Palladium-catalyzed Amination Research Articles

Palladium-Catalyzed Amination of Aryl Halides with Aqueous Ammonia and Hydroxide Base Enabled by Ligand Development.

The conversion of aryl halides to primary arylamines with a convenient and inexpensive source of ammonia has been a long-standing synthetic challenge. Aqueous ammonia would be the most convenient and least expensive form of ammonia, but such a palladium-catalyzed amination reaction with a high concentration of water faces challenges concerning catalyst stability and competing hydroxylation, and palladium-catalyzed reactions with this practical reagent are rare. Further, most reactions with ammonia to form primary amines are conducted with tert-butoxide base, but reactions with ammonium hydroxide would contain hydroxide as base. Thus, ammonia surrogates, ammonia in organic solvents, and ammonium salts have been used under anhydrous conditions instead with varying levels of selectivity for the primary amine. We report the palladium-catalyzed amination of aryl and heteroaryl chlorides and bromides with aqueous ammonia and a hydroxide base to form the primary arylamine with high selectivity. The palladium catalyst containing a new dialkyl biheteroaryl phosphine ligand (KPhos) suppresses both the formation of aryl alcohol and diarylamine side products. Mechanistic studies with a soluble hydroxide base revealed turnover-limiting reductive elimination of the arylamine and an equilibrium between arylpalladium amido and hydroxo complexes prior to the turnover-limiting step.

Pd-Catalyzed Asymmetric Amination of Enamines: Expedient Synthesis of Structurally Diverse N–C Atropisomers

The transition-metal-catalyzed cross-coupling of enamines is an attractive method for producing compounds with an N–C chiral axis; however, it faces considerable challenges that remain unresolved. Herein, a palladium-catalyzed amination method was developed to construct structurally diverse five–six biaryl and six–six nonbiaryl N–C atropisomers. The reaction mechanism was explained using density functional theory calculations, which showed that the mechanism involved the Curtin–Hammett control. N–C rotation occurred along the reaction coordinate until an enantio-determining three-centered reductive elimination transition structure established the stereochemistry. The developed method is highly attractive because of its broad substrate scope, high stereoselectivity, simple catalytic system, good functional group tolerance, and dynamic kinetic resolution.

Synthesis of 2,5-difunctionalized pyridines via sequential chemoselective amination and Suzuki–Miyaura reactions

Pyridine derivatives are important building blocks in pharmaceutical and materials chemistry. Synthesis of 2-amino-5-(het)arylpyridine derivatives was explored via sequential chemoselective palladium-catalyzed amination and Suzuki–Miyaura cross-coupling reaction. 5-Bromo-2-tosyloxypyridine as a starting material, a new carbon–nitrogen bond was successfully formed chemoselectively on bromide over OTs group, followed by Suzuki–Miyaura couplings with various boronic acids to provide the desired 2-amino-5-(het)arylpyridines in moderate to excellent yields. Using this protocol, a valuable class of pyridine derivatives to be biologically active can be synthesized.

Palladium-Catalyzed Amination for the Synthesis of Macrocycles and Polymacrocycles: Contribution of Professor I.P. Beletskaya

Palladium-Catalyzed Amination for the Synthesis of Macrocycles and Polymacrocycles: Contribution of Professor I.P. Beletskaya

(E)-β-Trifluoromethyl vinylsulfones as antitumor agents: Synthesis and biological evaluations

A three-component reaction of phenylactylene, trifluoromethyl thianthrenium triflate (TT-CF3+OTf−) and sodium sulfinates under extremely mild conditions is developed, leading to various trifluoromethyl-substituted vinyl sulfones in moderate to good yields with excellent stereoselectivity. Additionally, elaboration of trifluoromethyl-substituted vinyl sulfone by palladium-catalyzed amination is performed. These trifluoromethyl-substituted vinyl sulfones are further evaluated for several assays against different tumor cells and the antitumor mechanism in cytotoxic autophagy induced by PI3K/Akt/mTOR signal is investigated.

