Abstract
The versatile, hitherto unreported pyridine-2,6-bis-(3-oxo-3-propanenitrile) 2 was prepared by the Claisen condensation of pyridine-2,6-dicarboxylic acid ester 1 with acetonitrile in the presence of sodium hydride. Several new pyrazoles, isoxazoles, and pyrazolopyridazine derivatives have been synthesized by the reaction of pyridine-2,6-bis-(3-oxo-3-propanenitrile) 2 with bidentate nucleophilic reagents and hydrazonoyl chloride derivatives.
Highlights
Substituted 3-oxopropanenitriles represent a category of versatile synthetic intermediates. They provide miscellaneous building blocks in the synthesis of several types of heterocyclic ring systems based on a wide range of condensation and cyclization reactions.[1,2,3,4,5,6,7,8,9]
A great deal of interest has been focused on the synthesis of the functionalized pyridine derivatives due to their biological activities.[10,11]
Pyrazoles have important applications in medicinal chemistry. They have emerged as analgesic and anti-inflammatory drugs.[14,15]. In view of these observations and in continuation of our work on the synthesis of heterocyclic systems for biological evaluations,[16,17,18,19] we considered it attractive to synthesize some pyrazoles and isoxazoles incorporated into pyridine moiety at position 2 and 6
Summary
Substituted 3-oxopropanenitriles represent a category of versatile synthetic intermediates. Compound 2 reacted with phenyl hydrazine in ethanol in the presence of a catalytic amount of piperidine, to yield a product which may be formulated as 5 or its isomer 6 (Scheme 2). Structure 5 was considered for a product based on similarity to the well established behavior of acyl and aroyl acetonitrile on the reaction with aryl hydrazines.[25] Structure 5 was further confirmed by the treatment of oxonitriles 2 with phenyl hydrazine at room temperature to give the open structure 4 which undergoes intramolecular cyclization when refluxed in ethanol in the presence of pipredine to afford a compound identical in all respects (TLC, mp, and spectra) with those of compound 5 (Scheme 2).
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