Exploratory Studies on the Reaction Between Iodoarenes and Acetylenes: One-pot, Pd-[Bmim][BF 4 ] Catalyzed Preparation o
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Exploratory Studies on the Reaction Between Iodoarenes and Acetylenes: One-pot, Pd-[Bmim][BF4] Catalyzed Preparation of Trianisylethylene Jose´ C. Barros • Andrea L. F. Souza • Joaquim F. M. da Silva • O. A. C. Antunes
Received: 9 April 2010 / Accepted: 8 January 2011 / Published online: 26 January 2011 Ó Springer Science+Business Media, LLC 2011
Abstract The reaction between iodoarenes and acetylenes mediated by palladium was studied, showing selectivity changes based on the nature of the substituent. A new, phosphine-, copper-, and amine-free methodology was developed, in which the synthesis of trianisylethylene from 4-iodoanisole and trimethylsilylacetylene was promoted presumably by an N-heterocyclic-carbene derived from an ionic liquid and a palladium salt, using ethanol as the hydrogen source. Keywords SERM
Sonogashira reaction Hydroarylation
1 Introduction Substituted olefins are valuable building blocks in organic synthesis as they constitute the skeleton of oligoenes and enynes present in natural products [1, 2], which show interesting photochemical properties [3, 4]. In a medicinal context, the triarylyethylene pharmacophore possess biological activities in estrogen-dependent disorders like
This paper is dedicated to the memory of Professor Octavio Antunes and his family.
Electronic supplementary material The online version of this article (doi:10.1007/s10562-011-0549-7) contains supplementary material, which is available to authorized users. J. C. Barros A. L. F. Souza J. F. M. da Silva (&) O. A. C. Antunes Instituto de Quı´mica, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos 149, CT Bloco A, Cidade Universita´ria, Rio de Janeiro, RJ 21941-909, Brazil e-mail: [email protected]
breast cancer, infertility, osteoporosis, CNS, cardiovascular or lipid malfunctions [5, 6]. Compounds of this class like tamoxifen, clomiphene and broparoestrol (Fig. 1) are called Selective Estrogen Receptor Modulators (SERMs). As they are neither estrogen nor hormones, they are considered to be potentially safer than hormone replacement therapy [7], and are now a strategy to prevent osteoporosis and reduce the risk of breast cancer in postmenopausal women [8, 9]. Current approaches to these substituted ethylenes include the hydroarylation reaction mediated by transition metals like copper [10], cobalt [11], iron [12], gold [13, 14], rhodium [15, 16], rhenium [17], platinum [18–20] or palladium [20–27], and metal-free protocols [28]. Our group has been involved in the reaction between haloarenes and acetylenes involving either Sonogashira coupling [29, 30] or tandem Sonogashira coupling-hydroarylation [31] to furnish trisubstituted olefins, and in that case, it was possible to direct the selectivity based on catalyst nature, ligand and solvent properties, also the phosphine-free and ionic liquid promoted reaction were tested (Scheme 1). Here, we wish to disclose an expansion of our methodology using different halides and acetylenes. For this we have subjected alkynes and halides to our optimize
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