Indian Journal of Chemistry Vol. 53B, August 2014, pp 1122-1127 Ferric nitrate nonahydrate as a mild and efficient catalyst for the synthesis of -enaminones Rajni Khajuria, Ambica, Yeshwinder Saini & Kamal K Kapoor* Department of Chemistry, University of Jammu, Jammu 180 006, India E-mail: k2kapoor@yahoo.com Received 13 August 2013; accepted (revised) 12 June 2014 Ferric nitrate nonahydrate (Fe(NO 3 ) 3 . 9H 2 O) has been found to be an extremely mild and efficient catalyst for the preparation of -enaminones from -dicarbonyl compounds and amines (aliphatic amines, aromatic amines and -amino acid esters). Keywords: Ferric nitrate nonahydrate, -dicarbonyl compounds, amines, -enaminones Enamination of -dicarbonyl compounds forming -enaminones is an important and widely used transformation in organic chemistry 1 . Enaminones are known to possess a variety of medicinal properties 2 including antibacterial, anticonvulsant, antimalarial, antiinflammatory, antitumor, and cardiovascular effects. They serve as important precursors for the synthesis of a variety of heterocycles 3 , -aminoacids and -aminoesters 4 , -aminoalcohols 5 , peptides 6 , alkaloids 7 and pharmaceutical compounds 8 . Moreover, enamine formation is used for the protection of amino acids 9 . Despite of their wide range of synthetic applications and pharmacological activity, the synthesis of -enaminones has received little attention. The most well-known method for the synthesis of -enaminones involves the refluxing of -dicarbonyl compounds with amines in an aromatic solvent with the azeotropic removal of water 10 . Several improved procedures reported for the synthesis of -enaminones include the reaction of amines and -dicarbonyl compounds supported on silica with the microwave irradiation 11 , clay K 10 /ultra-sound 12 , or NaAuCl 4 13 . These compounds have also been prepared by direct condensation of primary amines and -dicarbonyl compounds in water as solvent 14 . Other methodologies involving silver nanoparticles 15 , tungstophosphoric acid 16 , 3-nitrophenylboronic acid 17 , ytterbium triflate 18 , silica chloride 19 , silica ferric hydrogensulfate 20 and dilute hydrochloric acid 21 have also been developed for the enamination of -dicarbonyl compounds. Synthesis of enaminones has also been achieved by coupling thioamides with -diazodicarbonyl compounds 22 . However, most of these methods suffer from one or more of the drawbacks like unsatisfactory yields, long reaction times, lack of general applicability, use of expensive catalysts and tedious experimental procedures. Ferric nitrate nonahydrate has been used as an efficient catalyst in organic transformations 23 . In continuation of our ongoing efforts to the usage of various Lewis acids in organic synthesis 24 , ferric nitrate nonahydrate has been explored for the synthesis of -enaminones as it is non-toxic, easy to handle and low in cost. Results and Discussion A simple, mild and efficient method for the synthesis of -enaminones from amines and -dicarbonyl compounds using ferric nitrate nonahydrate as catalyst has been reported (Scheme I). To optimize the reaction conditions, various Lewis acid catalysts were scanned in order to compare their catalytic activity for the model reaction involving aniline and methyl acetoacetate. It was noticed that the formation of the product enaminone occurred in all the cases with no significant benefit in terms of yield and time (Table I). The result of entry 3 of Table I involving Fe(NO 3 ) 3 . 9H 2 O becomes particularly interesting as it is a non-toxic, inexpensive, efficient, mild and environmentally benign catalyst. To evaluate the versatility of the methodology employing Fe(NO 3 ) 3 . 9H 2 O as catalyst, a range of aliphatic amines, aromatic amines, -amino acid esters and -dicarbonyl compounds were examined and the results are summarized (Table II). All the reactions proceeded well at RT and the products were obtained in good yields (66-92%). The reaction worked smoothly with both activated and weakly activated aromatic amines. However, aromatic amines