Scope and Limitations of the Palladium-Catalyzed Direct 1,2-Diheteroarylation of 1,2-Dihalobenzene Derivatives

Abstract

The reactivity of 1,2-dihalobenzenes in the palladium-catalyzed C-H bond functionalization is more difficult to control than that of 1,3- and 1,4-dihalobenzenes because of a possible Pd 1,4-migration during the second catalytic cycle. With C3-substituted heteroarenes this Pd 1,4-migration is not possible and the reaction allows the synthesis of a wide variety of functionalized 1,2-heteroarylated benzene derivatives in high yields. Conversely, only a few heteroarenes with a free C3-position such as thiazoles, allowed us to prepare the 1,2-heteroarylated benzenes. Despite these limitations, this one pot procedure which employ an easily available catalyst and an inexpensive base provides a very simple method for the preparation of several 1,2-heteroarylated benzenes.

Double C–H bond functionalization for C–C coupling at the β-position of thiophenes using palladium-catalyzed 1,4-migration associated with direct arylation

“…We have recently reported that in the course of the heteroarylation of 1,2-dihalobenzenes by thiophenes, a partial Pd 1,4-migration occurred 12,13 in some cases, leading to a mixture of 1,2-diheteroarylated benzenes and also to aryl-substituted biheteroarenes such as 2′-aryl-2,3′-bithiophenes. 14 This Pd 1,4-migration on thiophene derivatives provides an appealing method for functionalizing the C–H bonds at the β-position of thiophenes which are often more difficult to activate than those at the α-position. 15 In addition, so far, the preparation of 2′-aryl-2,3′-bithiophene derivatives requires multi-step synthesis and the substrate scope is very limited.…”