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-AMINO-CROTONONITRILE

Reaction of aryldiazonium salts with methyl 3-aminocrotonate (1) affor ds high yields of the methyl 2-arylhydrazono-3-oxobutanoates (4); anal ogous diazonium coupling with 3-aminocrotononitrile (2) gives the 2-ar ylhydrazono-3-oxobutanenitriles (5). The hydrazones are the product of diazonium coupling at the C2-vinylic carbon, concomitant with hydroly sis of the 3-amino substituent to the 3-oxo derivative; there is no ev idence 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 charact erized by IR and H-1 and C-13 NMR spectroscopy; the NMR spectra of the methyl 2-arylhydrazono-3-oxobutanoates (4) suggest the presence of tw o isomeric intramolecularly H-bonded forms in solution. Selected compo unds were further characterized by elemental analysis and mass spectro metry. A mechanism is proposed for the conversion of 1 or 2 into 4 or 5, and these observations are compared with previously reported observ ations of diazonium coupling reactions with unsaturated systems.