A Novel (2,2‐Diarylvinyl)phosphine/Palladium Catalyst for Effective Aromatic Amination

A new series of diarylvinylphosphine ligands was designed and synthesized. A catalyst system, consisting of the ligands and palladium species, effectively catalyzed the coupling reaction of aryl bromides and chlorides with amines to afford the corresponding products in good to excellent yields. The efficiency is likely derived from an interaction between the palladium center and the cis‐aryl moiety on the diarylvinylphosphine ligand stabilizing a catalytic intermediate during the coupling reaction.     

Synthesis of Dienes by Palladium‐Catalyzed Couplings of Tosylhydrazones with Aryl and Alkenyl Halides

Two different combinations of coupling partners can be employed for the synthesis of conjugated dienes by palladium‐catalyzed cross‐coupling with tosylhydrazones: α,β‐unsaturated ketone and aryl halide or alkenyl halide and non‐conjugated tosylhydrazone. Depending on the substrate, a vinylogous hydride elimination is responsible for the formation of the final dienes.     

Ligand‐Free Buchwald–Hartwig Aromatic Aminations of Aryl Halides Catalyzed by Low‐Leaching and Highly Recyclable Sulfur‐Modified Gold‐Supported Palladium Material

A stable heterogeneous catalyst precursor, sulfur‐modified gold‐supported palladium material (SAPd), has proved to be an excellent source of leached, ligand‐free, Pd for the amination of aryl bromides and chlorides. The reaction‐enabling catalyst is provided in situ as leached Pd in low catalyst loading (0.21±0.02 mol%). This allows the precatalyst (SAPd) to be filtered off and used for a minimum of ten reaction cycles without loss of catalytic activity. SAPd released only trace amounts, less than 0.6 ppm, of highly active Pd during the reaction without any aggregation.     

Palladium‐Catalyzed Three‐Component Synthesis of Functionalized Allylamines by Intermolecular Tandem Carbopalladation–Amination

Highly regio‐ and stereoselective formation of allylamines has been achieved through a three‐component reaction between iodobenzene, an allene, and an amine in acetonitrile, catalyzed by in situ formed and by isolated palladium‐diphosphine catalysts.     

Palladium on Carbon‐Catalyzed One‐Pot N‐Arylindole Synthesis: Intramolecular Aromatic Amination,Aromatization, and Intermolecular Aromatic Amination

Indole and indoline derivatives were selectively and temperature dependently synthesized via the intramolecular cross‐coupling reaction between the amino and aromatic bromine functionalities of 2‐bromophenethylamine derivatives in the presence of 10% palladium on carbon (Pd/C), 1,1′‐bis(diphenylphosphino)ferrocene (DPPF), and sodium tert‐butoxide (NaO‐t‐Bu) in mesitylene at 140 and 200 °C, respectively. The neutralization using acetic acid after formation of the indoline derivatives effectively promoted their aromatization, and the corresponding indole derivatives were obtained at 140 °C. Furthermore, various aryl groups were also introduced to the N‐1 position of the indole, pyrrole, and carbazole rings by their direct intramolecular arylation with aryl halides and a one‐pot protocol for N‐arylindole synthesis from 2‐bromophenethylamine was developed.

     

An Efficient Palladium‐NHC (NHC=N‐Heterocyclic Carbene) and Aryl Amination Pre‐Catalyst: [Pd(IPr*)(cinnamyl)Cl]

The well‐defined [Pd(IPr*)(cinnamyl)Cl] complex is reported as one of the best N‐heterocyclic carbene (NHC)‐based pre‐catalysts for the Buchwald–Hartwig amination reaction. This catalytic system displays high efficiency for the coupling of numerous (hetero)aryl chlorides, with a wide range of amines, at room temperature or at extremely low catalyst loading (as low as 0.025 mol%).     

Palladium‐Catalyzed Aryl Amination Reactions of 6‐Bromo‐ and 6‐Chloropurine Nucleosides

Palladium‐catalyzed C N bond forming reactions of 6‐bromo‐ as well as 6‐chloropurine ribonucleosides and the 2′‐deoxy analogues with arylamines are described. Efficient conversions were observed with palladium(II) acetate/Xantphos/cesium carbonate, in toluene at 100 °C. Reactions of the bromonucleoside derivatives could be conducted at a lowered catalytic loading [5 mol% Pd(OAc)₂/7.5 mol% Xantphos], whereas good product yields were obtained with a higher catalyst load [10 mol% Pd(OAc)₂/15 mol% Xantphos] when the chloro analogue was employed. Among the examples evaluated, silyl protection for the hydroxy groups appears better as compared to acetyl. The methodology has been evaluated via reactions with a variety of arylamines and by synthesis of biologically relevant deoxyadenosine and adenosine dimers. This is the first detailed analysis of aryl amination reactions of 6‐chloropurine nucleosides, and comparison of the two halogenated nucleoside substrates.     

