%0 Journal Article
%T A Novel Regiospecific Synthesis of 1-Chloro-2-arylcyclohexenes
%A Lokesh Krishnappa
%A HariPrasad Suresh
%J Organic Chemistry International
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/871595
%X An efficient high yielding chemoselective synthesis of eleven novel 1-chloro-2-arylcyclohexenes employing the Suzuki cross coupling of 1-bromo-2-chlorocyclohexene with eleven different aryl boronic acids and Pd(dppf) catalyst is reported. 1. Introduction Cross-coupling reactions of unsaturated carbon centres bearing halogens/triflates with aryl boronic acids catalyzed by palladium metal complexes have become a powerful tool in organic synthesis for the formation of carbon-carbon bonds. One of the important cross-coupling reactions in this genre is the Suzuki reaction [1每4]. These organopalladium complex catalyzed couplings of unsaturated halides with boronic acids/esters have been employed in key steps to form a wide variety of pharmaceuticals and natural products [5每10]. 1,2-Dihalocycloalkenes are precursors to cycloalkynes [11, 12]. However, there are very few reports for the conversion of 1,2-dihalocycloalkenes to substituted 1-halo-2-arylcycloalkenes. One report shows the chemoselective cross coupling of 2-bromo-3-chloronorbornadiene to 2-chloro-3-aryl-norbornadiene [13]. In this regard, the Suzuki coupling reaction of cyclohexenyl bromides with arylboronic acids is still almost unexplored. A recent report shows its importance in the synthesis of polysubstituted phenol derivatives [14]. Our laboratory is involved in the synthesis and reactions of some novel cyclic vinyl silanes. We employ the Wurtz-Fittig coupling reaction of corresponding cyclic vinyl halide with sodium and chlorotrimethylsilane in suitable solvent to prepare the cyclic vinylsilanes. Using the Wurtz-Fittig reaction, we have been able to synthesize a large number of simple and substituted cyclic vinylsilanes [15每19]. The organosilicon compounds are anionic synthons serving as the starting materials in the total synthesis of natural products [20每23]. Cyclic vinyl halides and 1,2-dihalocycloalkenes serve as precursors to the cyclic vinylsilanes. There are several protocols for the preparation of cyclic vinyl halides and 1,2-dihalocycloalkenes [24]. The protocols for 1,2-dihalocycloalkenes normally afford the two halogen atoms symmetrically attached to the carbon-carbon double bond [25, 26]. In comparison to the preparation of symmetrical 1,2-dihalocycloalkenes, there exist very few protocols for the synthesis of unsymmetrical 1,2-dihalocycloakenes especially 1-bromo-2-chlorocycloalkenes [27每31]. We had earlier adopted the addition reaction of bromine chloride to 1-chlorocyclopentene followed by dehydrochlorination for the synthesis of 1-bromo-2-chlorocyclopentene [25]. In this paper,
%U http://www.hindawi.com/journals/oci/2014/871595/