Rhodium-catalyzed diarylation of oxalates using arylboron compounds

Dialkyl oxalates undergo selective diarylation on one of their carbonyl carbons upon treatment with arylboron reagents in the presence of a rhodium catalyst to give the corresponding alpha-hydroxydiarylacetates. Under similar conditions, the arylation of benzoylformate and benzil also proceeds efficiently.     

Rhodium-catalyzed regioselective arylation of phenylazoles and related compounds with arylboron reagents via C-H bond cleavage

The rhodium-catalyzed direct ortho-arylation reactions of phenylazoles using arylboron reagents such as tetraarylborates were examined. Ethyl chloroacetate and potassium fluoride were found to effectively act as a hydrogen acceptor and a promoter, respectively, to afford selective formation of the corresponding mono- or diarylated products with good yields. In addition, azobenzene as well as 2-phenylpyridine also underwent the direct arylation under similar conditions.     

Rhodium-catalyzed silylation of ortho-functionalized aryl halides with hydrosilanes

The silylation of ortho-functionalized aryl iodide with trialkylsilanes in the presence of RhCl(CO)(PPh₃)₂ or [Rh(cod)₂]BF₄ and K₃PO₄ provides the corresponding arylalkylsilane in good to high yield. This catalytic system showed a dramatically different activity when Pd(t-Bu₃P)₂ was used as a catalyst.     

Palladium-catalyzed direct arylation of nitro-substituted aromatics with aryl halides

Direct arylation reactions of nitrobenzenes and aryl halides occur in good yield and high ortho regioselectivity. These reactions can be performed on gram scale with as few as 3 equiv of the nitro arene relative to the aryl halide. The synthetic utility of this method is demonstrated via rapid synthesis of a Boscalid intermediate.     

Rhodium-catalyzed addition of arylboron compounds to nitriles, ketones, and imines

The rhodium-catalyzed addition reactions of sodium tetraphenylborate and arylboronic acids to nitriles, ketones, and imines were examined. The reaction of nitriles could be carried out efficiently in the presence of a catalyst system of [RhCl(cod)]₂-dppp and H₂O to give the corresponding monoarylated products selectively. Although unactivated ketones and imines are known to be poor electrophiles for rhodium-catalyzed arylation, the phenylation of them with use of sodium tetraphenylborate proceeded smoothly in the presence of [RhCl(cod)]₂ and Rh(acac)(cod) as catalysts, respectively. The addition of NH₄Cl was found to be crucial to effectively conduct the reaction of ketones and imines.     

Palladium-tetraphosphine complex: an efficient catalyst for the coupling of aryl halides with alkynes

The cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)-cyclopentane-[PdCl(eta3-C3H5)]2 system catalyses the coupling of aryl halides with alkynes with very high ratios of substrates-catalyst in good yields; a turnover number of 2600000 can be obtained for the reaction of 4-trifluoromethylbromobenzene with phenylacetylene in the presence of this catalyst.     

CuI/L-proline-catalyzed coupling reactions of aryl halides with activated methylene compounds

[reaction: see text] The arylation of ethyl acetoacetate, ethyl benzoyl acetate, and diethyl malonate under the catalysis of CuI/L-proline in DMSO proceeds smoothly at 40-50 degrees C in the presence of Cs2CO3 to provide the 2-aryl-1,3-dicarbonyl compounds in good yields. Both aryl iodides and aryl bromides are compatible with these reaction conditions.     

Palladium-catalyzed benzylic direct arylation of benzyl sulfones with aryl halides

An effective palladium catalyst system for the direct arylation of benzyl sulfones with aryl halides has been developed. The catalytic reaction provides a facile route to diarylmethyl sulfones. The products can be transformed further via desulfonylative functionalization mediated by aluminum compounds.     

A general and efficient CuI/BtH catalyzed coupling of aryl halides with thiols

We report an exceptionally mild, general and efficient copper catalyzed cross coupling reaction of aryl bromides and thiols using 0.5 mol % CuI and 1 mol % benzotriazole. Experimental simplicity, generality, functional group tolerance and low cost of the catalyst are advantages of the protocol.     