Palladium‐Catalyzed Cross‐Coupling Reaction Using Arylgermanium Sesquioxide

Powdery reagents obtained by complete alkaline hydrolysis of arylgermanium trichlorides were found to undergo the palladium‐catalyzed cross‐coupling reaction with aryl bromides and iodides in good yields. The reaction is performed in an aqueous medium taking sodium hydroxide as an activator. Some base‐sensitive functionalities such as acetyl and trifluoromethyl groups survived the reaction.     

钯催化卤代芳烃的胺化反应研究

钯催化卤代芳烃胺化是形成CAr-N的重要方法。配体的发展扩展了底物的适用范围，提高了反应的选择性，实现了廉价易得的氯代芳烃的胺化，弱碱的使用提高了官能团的兼容性，因此Pd催化芳胺化广泛应用于合成芳胺类化合物。本文以卤代芳烃为线索，对钯催化偶联胺化反应的研究进展进行了综述和展望。     

Reusable,Polymer‐Supported,Palladium‐Catalyzed,Atom‐ Efficient Coupling Reaction of Aryl Halides with Sodium Tetraphenylborate in Water by Focused Microwave Irradiation

A rapid and efficient cross‐coupling reaction of sodium tetraphenylborate with aryl bromides was carried out in water at 120 °C in the presence of a polymer‐supported palladium catalyst and potassium carbonate under focused microwave irradiation. All four phenyl groups of sodium tetraphenylborate participated in the reaction and produced polyfunctional biaryls in excellent yields. The polymeric catalyst can be easily separated from the reaction mixture and reused more than 10 times without showing any decrease in activity.     

2,6‐Diisopropoxyphenyl(dicyclohexyl)phosphine: A New Ligand for Palladium‐Catalyzed Amination Reactions of Aryl Chlorides with Potassium Hydroxide as the Base

A new, readily available monophosphine tetrafluoroborate salt [ L2 ⋅ HBF₄ ] was developed for the palladium‐catalyzed amination reaction of aryl chlorides in moderate to high yields with the cheap and easily available potassium hydroxide as the base. The reaction enjoys a wide scope, lower reaction temperatures, shorter reaction times, high yields, and low catalyst loading when compared to some of same amination reactions reported in the literature. Based on a kinetic study, ³¹P NMR measurements, and DFT calculations, a mechanism involving a 1:1 Pd/L species is proposed.     

A General and Practical Palladium‐Catalyzed Direct α‐Arylation of Amides with Aryl Halides

An efficient system for the direct catalytic intermolecular α‐arylation of acetamide derivatives with aryl bromides and chlorides is presented. The palladium catalyst is supported by Kwong’s indole‐based phosphine ligand and provides monoarylated amides in up to 95% yield. Excellent chemoselectivities (>10:1) in the mono‐ and diarylation with aryl bromides were achieved by careful selection of bases, solvents, and stoichiometry. Under the coupling conditions, the weakly acidic α‐protons of amides (pK_a up to 35) were reversibly depotonated by lithium tert‐butoxide (LiO‐t‐Bu), sodium tert‐butoxide (NaO‐t‐Bu) or sodium bis(trimethylsilyl)amide [NaN(SiMe₃)₂].

     

Palladium‐Catalyzed Methoxylation of Aromatic Chlorides with Borate Salts

Herein we disclose a simple palladium‐catalyzed transformation for the methoxylation of aromatic chlorides with tetramethoxyborate salts. The procedure provides a new and efficient synthetic tool for the introduction of a methoxy group into aromatic systems. In addition, the reaction can be achieved using a wide range of aromatic and heteroaromatic chlorides, the cheapest class of halides.

     

Synthesis of N‐Arylamides by Copper‐Catalyzed Amination of Aryl Halides with Nitriles

A copper‐catalyzed amination of aryl halides with nitriles has been developed. The use of nitriles as nitrogen nucleophiles can make the synthesis of N‐arylamides more simple than that using amides through in‐situ hydrolysis. A variety of N‐arylamides and benzoxazole derivatives can be synthesized according to this approach.     

