Catalyzed C–C Coupling of Aryl Iodides and Boronic Acids

An efficient La2O3-catalyzed new route for the carbon-carbon bond formation in particular, symmetrical and unsymmetrical biphenyls has been developed, which proceeds through carbon-carbon coupling reaction of aryl iodides with boronic acids. The reaction provided the desired products in moderate-to-good yields with a wide range of functional group tolerance. 1. Introduction The formation of new carbon-carbon bonds is of central importance in organic and medicinal chemistry [1, 2]. The development of new methods for carbon-carbon bond formation is a well-growing area in organic chemistry [3]. In the past decades, tremendous efforts have been devoted into the transition-metal catalyzed cross-coupling reactions [4]. The transition metals have played an important role in organic chemistry and this has led to the development of a large number of transition metal-catalyzed reactions for the formation of C–C and carbon-heteroatom bonds in organic synthesis [5, 6]. In the literature, a variety of nontransition and transition metals like palladium [7–9], copper [10, 11], iron [12], nickel [13, 14], cobalt [15], zinc [16], indium [17], solid supported catalyst [18], and metal nanoparticle [19] have been used for the coupling reactions. In fact palladium-catalyzed Suzuki-type cross-coupling reactions are very well explored and frequently used in organic synthesis and medicinal chemistry [1]. Organoborane and boronic acids have been utilised as arylating agent for the C–C bond formation [7–15]. Metal oxides represent one of the most important and widely used solid catalysts, either as active phases or as supports. The metal oxides are the largest family of catalysts in heterogeneous catalysis due to the acid-base and redox properties [20–23]. The outer electron configuration of the transition and noble group metals made them the most frequently used catalysts [24]. These metal oxides have been proved as efficient catalysts for the coupling reaction. Hell and coworkers reported copper-free Sonogashira reaction of alkynes and aryl halides by using Pd/MgLa mixed oxide [25]. Herein, we have developed a La2O3 catalyzed C–C coupling by using aryl halide and boronic acids. 2. Experimental Section 2.1. General Considerations All the substrates used in this study were purchased from Aldrich and used as received. All the solvents were purchased from Ranchem, India and purified using standard methods. The products are characterized by recording 1H, 13C NMR, and ESI-MS by using Bruker Avance 400？MHz instrument and JEOL JMS GC-mate II instrument. 2.2. Typical Procedure for C–C