A Robust and Broadly Applicable Cobalt‐Catalyzed Cross‐Coupling of Functionalized Bench‐Stable Organozinc Pivalates with Unsaturated Halides

We report a robust and broadly applicable CoCl₂‐catalyzed cross‐coupling between functionalized aryl and heteroaryl zinc pivalates and various electron‐poor aryl and heteroaryl halides (X=Cl, Br, I). Couplings with (E)‐ or (Z)‐bromo‐ or iodo‐alkenes proceed with retention of configuration. Also, alkynyl bromides react with arylzinc pivalates providing arylated alkynes.     

Microwave‐Assisted Synthesis of Arylated Pyrrolo[2,1‐a]Isoquinoline Derivatives via Sequential [3 + 2] Cycloadditions and Suzuki‐Miyaura Cross‐Couplings in Aqueous Medium

Treatment of 5‐bromo‐2‐(bromoacetyl)thiophene ( 1 ) with isoquinoline gave the isoquinolinium bromide 2 . Reaction of 2 with acrylic acid derivatives, in the presence of MnO₂, afforded the 3‐[(5‐bromothiophen‐2‐ylcarbonyl]pyrrolo[2,1‐a]‐isoquinolines 3a , 3b . Suzuki–Miyaura cross‐coupling reactions of the bromides 3a , 3b in aqueous solvent with several activated and deactivated aryl(hetaryl)boronic acids 4a , 4b , 4c , 4d , 4e , 4f using a Pd(II)‐complex under thermal heating as well as microwave‐irradiating conditions afforded the corresponding new arylated pyrrolo[2,1‐a]isoquinoline derivatives 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 in high to excellent isolated yields.     

Pd(0)‐Catalyzed Tandem One‐Pot Reaction of Biphenyl Ketones/Aldehydes to the Corresponding Di‐substituted Aryl Olefins

Synthesis of di‐substituted aryl olefins via a Pd(0)‐catalyzed cross‐coupling reaction of biphenyl ketones/aldehydes, tosylhydrazide, and aryl bromides (or benzyl halides) was developed. This methodology was achieved by one‐pot two‐step reactions involving the preparation of N ‐tosylhydrazones by reacting tosylhydrazide with biphenyl ketones/aldehydes, followed by coupling with aryl bromides (or benzyl halides) in the presence of Pd(PPh₃ )₄ and lithium t ‐butoxide to produce various di‐substituted aryl olefins in moderate to good yields.     

Oxazoles formation during O‐alkylation of isonitroso‐naphthols. X‐ray structure of [1,2]naphthoquinone 1‐[O‐(4‐tert‐butyl‐benzyl)‐oxime] and 2‐(4‐tert‐butyl‐phenyl)napth[1,2‐d]oxazole

1‐Nitroso‐2‐naphthol and 2‐nitroso‐1‐naphthol, both in the isonitroso form, react with benzyl bromides in THF and in the presence of triethylamine affording, in low yields, the corresponding O‐benzyl oximes and 2‐aryl naphthoxazoles in a 1:1 ratio, approximately. The structures of O‐benzyl oximes and naphthoxazoles isolated have been determined by X‐ray analysis.     

在催化体系可回收和无配体条件下溴化四丁基铵中钯催化卤代芳烃与芳基硼酸的Suzuki-Miyaura交叉偶联反应

我们发展一种在催化体系可回收和无配体条件下溴化四丁基铵（TBAB）中钯催化卤代芳烃与芳基硼酸的Suzuki-Miyaura交叉偶联反应方法。我们发现水的量对反应有很大的影响。当水的用量为1 %（质量比）时,反应的结果最好。在3 mol%的醋酸钯和1.5 g的TBAB（含1%的水）,一系列卤代芳烃与芳基硼酸的顺利地发生Suzuki-Miyaura交叉偶联反应,得到中等及良好的产率。而且在溴代芳烃和活泼的氯代芳烃的交叉反应中,Pd(OAc)2/TBAB催化体系可以回收重复使用多次,并且催化活性基本不变。     