Evaluation of Aromatic Amination Catalyzed by Palladium on Carbon: A Practical Synthesis of Triarylamines

A heterogeneous palladium on carbon (Pd/C)‐catalyzed coupling between amines and aromatic halides including aromatic chlorides has been achieved using sodium tert‐butoxide (NaO‐t‐Bu) and 1,1′‐bis(diphenylphosphino)ferrocene (dppf) as a ligand in cyclopentyl methyl ether (CPME). The use of potassium tert‐butoxide (KO‐t‐Bu) in place of NaO‐t‐Bu brought about the benzyne‐mediated aromatic amination even without Pd/C and dppf, giving a mixture of regioisomers when 4‐substituted bromobenzenes were employed as the substrate. The combination of Pd/C, dppf, NaO‐t‐Bu could be utilized for the syntheses of a broad range of triarylamines by replacing CPME with mesitylene which can provide a higher reaction temperature. The Pd/C could be quantitatively recovered and reused until at least the fourth cycle without any loss in catalytic activity. The quite low leaching of palladium (<1.1%) was demonstrated by an inductively coupled plasma‐atomic emission spectrometric analysis.     

A New Chiral P,N‐Ligand Derived from 1‐Phenylphospholane‐2‐carboxylic Acid (Phenyl‐P‐proline) for Palladium‐Catalyzed Asymmetric Allylic Substitution Reactions

New types of P,N‐ligands, cis‐ and trans‐ 3 , containing a tetrahydroisoquinoline skeleton as an N‐donor were synthesized from (1R,2S)‐1‐phenylphospholane‐2‐carboxylic acid (phenyl‐P‐proline, 1 ). The cis isomer, cis‐ 3 , was found to act as an excellent ligand in palladium‐catalyzed asymmetric allylic substitution reactions. The reactions of 1,3‐diphenyl‐2‐propenyl acetate ( 5 ) with several nucleophiles in the presence of [Pd(π‐allyl)Cl]₂, cis‐ 3 (Pd : ligand=1 : 2), and a base afforded the desired products in high yields with high enantioselectivity. It was suggested that these ligands did not serve as P,N‐bidentate ligands but as P‐monodentate ligands in these reactions.     

Examination of the Aromatic Amination Catalyzed by Palladium on Charcoal

The Buchwald–Hartwig amination of aryl halides with secondary amines and functionalized aromatic amines catalyzed by solid‐supported palladium is reported. The choices of ligand, base and solvent are crucial for the successful coupling. The amination of aromatic iodides, bromides and chlorides can be easily achieved with palladium on charcoal in the presence of a biphenylphosphane‐type ligand at 80–110 °C. In addition, the palladium on charcoal catalyst is easily separable after the reaction, and reusable several times with only small activity loss.     

Oxaphosphole‐Based Monophosphorus Ligands for Palladium‐Catalyzed Amination Reactions

A novel class of C‐2‐substituted oxaphosphole‐based monophosphines 1–4 has been synthesized. Palladium complexes derived from these ligands and their C‐2‐unsubstituted analogs provide general catalysts for amination reactions of challenging aryl and heteroaryl halides with sterically hindered anilines and alkylamines.     

Efficient Synthesis of Substituted Selenophenes Based on the First Palladium(0)‐Catalyzed Cross‐Coupling Reactions of Tetrabromoselenophene

Regioselective Suzuki cross‐coupling reactions of tetrabromoselenophene allow a convenient synthesis of aryl‐substituted selenophenes. High yields were obtained using a novel biaryl‐monophosphine ligand. The first tetra(1‐alkynyl)selenophene was prepared in one step by a Sonogashira reaction of tetrabromoselenophene.     

Palladium/Proazaphosphatrane‐Catalyzed Amination of Aryl Halides Possessing a Phenol,Alcohol, Acetanilide,Amide or an Enolizable Ketone Functional Group: Efficacy of Lithium Bis(trimethylsilyl)amide as the Base

A commercially available catalyst system comprising Pd(OAc)₂ or Pd₂(dba)₃ and the proazaphosphatrane ancillary ligand P(i‐BuNCH₂CH₂)₃N ( 1 ) for the amination of aryl halides substituted with a phenol, alcohol, acetanilide, amide or ketone group containing an enolizable hydrogen is described. The reaction is performed in the presence of LiN(SiMe₃)₂ as the base. Other bases tested were either less effective or completely non‐functional.