Arylations of Electron-Deficient Heteroarenes

However, for the preparation of compounds with Ar-HetAr or HetAr-HetAr bonds bearing 3-, 4- or 5-substituted electron-deficient heterocyclic moieties, direct arylations using halogenated electron-deficient heteroarenes as electrophiles are usually superior. Selected examples of such couplings are summarized in Table 9.1. 

---

C—H bond arylations of electron-deficient heteroarenes, such as azines, remain highly challenging. An elegant and versatile solution was recently elaborated, however, through a redistribution of electron density in the starting pyridine by chemical modification [77, 78]. It was found that pyridine N-oxides smoothly underwent regioselectively palladium-catalyzed direct arylations with a variety of aryl bromides (Scheme 9.36) [77a]. 

Regioselectivity for direct arylation of electron-deficient heteroarenes ... 

In 2009, Chatani and Tobisu [180] found that the C-H arylation of electron-deficient heteroarenes such as quinolines and pyrazines can be achieved with diarylzinc reagents in the presence of a Ni /PCyj catalyst. In 2010, Zhang... 

---