Transition-metal-catalyzed direct arylations via C–H bond cleavages
Palladium catalysts allowed for intermolecular direct arylations of heteroarenes with aryl chlorides, tosylates, or mesylates as electrophiles. As an economically attractive alter-native, inexpensive copper catalysts could be employed for regioselective C–H bond aryl-ations of 1,2,3-triazoles. On the contrary, intermolecular C–H bond functionalizations of arenes were accomplished with ruthenium complexes derived from air-stable (heteroatom-substituted) secondary phosphine oxide (HASPO) preligands. Particularly, the use of ruthenium(II) carboxylate complexes enabled broadly applicable direct arylations with inter alia aryl tosylates and phenols, and set the stage for unprecedented intermolecular direct alkylations with unactivated alkyl halides bearing β-hydrogens.