Arenes carbon-hydrogen bond functionalizations

Copper is underutilized as a catalyst for C-H bond functionalization even though it was the first transition metal shown to promote carbon-hydrogen bond arylation. In 1941, Steinkopf, Leitsmann, and Hofmann showed that Ullmann reaction of 2-iodothiophene produces substantial amounts of tritiophene [88], This reaction necessarily involves one C-H bond arylation step. Subsequently, it has been shown that electron-deficient arenes such as polynitrobenzenes and pentafluorobenzene,... 

On the other hand, the direct arylation of carbanionic species generated from substrates having relatively acidic hydrogens such as active methylene compounds and ketones can occur (mechanism B) [5,6]. Aryl halides are also capable of coupling directly with appropriately functionalized aromatic substrates and five-membered heteroaromatic compounds as formal carbon nucleophiles via cleavage of their unactivated C-H bonds [5,7-9]. The Fujiwra-Moritani reaction, which is the arylation of alkenes with arenes, is also useful for preparing arylalkenes without employing any halides (mechanism D) [10,11]. 

---