Direct arylation of oxazole and benzoxazole with aryl or heteroaryl halides using a palladium-diphosphine catalyst

Through the use of PdCl(dppb)(C₃H₅) as a catalyst, a range of aryl bromides and chlorides undergoes coupling via C-H bond activation/functionalization reaction with oxazole or benzoxazole in good yields. This air-stable catalyst can be used at low loadings with several substrates. Surprisingly, better results in terms of substrate/catalyst ratio were obtained in several cases using electron-excessive aryl bromides than with the electron-deficient ones. This seems to be mainly due to the relatively low thermal stability of some of the 2-arylbenzoxazoles formed with electron-deficient aryl halides. With these substrates, in order to obtain higher yields of product, the reactions had to be performed at a lower temperature (100-120 °C) using a larger amount of catalyst. On the other hand, in the presence of the most stable products, the reactions were performed at 150 °C using as little as 0.2 mol% catalyst. Arylation of benzoxazole with heteroaryl bromides also gave the coupling products in moderate to high yields using 0.2-5 mol% catalyst. With this catalyst, electron-deficient aryl chloride such as 4-chlorobenzonitrile, 4-chloroacetophenone or 2-chloronitrobenzene have also been used successfully.     

Palladium-catalyzed direct arylation of aryl(azaaryl)methanes with aryl halides providing triarylmethanes

Direct arylation of aryl(azaaryl)methanes with aryl halides takes place at the benzylic position in the presence of a hydroxide base under palladium catalysis to yield triarylmethanes.     

New efficient preparation of arylzinc compounds from aryl halides using cobalt catalysis and sacrificial anode process

Electroreduction of aryl-chlorides or -bromides in an electrochemical cell fitted with a sacrificial zinc anode and in the presence of cobalt halide associated with pyridine as ligand in DMF or acetonitrile as solvent affords the corresponding organozinc species in good yields.     

Free porphyrin catalyzed direct C-H arylation of benzene with aryl halides

A general procedure for free porphyrin catalyzed direct C-H arylation of benzene was demonstrated. This air tolerant, transition-metal-free process provides a promising system for cheap and efficient synthesis of biaryls in a user-friendly approach.     

The development of efficient catalysts for palladium-catalyzed coupling reactions of aryl halides

In the mid 1990s, we started a program on the development of more efficient palladium catalysts for the C-C and C-N coupling reactions of aryl halides, especially aryl chlorides. In this contribution, our investigations on new catalyst systems and their application in organic synthesis are summarized.     

A highly efficient catalyst for Suzuki coupling of aryl halides and bromoarylphosphine oxides

The biphenyl-based phosphine, P(o-C₆H₄C₆H₄Me)Ph₂, is a moderately bulky and electron-rich phosphine, which has been successfully applied to the palladium catalyzed Suzuki coupling of activated and deactivated aryl halides as well as bromoarylphosphines and bromoarylphosphine oxides, with low catalyst loading and good to excellent conversions and turnovers.     

Synthesis of diaryl ethers through the copper-catalyzed arylation of phenols with aryl halides using microwave heating

The copper-catalyzed arylation of phenols with a variety of aryl halides using microwave heating is described.     

C-H arylation of unactivated arenes with aryl halides catalyzed by cobalt porphyrin

A general procedure for cobalt-catalyzed direct C-H arylation of unactivated arenes has been discovered. This method employs aryl halides as the direct coupling partners with arenes without using any Grignard-type reagents. This catalysis opens a new methodology for the preparation of symmetrical as well as unsymmetrical biaryls in a user-friendly approach.     

Pd-mBDPP-catalyzed regioselective internal arylation of electron-rich olefins by aryl halides

meso-2,4-Bis(diphenylphosphino)pentane (mBDPP) has proved to be an effective regiocontrolling ligand for palladium-catalyzed internal arylation by aryl bromides of electron-rich olefins in a common solvent DMSO with no need for any halide scavengers. The arylation of the benchmark electron-rich olefin butyl vinyl ether took place smoothly to afford exclusively alpha-arylated product with high isolated yields. The better performance of mBDPP, compared with that of the commonly used DPPP [1,3-bis(diphenylphosphino)propane], highlights the important but subtle effect of ligand on the regioselectivity of the Heck arylation reactions.     

Rhodium-catalyzed reductive coupling of disulfides and diselenides with alkyl halides, using hydrogen as a reducing agent

[reaction: see text] We have established that RhCl(PPh3)3 catalyzes a reductive coupling of disulfides and diselenides with alkyl halides in the presence of triethylamine using hydrogen as a reducing agent. This reaction serves as a convenient new method to produce unsymmetrical sulfides and selenides from disulfides and diselenides instead of unstable and odoriferous thiols and selenols.