Nickel Nanoparticles Catalyzed Knoevenagel Condensation of Aromatic Aldehydes with Barbituric Acids and 2-Thiobarbituric
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Nickel Nanoparticles Catalyzed Knoevenagel Condensation of Aromatic Aldehydes with Barbituric Acids and 2-Thiobarbituric Acids Jitender M. Khurana • Kanika Vij
Received: 6 February 2010 / Accepted: 15 May 2010 / Published online: 4 June 2010 Ó Springer Science+Business Media, LLC 2010
Abstract An efficient route for the Knoevenagel condensation of aromatic aldehydes with barbituric acids and 2-thiobarbituric acids in the presence of polyvinyl pyrrolidone (PVP) stabilized Ni nanoparticles in ethylene glycol has been reported. A range of biologically important arylidene barbiturates were obtained in high yields (82–97%) in a very short reaction time. Keywords PVP stabilized nickel nanoparticles Knoevenagel condensation Aromatic aldehydes Barbituric acids Ethylene glycol
1 Introduction The Knoevenagel condensation of aldehydes with active methylene compounds is an important and widely employed method for carbon–carbon bond formation in organic synthesis with numerous applications in the synthesis of fine chemicals, hetero Diels–Alder reaction and in synthesis of carbocyclic as well as heterocyclic compounds of biological significance. Barbituric acids and their derivatives have been widely used as a sedative, hypnotic, anaesthetic, anticonvulsant, antiosteoporosis, as well as antitumor agents [1]. Arylidene barbituric acids as well as their 2-thio analogues are useful as intermediates in synthesis of heterocyclic compounds [1], benzyl barbituric derivatives [2], oxadiazaflavines [3], and unsymmetrical disulphides [4]. Additionally, some of them have been recently studied as non-linear optical materials and dyes J. M. Khurana (&) K. Vij Department of Chemistry, University of Delhi, Delhi 110007, India e-mail: [email protected]
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[5]. Various methods have been reported for the Knoevenagel condensation of carbonyl compounds with barbituric acids or 2-thio barbituric acids like homogeneous systems [6–8], solvent-free grinding using NH2SO3H [9], microwave irradiation [10], infra red promoted [11], ionic liquid mediated condensation [12], various acid and base catalyzed condensation reactions including dry condensation with acidic clay catalysts [13–20]. Recently, Ni supported on SiO2 has been used for the selective catalytic Knoevenagel condensation [21]. However, some of these methods have been associated with shortcomings such as longer reaction times, use of expensive catalysts, formation of undesirable di-substituted product, requirement of excess of solvent, lower yields, etc. Therefore, in view of the importance of barbituric acid derivatives, especially 5-arylidene barbiturates, development of a facile and practically efficient methodology for the target Knoevenagel condensation is desired. Transition-metal nanoparticles have gained tremendous importance in the last two decades as they exhibit interesting electrical, optical, magnetic and chemical properties, especially catalytic properties (owing to their large surface area) which cannot be achieved by their bulk counterparts [22–31]. Metal nano
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