Bis(l-iodo)bis(()-sparteine)dicopper(I) catalyzed Sonogashira-type reaction under palladium and phosphine-free conditions S. Priyadarshini a , P. J. Amal Joseph a , P. Srinivas a , H. Maheswaran a , M. Lakshmi Kantam a,⇑ , Suresh Bhargava b a RMIT-IICT Research Centre, I & PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India b Advanced Materials & Industrial Chemistry Group, School of Applied Sciences, RMIT University, Melbourne, Australia article info Article history: Received 23 November 2010 Revised 19 January 2011 Accepted 26 January 2011 Available online 3 February 2011 Keywords: Sonogashira reactions Copper catalyst Aryl chlorides Sparteine Cross coupling abstract An efficient and inexpensive protocol for the Sonogashira-type cross coupling reactions of phenylacetyl- enes with a variety of haloarenes including activated aryl chlorides employing the structurally well-char- acterized bis(l-iodo)bis(()-sparteine)dicopper(I) catalyst is described. Ó 2011 Elsevier Ltd. All rights reserved. Aryl alkynes are important intermediates in pharmaceutical chemistry, natural products, and material science. 1–3 These com- pounds are often synthesized by the Sonogashira cross coupling reaction of terminal alkynes with aryl halides, employing palla- dium salts in conjunction with copper(I) iodide and phosphine li- gands as catalytic systems. 3–5 The use of expensive palladium phosphine complexes with copper(I) iodide as co-catalyst, made palladium catalysts less useful, in particular, for industrial scale reactions. Therefore, it is highly attractive to perform such reac- tions under palladium and phosphine-free conditions. Recently, copper-catalyzed Sonogashira-type reaction of alkynes with aryl halides 6-16 has gained much attention owing to the lower toxicity and cost of copper salts. A number of phosphine and non-phos- phine ligands, such as triphenylphosphine, 6 1,10-phenanthroline, 7 ethylenediamine, 7c N,N-dimethylglycine, 8 1,4-diazabicyclo[2.2.2]- octane (DABCO), 9 1,1’-binaphthyl-2,2’-diamine (BINAM) and its derivatives, 10 1,1’-binaphthyl-2,2’-diol (rac-BINOL), 11 b-dike- tones, 12 pyrimidines, 13 salicylic acid, 14 8-hydroxyquinoline 15 and N,N 0 -dimethylethylenediamine (DMEDA) 16 have been examined for copper-catalyzed Sonogashira-type coupling reactions. Most of these protocols employ either high loading of copper salts/ ligands or they lack substrate generality. Moreover, it remains a challenging task to activate less reactive aryl halides, such as deactivated aryl bromides and chlorides for Sonogashira cross cou- pling reactions under palladium and phosphine-free conditions. Generally the copper-catalyzed Sonogashira reactions are car- ried out using a catalyst generated in situ by combining the Cu source with the excess free ligands. Although these practices are quite useful in both small-scale and process chemistry operations, they suffer from many drawbacks; for example, an excess of ligand often inhibits the activity of the catalytic system and is not cost efficient, and the generation of the active species from the ligand and Cu source may also require an induction period or result in undesired side products due to the formation of metal complexes with different reactivity. Therefore, there is an increasing interest in using pre-formed copper complexes of different ligands as precatalysts. Our group has recently shown that the use of the pre-formed dimeric copper complex [Cu 2 I 2 (()-sparteine) 2 ] containing a Cu 2 (l-I) 2 core coordinated by sterically hindered and poor r-donor ligands, such as ()-sparteine, in conjunction with CuI, 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.01.119 ⇑ Corresponding author. Fax: +91 40 27193510. E-mail address: mlakshmi@iict.res.in (M.L. Kantam). N N H H Cu N N H H Cu I I N N H H Cu N N H H Cu Cl Cl 1 2 Figure 1. Bis(l-halo)bis(()-sparteine)dicopper(I) complexes. Tetrahedron Letters 52 (2011) 1615–1618 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet