High-yielding intramolecular direct arylation reactions with aryl chlorides

[reaction: see text] An N-heterocyclic carbene palladium catalyst system is used to promote direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls. An influence of the halide on the palladium precatalyst on catalyst activation has been revealed, as has a beneficial effect of NHC salts that allows the turnover numbers to be increased by simple addition of imidazolium salts to the reaction mixture.     

An efficient silane-promoted nickel-catalyzed amination of aryl and heteroaryl chlorides

A new silane-promoted nickel-catalyzed amination of aryl chlorides with 0.5 mol % of Ni(acac)2, 1 mol % of 3,5,6,8-tetrabromo-1,10-phenanthroline, and polymethylhydrosiloxane was developed. A broad range of aryl and heteroaryl chlorides can be coupled with secondary amines and anilines to give the desired (het)arylamines in good to excellent yields. The reaction is sensitive to the nature and amount of the silane promoter.     

Efficient palladium-catalyzed amination of aryl chlorides using di(dicyclohexylamino)phenylphosphine as a PN2 ligand

The palladium-catalyzed amination of a variety of aryl chlorides has been accomplished by using di(dicyclohexylamino)phenylphosphine (1) as a bulky electron-rich monoaryl phosphine ligand. The optimized condition for the palladium-catalyzed amination of aryl chloride is the followings: aniline (3.0 mmol, 1.0 equiv), chlorobenzene (3.15 mmol, 1.05 equiv), ligand 1 (1 mol %, 0.03 mmol), KO^tBu (4.5 mmol, 1.5 equiv), Pd₂(dba)₃ (1 mol %, 0.03 mmol), and toluene as solvent at reflux temperature. We report on couplings of various amines or chloroamines with chlorobenzenes and heteroaryl chloride.     

Solvent-free mechanochemical Buchwald-Hartwig amination of aryl chlorides without inert gas protection

A solvent-free Buchwald-Hartwig amination had been developed under high-speed ball-milling conditions, which afforded the desired products with moderate to high yields. The addition of sodium sulfate was found to be crucial for improving both the performance and the reproducibility. Comparative solvent-free stirring experiments implicated the importance of mechanical interaction for the transformation, and the inert gas was proved to be unnecessary for this amination.     

A recyclable Cu/Al-HT catalyst for amination of aryl chlorides

A simple Cu/Al-HT catalyzed amination of aryl chlorides with primary and secondary aromatic amines has been developed. This ligand-free heterogeneous Cu/Al-HT catalyst, in conjunction with base, also efficiently works for the amination of aryl chlorides with cycloalkylamines. This method tolerates a variety of functional groups and does not require an expensive additive.     

Triazole-based monophosphines for Suzuki-Miyaura coupling and amination reactions of aryl chlorides

[reaction: see text] A new class of triazole-based monophosphine 1 (ClickPhos) has been prepared via efficient 1,3-dipolar cycloadditions of readily available azides and acetylenes. Palladium complexes derived from these ligands provide highly active catalysts for Suzuki-Miyaura coupling and amination reactions of aryl chlorides.     

New ligands for a general palladium-catalyzed amination of aryl and heteroaryl chlorides

The synthesis and application of monodentate N-substituted heteroarylphosphines is described. In general, the ligands are conveniently prepared by selective metallation at the 2-position of the respective N-substituted heterocycle (pyrrole, indole) by using n-butyllithium/tetramethylethylenediamine (TMEDA) followed by quenching with dialkyl- or diarylchlorophosphines. Of the different ligands prepared, the new dialkyl-2-(N-arylindolyl)phosphines (cataCXium P) perform excellently in the palladium-catalyzed amination of aryl and heteroaryl chlorides. Coupling of both activated and deactivated chloroarenes proceeds under mild conditions (room temperature to 60 degrees C). By using optimized conditions remarkable catalyst productivity (total turnover number, TON, up to 8000) and activity (turnover frequency, TOF=14000 h(-1) at 75% conversion) are observed.     

Novel CuI/tributyl phosphine catalyst system for amination of aryl chlorides

A simple and efficient methodology for the synthesis of triarylamines from aryl chlorides in a single step has been demonstrated using a novel CuI/tributyl phosphine catalyst system with high activity and selectivity (80-87% yield).     

Efficient palladium-catalyzed N-arylation of a sulfoximine with aryl chlorides

The efficient N-arylation of a sulfoximine with aryl chlorides was developed by using Pd(2)(dba)(3) as a catalyst and various ligands. The reactions using RuPhos as a ligand afforded the coupled products in fair to excellent yields.     

