FULL PAPER DOI: 10.1002/ejoc.201000128 An Efficient Iron-Catalyzed Carbon–Carbon Single-Bond Cleavage via Retro-Claisen Condensation: A Mild and Convenient Approach to Synthesize a Variety of Esters or Ketones Srijit Biswas, [a] Sukhendu Maiti, [a] and Umasish Jana* [a] Keywords: Iron / Nucleophilic addition / Cleavage reactions / Esters / Ketones An efficient iron-salt-catalyzed carbon–carbon bond cleav- age occurring through a retro-Claisen condensation reaction has been developed. The reaction is useful for the synthesis of a variety of esters or ketones under mild conditions. This method works under solvent-free conditions without the need of an inert atmosphere. This protocol is also applicable Introduction Transition-metal-catalyzed reactions are among the most powerful tools in modern organic synthesis. Extensive re- search has been done in the development of palladium-, ruthenium-, rhodium-, iridium-, and even nickel-catalyzed reactions. However, due to the high cost and toxic nature of many of these metal catalysts, there has been a recent surge in the development of organic transformations cata- lyzed by much cheaper and more environmentally friendly metals. In this regard, iron has received a great deal of at- tention as an effective and promising alternative transition metal in the field of catalysis due to its high abundance, low price, and environmentally friendly characteristics. [1] As a consequence, a series of novel iron-catalyzed organic trans- formations have been developed. Since the pioneering re- search work of Tamura and Kochi, [2] a number of reactions including iron-catalyzed oxidation, [3] hydrogenation, [4] hydrosilylation, [5] rearrangement, [6] Michael addition, [7] car- bon–carbon [8–10] and carbon–heteroatom bond-forming re- actions, [11] and oxidative coupling of arynes [12] have been extensively studied. In addition to that, various iron-cata- lyzed cross-coupling reactions including Sonogashira, [13] Heck, [14] Kumada, [15] Negishi, [16] and Suzuki [17] reactions have also been developed. Moreover, iron salts have been successfully employed for the synthesis of various heterocy- clic compounds by us and other groups. [18] More recently, we [19] and others [20] have also discovered novel iron-cata- lyzed activation of alcohols towards various nucleophiles. [a] Department of Chemistry, Jadavpur University, Kolkata 700032, West Bengal, India Fax: +91-33-2414-6584 E-mail: jumasish2004@yahoo.co.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.201000128. Eur. J. Org. Chem. 2010, 2861–2866 © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2861 for the one-pot syntheses of ketones through tandem carbon– carbon bond formation (substitution or Michael) followed by a retro-Claisen reaction. However, for Michael adducts, ring annulation takes place subsequently. Notably, this method is very simple, convenient, high yielding, and only a catalytic (5 to 10 mol-%) amount of Fe(OTf) 3 is needed. Therefore, considering these advantages and the diversity of iron, the discovery of new iron-catalyzed reactions and methodologies is still very much in demand in both acade- mia and industrial research. On the other hand, the catalytic cleavage of a carbon– carbon single bond by transition-metal complexes is a po- tentially useful organic transformation, for which, extensive studies have been done. [21] However, in most of the reac- tions, highly strained compounds such as three- or four- membered carbocycles [22] and compounds with good leav- ing groups [23] or chelating compounds [24] have been demon- strated as substrates. Therefore, the development of new re- actions and reagents for the catalytic cleavage of the car- bon–carbon bond remains a challenging issue. During our recent investigation of iron-salt-mediated direct alkylation of active methylene compounds with benzylic and allylic alcohols, [19d] we noticed that when an aliphatic alcohol was treated with acetylacetone, an ester was produced by direct carbon–carbon bond cleavage through a retro-Claisen condensation type reaction. [25] This observation encouraged us to study systematically the scope of this reaction in organic synthesis. Herein, we wish to re- port our discovery of an efficient, mild, and inexpensive iron(III) trifluoromethanesulfonate mediated carbon–car- bon bond cleavage reaction for the synthesis of esters or ketones from acetylacetone and their derivatives by direct Scheme 1. Iron-salt-catalyzed retro-Claisen condensation reaction.