One Pot Access to 2'‐Aryl‐2,3'‐Bithiophenes via Twofold Palladium‐Catalyzed C‐X/C‐H Coupling Associated to a Pd‐1,4‐Migration

International audienceThe reactivity of 1,2-dihalobenzenes in palladium catalyzed polyheteroarylation via C-H bond functionalization was investigated. The first catalytic cycle using thiophene as the heteroarene gives the expected 2-(2-bromophenyl)thiophenes. In the course of the second catalytic cycle, in the presence of heteroarenes having a free C3-position, a partial Pd 1,4-migration occurred giving rise to aryl-substituted biheteroarenes such as 2'-aryl-2,3'-bithiophenes as well as the expected 1,2-di(thiophen-2-yl)benzenes. The best selectivities in favor of the formation of 2'-aryl-2,3'-bithiophenes were obtained with electron-rich 1,2-dihalobenzenes. A wide variety of thiophene derivatives bearing useful functions such as formyl, acetyl, cyclopropylmethanone, 2-methyl-1,3-dioxolane, ester, nitrile or chloro was tolerated allowing to prepare poly-functionalized 2'-aryl-2,3'-bithiophenes. Moreover, this one pot preparation of 2'-aryl-2,3'-bithiophenes employs a low loading of an air stable commercially available palladium source associated to an inexpensive base