Copper-catalyzed cross -coupling reactions: The formation of carbon-carbon and carbon -sulfur bonds
We have developed copper-catalyzed cross-coupling reactions for the formation of carbon-carbon and carbon-sulfur bonds. These newly developed methods demonstrate that the conditions of the traditional Ullmann reaction can be improved. We describe the synthesis of diarylacetylenes through the cross-coupling of aryl iodides and phenylacetylene using [Cu(phen)PPh 3Br] as the catalyst. This method is then utilized for the synthesis of 2-aryl-benzo[b]furans via a copper-catalyzed cross-coupling reaction between aryl acetylenes and 2-iodophenols and a subsequent 5-endo-dig cyclization. The formation of carbon-acetylene bonds is also extended to include vinyl iodides for the purpose of synthesizing 1,3-enynes. Due the lack of a general metal-mediated synthesis of aryl sulfides, we developed a copper-catalyzed cross-coupling reaction between aryl iodides and thiols using a catalytic amount of CuI and 2,9-dimethyl-1,10-phenanthroline as an additive. This method was also extended to include vinyl iodides for the synthesis of vinyl sulfides using [Cu(phen)(PPh3)2]NO3 as the catalyst. All of these methods afford the desired product in good to excellent yields without the use of palladium or expensive/air sensitive additives.