Palladium-Catalyzed Reductive Amination in an Oscillatory Plug-Flow Reactor

Palladium-Catalyzed Reductive Amination in an Oscillatory Plug-Flow Reactor

Buchwald-Hartwig Amination of Aryl Halides with Heterocyclic Amines in the Synthesis of Highly Fluorescent Benzodifuran-Based Star-Shaped Organic Semiconductors.

The study of palladium-catalyzed amination of bromobenzene with aromatic and heterocyclic amines, widely used in the synthesis of organic semiconductors, was performed. The best conditions for the coupling of aryl bromides with carbazole, diphenylamine, phenoxazine, phenothiazine, 9,9-dimethyl-9,10-dihydroacridine, and their derivatives have been developed. Based on the results, nine new star-shaped organic semiconductors, exhibiting up to 100% fluorescent quantum yield in the 400–550 nm range, have been synthesized in good yields. The TDDFT calculations of the absorption spectra revealed a good correlation with experimental results and slight solvatochromic effects with a change in the polarity of the solvent.

Metal-catalyzed reactions for the C(sp2)–N bond formation: achievements of recent years

The review deals with the main catalytic methods for the C(sp2)–N bond formation, including Buchwald–Hartwig palladium-catalyzed amination of aryl and heteroaryl halides, renaissance of the Ullmann chemistry, i.e., the application of catalysis by copper complexes to form the carbon–nitrogen bond, and Chan–Lam reactions of (hetero)arylboronic acids with amines. Also, oxidative amination with C–H activation, which has been booming during the last decade, is addressed. Particular attention is paid to achievements in the application of heterogenized catalysts.The bibliography includes 350 references.

A terphenyl phosphine as a highly efficient ligand for palladium-catalysed amination of aryl halides with 1° anilines

A terphenyl phosphine ligand (2,6-bis(2,4,6-triisopropylphenyl)phenyl-dicyclohexylphosphine, TXPhos) and its supported palladium complex [(TXPhos)(allyl)PdCl] have been developed and the catalyst system is highly efficient in amination of aryl halides with 1° anilines, especially effective for densely functionalized substrates including both partners possessing ortho-ester, acetyl, nitrile and nitro groups. With the TXPhos-supported catalyst system, many partner combinations have been unprecedentedly realized and the base scope has been even extended to KOAc, which is even the best choice in the amination of 2-nitrochlorobenzene.

Ylide-Substituted Phosphines with a Cyclic Ylide-Backbone: Angle Dependence of the Donor Strength.

Ylide-substituted phosphines (YPhos) have been shown to be highly electron-rich and efficient ligands in a variety of palladium catalyzed transformations. Here, the synthesis and characterization of novel YPhos ligands containing a cyclic backbone architecture are reported. The ligands are easily synthesized from a cyclic phosphonium salt and the chlorophosphines Cy2PCl (L1) and Cy(FluMe)PCl (L2, with FluMe = 9-methylfluorenyl) and were characterized in both solution and solid states. The smaller PCy2-substituted ligand, L1, readily formed the biscoordinate L12Pd species when treated with Pd2(dba)3 and showed no activity in palladium-catalyzed amination reactions even when applied as defined palladium(II) η3-allyl, t-Bu-indenyl, or cinnamyl precursors. Bulkier fluorenyl-substituted ligand L2 similarly was inactive, despite its ability to form the stable monophosphine complex L2·Pd(dba). Assessment of the electronic properties by experimental and computational methods revealed that L1 and L2 are considerably less electron-rich than previously synthesized YPhos ligands. This was shown to be the result of the small P–C–S bond angle, which is sterically enforced due to the cyclic nature of the backbone. Density functional theory calculations revealed that the small angle results in an increased s-character of the lone pair at the ylidic carbon atom and leads to a polarization of the C–P bond toward the carbon atom, thus decreasing the electron density at the phosphorus atom. The results demonstrate the tunability of the donor strength of YPhos ligands by modification of the ligand backbone beyond simple changes of the substitution pattern and are thus important for future ligand design, with a careful balance of many factors to be considered to achieve catalytic activity.

