Palladium-catalyzed 1,4-migration for the regioselective C–H bond functionalization at C2-position of 3-arylthiophenes

Abstract

The regioselective functionalization of the C–H bond at the C2-position of 3-substituted thiophenes is challenging, as both thienyl α-positions may be reactive, generally affording mixtures of C2-, C5- and C2,C5-(di)functionalized thiophenes. We established that using palladium 1,4-migration allows for the regioselective functionalization of only one of the two α-positions of 3-arylthiophenes. The oxidative addition of the 3-(2-bromoaryl)thiophenes to palladium followed by such palladium migration, regioselectively activates the thienyl C2-α-position. Next, C2-heteroarylated 3-arylthiophene derivatives can be obtained through palladium-catalyzed direct coupling with heteroarenes. The new C–C bond that this reaction generates comes from the functionalization of two C–H bonds. This thienyl heteroarylation method tolerates a variety of heteroarenes and several substituents on the 3-arylthiophene. In addition, an easily available air-stable catalyst and an inexpensive base were employed for this reaction.