General Papers ARKIVOC 2004 (i) 156-162 ISSN 1424-6376 Page 156 © ARKAT USA, Inc Synthesis of squaric acid ester-containing ferrocene derivatives Angélica Aguilar-Aguilar, a Eduardo Peña-Cabrera,* a and Lanny S. Liebeskind b a Facultad de Química. Universidad de Guanajuato. Col. Noria Alta S/N. Guanajuato, GTO. Mexico 36050 b Emory University, Department of Chemistry, 1515 Pierce Drive, Atlanta, Georgia 30322. USA E-mail: eduardop@quijote.ugto.mx (received 12 May 04; accepted 11 Jun 04; published on the web 14 Jun 04) Abstract The synthesis of the first three members of the family of the squarylferrocenes is reported. Their preparation involved both the traditional squaric acid chemistry as well as the Liebeskind-Srögl cross-coupling. Keywords: Ferrocene, squaric acid esters, cyclobutendione, Liebeskind-Srögl cross-coupling Introduction Ever since its discovery fifty years ago, the chemistry of ferrocene has developed dramatically. 1 Its remarkable and versatile properties have allowed its use in a wide variety of applications such as homogeneous asymmetric catalysis, organic synthesis, chemical sensors, molecular electronics, and so on. 2 As part of a program of developing novel ferrocene derivatives to be used as precursors of ligands in homogeneous catalysis, polymers, DNA intercalators, etc., we considered the preparation of ferrocene derivatives that contain a moiety capable of undergoing easy transformation into a variety of functionally useful systems. Squaric acid esters, and the cyclobutendiones prepared from them, have proven to be extremely useful for the synthesis of organometallic, aromatic, heteroaromatic, and non-aromatic polycyclic products. 3 Thus, we envisioned that the cyclobutendione moiety, once attached to ferrocene, would be a suitable starting material for the synthesis of the aforementioned ferrocene derivatives. Our results were first disclosed in a preliminary format in 2001. 4 Zora et al., 5 building on our initial disclosure, recently published chemistry very similar to ours. We therefore more formally describe herein our studies of the synthesis of “squarylferrocenes”.