Synthesis of optically active 3,3’-disubstituted biphenyl derivatives using palladium-catalyzed amination and their evaluation as enantioselective fluorescent detectors for amino alcohols and metal cations

The palladium-catalyzed amination was used to synthesize optically active 3,3’-diaminosubstituted biphenyl derivatives (in particular, macrocyclic derivatives) decorated with additional fluorophore groups (dansyl and 7-methoxycoumarin). The synthesized compounds were studied by spectroscopic methods (UV spectroscopy, fluorescence) in the presence of individual enantiomers of amino alcohols and metal salts. One of the synthesized compounds was demonstrated to serve as an enantioselective fluorescent detector for enantiomers of 2-amino-1-propanol because of different changes in the fluorescence spectra. Certain compounds can be used as molecular probes for the detection of CuII, AlIII, CrIII, and InIII cations due to characteristic changes in the fluorescence spectra upon the addition of metal perchlorates.

Synthesis of optically active 2,7-disubstituted naphthalene derivatives and evaluation of their enantioselective recognition ability

The palladium-catalyzed amination was used to synthesize 2,7-diamino derivatives of naphthalene containing two chiral substituents and fluorophore groups (dansyl, 7-methoxycoumarin, 6,7-dimethoxycoumarin, 6-aminoquinoline). The synthesized compounds were studied by UV absorption and fluorescence spectroscopy in the presence of individual enantiomers of amino alcohols and salts of 21 metals. The possibility of using these compounds as fluorescent detectors for optically active compounds and metals was examined. In the presence of (S)-leucinol, the diquinoline derivative showed enhanced emission with a maximum at shorter wavelengths, which is not typical of its (R) isomer. This fact can be used for the recognition of these enantiomers. A number of naphthalene derivatives can be considered as potential fluorescent chemosensors for CuII cations due to the total fluorescence quenching in the presence of this metal.

Optically Active 10,10′-Spirobi[10H-phenoxasilin]-1,1′-diol: Synthesis, Structure, and Application of its Phosphoramidite Derivative to Palladium-catalyzed Asymmetric Allylic Amination

Optically active (S)-(+)- and (R)-(−)-10,10′-spirobi[10H-phenoxasilin]-1,1′-diols were synthesized by the transesterification of their optically active di-p-toluoyl derivatives resolved by chiral H...

A substituted tricyclohexylphosphane with “conformational lock”

A substituted tricyclohexylphosphane with “conformational lock”, tri(4-trans-(tert-butyl)cyclohexyl)phosphane L, has been designed and synthesized. The ligand has shown similar steric bulkiness and conformations to tricyclohexylphosphane at solid state. The comparable or slightly better performance of ligand L compared to PCy3 in Suzuki-Miyaura coupling has demonstrated the similar steric properties of two ligands in reaction and the effectiveness of the chair conformer of the cyclohexyl rings. The ineffectiveness of both L and PCy3 in palladium-catalyzed aminations has also manifested the weakness of such ligands and a sterically more bulky ligand is needed in order to develop a more efficient amination.

The Quest for the Ideal Base: Rational Design of a Nickel Precatalyst Enables Mild, Homogeneous C-N Cross-Coupling.

