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-arninocrotonate (I) 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 3-0x0 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-6) have been fully characterized by IR and 'H and I3c 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.Key words: hydrazone, diazonium, aminocrotonate, aminocrotononitrile, hydrogen bonding.R6sum6 : La rtaction des sels aryldiazoniums avec le 3-aminocrotonate de mtthyle (1) conduit avec d'excellents rendements aux 2-arylhydrazono-3-oxobutanoates de mtthyle (4); des couplages analogues de diazoiques avec le 3-aminocrotonitrile (2) donne les 2-arylhydrazono-3-oxobutanenitriles (5). Les hydrazones sont les produits du couplage des diazoiques au niveau du carbone vinylique C2, suivi de I'hydrolyse du substituant 3-amino qui conduit au dtrivt 3-0x0; il n'y a pas de preuve de la formation d'un triazkne (6) qui pourrait &tre le produit du couplage avec l'azote. On a caracttrist complktement toutes les hydrazones (4a-e et 50-6) par la spectroscopie IR et de RMN du 'H et du 13c. Les spectres de RMN des 2-arylhydrazono-3-oxobutanoates de mtthyle (4) suggkrent la prksence de deux formes isomkres en solution lites par des liaisons hydrogenes intramoltculaires. On a de plus caracttrist les composts choisis par l'analyse tltmentaire et par la spectromttrie de masse. On propose un mkcanisme pour la transformation du compost 1 ou 2 en compost 4 ou 5 et on a compark ces observations avec les observations rapporttes anttrieurement sur le couplage des diazoiques avec les systkmes insaturts.

The effect of ortho and para substituents on the formation of the E and Z isomers of the arylhydrazones obtained from diazonium coupling with methyl 3-aminocrotonate and 3-aminocrotononitrile

“…Reaction of the para-substituted arenediazonium ion (7) with 3-aminocrotononitrile (8 , Y = CN) proceeds directly through the pathway -+ 9 -+ 10 -+ 11 + 1 2 to give a single product, the Z-2-arylhydrazono-3-oxobutanenitrile (1). The formation of a single product is determined by two factors: (i) the favourable entropy factor of the intramolecular process, path (a), over the intermolecular reaction, path (b); and (ii) the stability of the hydrogen-bonded product (12 = 1) over the non-hydrogen-bonded product 14.…”

“…General procedure These compounds were prepared by the general procedure described previously (1). This procedure was successful in the preparation of the 2-(3'-pyridy1)-hydrazono-3-oxobutanenitrile (5) when 3-aminopyridine was used as the arylamine.…”

Synthesis and Tautomeric Structure of 3,7-bis(arylazo)-2,6-dimethyl-1H-imidazo[1,2-b]pyrazoles

“…The physical constants of the products 2a-e were identical to those previously reported. [18][19][20] Synthesis of 4-arylazo-5-amino-3-methylpyrazoles (3); general procedure A mixture of hydrazine hydrate and the appropriate compound 2 (0.01 mole) in absolute ethanol (10 mL) was refluxed for 9 h then the solvent was evaporated to half its volume and the mixture was left to cool. The solid precipitate that formed was filtered off and crystallised from the appropriate solvent to give the respective pyrazole derivative 3.…”

Interplay of hydrogen bonding and other molecular interactions in determining the crystal packing of a series of anti-β-ketoarylhydrazones

“…PARST ( Nardelli, 1983Nardelli, , 1995, SHELXL97 (Sheldrick, 1997) syntheses have been reported elsewhere (Brown et al, 1995;Jollimore et al, 1996). Compounds (a1), (a2) and (a5) were recrystallized from a mixture of ethyl acetate and acetonitrile; (a3) and (a6) from ethyl acetate; (a4) from ethanol.…”