Aqueous hydroxide as a base for palladium-catalyzed amination of aryl chlorides and bromides

The amination of aryl halides in the presence of inexpensive and air-stable alkali metal hydroxide bases and Pd[P(t-Bu)3]2 as catalyst gave arylamines in high yields. The reactions were conducted with a catalytic amount of cetyltrimethylammonium bromide as phase-transfer agent and either aqueous hydroxide or solid hydroxide in the presence of water. This combination of alkali metal hydroxide base, H2O, and the ammonium salt performed as well as NaO-t-Bu in the amination of p-chlorotoluene with dibutylamine. Hydroxide base was suitable for reactions of a wide range of aryl chlorides and bromides with aliphatic and aromatic amines. Some functional groups that were intolerant of tert-butoxide base, such as esters, enolizable ketones, nitriles, and nitro groups, were tolerated by the combination of hydroxide base, H2O, and cetyltrimethylammonium bromide in toluene solvent.     

Efficient catalyst for the Suzuki-Miyaura coupling of potassium aryl trifluoroborates with aryl chlorides

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of aryl- and heteroaryl chlorides with potassium aryl- and heteroaryltrifluoroborates have been accomplished with the supporting ligand S-Phos in good to excellent yield. Hindered biaryls and substrates containing a variety of functional groups can be prepared. Suzuki-Miyaura couplings of a 3-pyridyl boron-based nucleophile with aryl- and heteroaryl chlorides proceed in good to very good yield. [reaction: see text]     

Synthesis of 1-aryl-1H-indazoles via palladium-catalyzed intramolecular amination of aryl halides

Palladium-catalyzed cyclization of arylhydrazones of 2-bromoaldehydes and 2-bromoacetophenones to give 1-aryl-1H-indazoles has been studied in detail. The cyclization of arylhydrazone of 2-bromobenzaldehydes can be performed with good to high yields using Pd(dba)2 and chelating phosphines, of which the most effective are rac-BINAP, DPEphos, and dppf, in the presence of Cs2CO3 or K3PO4 as a base. Electron-rich, bulky ligands commonly employed for intermolecular amination such as PtBu3 and o-PhC6H4PtBu2 were shown to be ineffective for cyclization and to lead instead to extensive oligomerization and tarring. The method developed is applicable for preparation of a wide scope of indazoles bearing electron-donating or electron-withdrawing substituents, among them, unprotected carboxyl, as well as various indazole heteroanalogues. The cyclization of arylhydrazones of less reactive halides such as 2-chlorobenzaldehyde, as well as 2-bromoacetophenone and bromotetralone, has been achieved. The purity of the starting hydrazone has been shown to be a critical parameter, as various impurities inhibit the cyclization.     

An air and thermally stable one- component catalyst for the amination of aryl chlorides

[reaction: see text] In this paper we report a new, highly efficient palladacyclic precatalyst that is air, moisture, and thermally stable and obviates the need to employ a glovebox. We have developed a convenient one-component precatalyst for the amination of aryl chlorides that overcomes many of the limitations of those previously described.     

Carbene adduct of cyclopalladated ferrocenylimine as an efficient catalyst for the amination of aryl chlorides

A novel air- and moisture-stable carbene adduct of cyclopalladated ferrocenylimine has been synthesized and characterized. The structure of this compound was determined by X-ray crystal structure analysis. This adduct has been applied as an efficient catalyst for the amination of aryl chlorides.     

Unusual nickel-mediated C-S cleavage of alkyl and aryl sulfoxides

The first examples of transition metal mediated C-S cleavage of sulfoxides containing sp2- and sp3-hybridized carbon bonds attached to the sulfur atom and the first example of a structurally characterized complex featuring an oxygen-bound sulfinyl ligand are presented.     

Bulky alkylphosphines with neopentyl substituents as ligands in the amination of aryl bromides and chlorides

Di(tert-butyl)neopentylphosphine (DTBNpP) in combination with palladium sources provided catalysts with comparable or better activity for the Hartwig-Buchwald amination of aryl bromides than tri(tert-butyl)phosphine (TTBP) under mild conditions. DTBNpP also provided effective catalysts for amination reactions of aryl chlorides at elevated temperatures. Further replacement of tert-butyl groups with neopentyl substituents resulted in less effective ligands for amination reactions. Computationally derived cone angles showed that replacement of a tert-butyl group with a neopentyl group significantly increased the cone angle of the phosphine. The larger cone angle of DTBNpP than TTBP appears to correlate with the higher activity of catalysts derived from DTBNpP in the amination of aryl bromides. TTBP is a stronger electron donor than DTBNpP, which may explain the higher activity for TTBP-derived catalysts toward aryl chlorides.