Lewis and co-workers have recently disclosed a highly functional-group compatible Rh-catalyzed C-H bond activation for the rapid synthesis of functionalized heterocycles. The method relies on the use of rhodium complexed with (Z)-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which behaves as a chelating ligand, addressing the sometimes slow arylations that occur due to dehydrogenation leading to aryl halide hydrohalogenation or reduction. This ligand is used as the tetrafluoroborate salt, which allows easy handling and storage and, when combined with the rhodium precatalyst, provides a highly robust and efficient catalytic system, in many cases performing arylations that were not possible using traditional catalytic methods. The scope of the reaction was examined and a variety of heterocycles were successfully arylated including benzimidazoles, benzoxazoles, benzothiazoles, as well as bisarylimidazoles, with a variety of functionalized aryl bromides (sulfinyl-, chloro-, acetamide-, hydroxy-, and amino-containing functionalities were suitable coupling partners) (Scheme 3).1

Direct Arylation of Heterocycles

Scheme 3.

Lewis JC, Berman AM, Bergman RG, Ellman JA. 2008. Rh(I)-Catalyzed Arylation of Heterocycles via C?H Bond Activation:  Expanded Scope through Mechanistic Insight. J. Am. Chem. Soc.. 130(8):2493-2500. http://dx.doi.org/10.1021/ja0748985