Palladium-catalyzed amination reactions using soluble organic bases have provided a solution to the many issues associated with heterogeneous reaction conditions. Still, homogeneous C-N cross-coupling approaches cannot yet employ bases as weak and economical as trialkylamines. Furthermore, organic base-mediated methods have not been developed for Ni(0/II) catalysis, despite some advantages of such systems over those employing Pd-based catalysts. We designed a new air-stable and easily prepared Ni(II) precatalyst bearing an electron-deficient bidentate phosphine ligand that enables the cross-coupling of aryl triflates with aryl amines using triethylamine (TEA) as base. The method is tolerant of sterically congested coupling partners, as well as those bearing base- and nucleophile-sensitive functional groups. With the aid of density functional theory (DFT) calculations, we determined that the electron-deficient auxiliary ligands decrease both the pKa of the Ni-bound amine and the barrier to reductive elimination from the resultant Ni(II)-amido complex. Moreover, we determined that the preclusion of Lewis acid-base complexation between the Ni catalyst and the base, due to steric factors, is important for avoiding catalyst inhibition.

Efficient synthesis of dibenzazepine lactams via a sequential Pd-catalyzed amination and aldol condensation reaction

A simple and efficient reaction was developed for the synthesis of dibenzazepine lactam derivatives. The core 7-membered azepine ring was formed by a stepwise sequence involving a palladium-catalyzed amination and an aldol condensation.

Mechanism-Based Optimization of the Palladium-Catalyzed Amination of Aryl Triflates

Mechanism-Based Optimization of the Palladium-Catalyzed Amination of Aryl Triflates

Tuning the Luminescent Properties of Ruthenium(II) Amino-1,10-Phenanthroline Complexes by Varying the Position of the Amino Group on the Heterocycle.

Eight 1,10-phenanthrolines bearing one or two 2-(1-adamantyloxy)ethylamino substituents attached to different positions of the heterocyclic core were prepared according to SN Ar or palladium-catalyzed amination reactions. Their reaction with cis-Ru(bpy)2 Cl2 (bpy=2,2'-bipyridine) was investigated and Ru(bpy)2 (L)(PF6 )2 (phen=1,10-phenanthroline) (L=amino-substituted 1,10-phenanthroline) complexes were obtained in good yields. The electronic structure and emissive properties of these complexes are strongly dependent on the position of the amino substituent in the heterocycle. Emission bands of the complexes bearing 2- and 4-substituted 1,10-phenanthroline ligands are red-shifted (up to 56 nm) and less intense compared to that of the parent [Ru(phen)(bpy)2 ](PF6 )2 . In contrast, the introduction of the substituent in 3- or 5-position of 1,10-phenanthroline ring induces only small decrease of luminescence and the brightness of the complex with the 3-substituted ligand is comparable to that of the parent complex.

Palladium-Catalyzed C(sp2)-N Bond Cross-Coupling with Triaryl Phosphates.

The first general palladium-catalyzed amination of aryl phosphates is described. The combination of MorDalPhos with [Pd(π-cinnamyl)Cl]2 enables the amination of electron-rich, electron-neutral, and electron-poor aryl phosphates with a board range of aromatic, aliphatic, and heterocyclic amines. Common functional groups such as ether, keto, ester, and nitrile show an excellent compatibility in this reaction condition. The solvent-free amination reactions are also successful in both solid coupling partners. The gram-scale cross-coupling is achieved by this catalytic system.

Hydroaminoalkylation/Buchwald-Hartwig amination sequences for the synthesis of benzo-annulated seven-membered nitrogen heterocycles

Reaction sequences consisting of an initial intermolecular titanium-catalyzed hydroaminoalkylation of a suitably ortho-bromophenyl-substituted alkene and a subsequent intramolecular Buchwald-Hartwig amination are used for the synthesis of benzazepine, benzoxazepine, and benzothiazepine derivatives. While in the latter two cases, the hydroaminoalkylation products obtained from an allyl (2-bromophenyl) ether or an allyl (2-bromophenyl) thioether must be purified prior to the subsequent palladium-catalyzed amination step, both reactions can be combined to an efficient one-pot procedure for the synthesis of 2,3,4,5-tetrahydrobenzo[b]azepines when 4-(2-bromophenyl)-1-butene and various N-methylanilines are used as the starting materials.