-coupling. All hydrazones (4a–e and 5a–d) have been fully characterized by IR and 1H and 13C NMR spectroscopy; the NMR spectra of the methyl 2-arylhydrazono-3-oxobutanoates (4) suggest the presence of two isomeric intramolecularly H-bonded forms in solution. Selected compounds were further characterized by elemental analysis and mass spectrometry. A mechanism is proposed for the conversion of 1 or 2 into 4 or 5, and these observations are compared with previously reported observations of diazonium coupling reactions with unsaturated systems. Keywords: hydrazone, diazonium, aminocrotonate, aminocrotononitrile, hydrogen bonding.