Site-Specific Phenylation of Pyridine Catalyzed by Phosphido-Bridged Ruthenium Dimer Complexes: A Prototype for C−H Arylation of Electron-Deficient Heteroarenes

A solution to the 2-pyridyl organometallic cross-coupling problem: regioselective catalytic direct arylation of pyridine N-oxides

Direct arylation reactions of pyridine N-oxides occur in excellent yield with complete selectivity for the 2-position with a wide range of aryl bromides. This reactivity permits the use of inexpensive, commercially available, and bench-stable pyridine N-oxides as replacements for problematic 2-metallapyridines in palladium-catalyzed cross-coupling reactions.

Scope and mechanistic study of the ruthenium-catalyzed ortho-C-H bond activation and cyclization reactions of arylamines with terminal alkynes

The cationic ruthenium hydride complex [(PCy(3))(2)(CO)(CH(3)CN)(2)RuH](+)BF(4)(-) was found to be a highly effective catalyst for the C-H bond activation reaction of arylamines and terminal alkynes. The regioselective catalytic synthesis of substituted quinoline and quinoxaline derivatives was achieved from the ortho-C-H bond activation reaction of arylamines and terminal alkynes by using the catalyst Ru(3)(CO)(12)/HBF(4).OEt(2). The normal isotope effect (k(CH)/k(CD) = 2.5) was observed for the reaction of C(6)H(5)NH(2) and C(6)D(5)NH(2) with propyne. A highly negative Hammett value (rho = -4.4) was obtained from the correlation of the relative rates from a series of meta-substituted anilines, m-XC(6)H(4)NH(2), with sigma(p) in the presence of Ru(3)(CO)(12)/HBF(4).OEt(2) (3 mol % Ru, 1:3 molar ratio). The deuterium labeling studies from the reactions of both indoline and acyclic arylamines with DCCPh showed that the alkyne C-H bond activation step is reversible. The crossover experiment from the reaction of 1-(2-amino-1-phenyl)pyrrole with DCCPh and HCCC(6)H(4)-p-OMe led to preferential deuterium incorporation to the phenyl-substituted quinoline product. A mechanism involving rate-determining ortho-C-H bond activation and intramolecular C-N bond formation steps via an unsaturated cationic ruthenium acetylide complex has been proposed.

Highly Regioselective Arylation of sp3 C−H Bonds Catalyzed by Palladium Acetate

A new palladium-catalyzed arylation process based on C-H activation has been developed. The utilization of pyridine-containing directing groups allows the beta-arylation of carboxylic acid derivatives and gamma-arylation of amine derivatives. Both primary and secondary sp3 C-H bonds, as well as sp2 C-H bonds, are reactive.

Phosphine Oxides as Preligands in Ruthenium-Catalyzed Arylations via C−H Bond Functionalization Using Aryl Chlorides

[reaction: see text] The use of air-stable, electron-rich phosphine oxides as preligands allows for unprecedented general ruthenium-catalyzed arylation reactions of pyridines and imines through C-H-bond activation using aryl chlorides. The catalytic system derived from a sterically hindered adamantyl-substituted phosphine oxide proves highly efficient and tolerates a number of important functional groups.