Vinyl-vinyl, aryl-vinyl, and aryl-aryl bond-forming reactions are one of the most significant methods in synthetic organic chemistry, because the structures produced by the reaction are the general moieties found in natural products, biologically active compounds, and electronic organic materials.1 To date, transition metal-catalyzed coupling reactions have been widely used for the formation of these bonds. Thus, the synthetic approaches for the homo-and cross-coupling reactions using an array of transition metals have so far been reported.2 Among them, the original and most broadly used method is the Ullmann reaction, which is homo-coupling reaction between aryl halides mediated by copper.1f,3 However, the stoichiometric amounts of copper reagent, high temperature, and poor substrate scope are the limitations of the reaction. Moreover, although a variety of aryl-aryl bond-forming reactions via intermolecular coupling reaction have been developed, the intramolecular coupling reaction for vinyl-vinyl, aryl-vinyl, and aryl-aryl bond formation is still rare. 4 These results prompted us to investigate the intramolecular coupling reaction.Since the beginning of the past decade, we have engaged in the development of efficient transition metal-catalyzed crosscoupling reactions using organoindium reagents. 5 In the course of our continuing interest in this area, we have recently described Pd-catalyzed intermolecular homo-coupling reactions between aryl and heteroaryl halides. 6 Based on these results, we report herein Pd-catalyzed intramolecular coupling reactions between vinyl bromides, aryl and vinyl halides, and aryl iodides mediated by indium, producing medium-sized carbocycles and heterocycles, particularly seven-and eightmembered ring compounds that have received significant attention due to the ubiquity of their skeletons in many natural products (Scheme 1).An initial attempt to achieve the intramolecular coupling reaction is conducted with bis(vinyl bromide) 1a obtained from ethyl phenylsulfonylacetate and 2,3-dibromo-1-propene. Pd on charcoal is the best catalyst among several catalysts [Pd(PPh 3 ) 4 , Pd 2 dba 3 CHCl 3 , and (π-allyl) 2 PdCl 2 ]. DMF (0.5 M) proved to be the solvent of choice among THF, THF-H 2 O, DMF, DMF-H 2 O, PhCH 3 , and CH 3 CN. The best results were obtained with Pd/C (10 mol%), indium (2.0 equiv), and LiCl (3.0 equiv) in DMF (0.5 M) at 100 C for 3 h under nitrogen atmosphere, producing the cyclized product 2a in 61% yield. Moreover, high dilution conditions were not required despite of intramolecular reaction. Additives such as LiBr, LiI, KBr, and KI failed to afford the coupling product in good yield. Control experiments revealed that no coupling product was observed without indium and Pd/C. The use of stoichiometric amounts of indium accelerated the coupling reaction, and indium (10 mol%) resulted in sluggish reaction. Bis(vinyl bromide) 1a pretreated with indium and lithium chloride in DMF was subjected to Pd/C to produce 2a in low yield, indicating that arylindium reagent was not...
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