Heck reactions of aryl halides with alk‐1‐en‐3‐ol derivatives catalysed by a tetraphosphine–palladium complex

cis,cis,cis‐1,2,3,4‐Tetrakis(diphenylphosphinomethyl)cyclopentane–[PdCl(C₃H₅)]₂ efficiently catalyses the Heck reaction of alk‐1‐en‐3‐ol with a variety of aryl halides. In the presence of hex‐1‐en‐3‐ol or oct‐1‐en‐3‐ol, the β‐arylated carbonyl compounds were selectively obtained. Turnover numbers up to 84 000 can be obtained for this reaction. Linalool and 2‐methylbut‐3‐en‐2‐ol led regio‐ and stereoselectively to the corresponding (E)‐1‐arylalk‐1‐en‐3‐ol derivatives. A minor electronic effect of the substituents of the aryl bromide was observed. Quite similar reaction rates were generally observed in the presence of activated aryl bromides such as bromoacetophenone and deactivated aryl bromides such as bromoanisole, indicating that, with these alkenols and this catalyst, the oxidative addition of aryl bromides to palladium is not the rate‐limiting step. It should be noted that this reaction also proceeds with sterically very congested aryl bromides such as 9‐bromoanthracene or 2,4,6‐triisopropylbromobenzene or with a vinyl bromide. On the other hand, low yields were obtained with aryl chlorides. Copyright © 2006 John Wiley & Sons, Ltd.     

Methenamine as an Efficient Ligand for Copper‐catalyzed Coupling of Phenols with Aryl Halides

Employing methenamine as a new supporting ligand, the copper‐catalyzed coupling reactions of aryl bromides or aryl iodides with various phenols successfully proceeded in good yields under mild conditions. A series of diaryl ethers were obtained with excellent yields in the presence of K₃PO₄ and copper(I) salt.     

Synthesis of 2,5,7‐Triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles by Reaction of 5(3)‐Amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with Chalcones

The reaction of 5(3)‐amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with 1,3‐diaryl‐2‐propen‐1‐ones (chalcones) in refluxing DMF leads to 2,5,7‐triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles. In DMSO solution, the latter exist in equilibrium of two tautomeric 4,7‐dihydropyrazolo[1,5‐a]pyrimidines and 6,7‐dihydropyrazolo[1,5‐a]pyrimidines in various ratios, depending on the nature of aryl substituents in chalcone building blocks.     

An Efficient Palladium and Bis(2‐pyridylmethyl)amine‐based System for Suzuki‐Miyaura Cross‐Coupling under Aqueous and Aerobic Condition

A novel PdCl₂/bis(2‐pyridylmethyl)amine‐based ligand ( 1 ) catalytic system, which is water‐soluble and air‐stable, has been successfully synthesized and applied for Suzuki‐Miyaura cross‐coupling reaction. In the presence of catalytic amount of PdCl₂/ 1 system, arylboronic acids can couple with a wide range of aryl halides, including aryl bromides and aryl chlorides. The reactions proceed under mild conditions to give excellent yields, and a wide range of functionalities is tolerated.     

Metal‐Free 2,2,6,6‐Tetramethylpiperidin‐1‐yloxy Radical (TEMPO) Catalyzed Aerobic Oxidation of Hydroxylamines and Alkoxyamines to Oximes and Oxime Ethers

TEMPO‐Mediated oxidation of hydroxylamines (=hydroxyamines) and alkoxyamines to the corresponding oxime derivatives is reported (TEMPO=2,2,6,6‐tetramethylpiperidin‐1‐yloxy radical; Scheme 2). These environmentally benign oxidations proceed in good to excellent yields (Table 1). For alkoxyamines, oxidation to the corresponding oxime ethers can be performed by using dioxygen as a terminal oxidant in the presence of 5–10 mol‐% of TEMPO or 4‐substituted derivatives thereof as a catalyst (Scheme 3 and Table 2). Importantly, benzyl bromides can directly be transformed to oxime ethers via in situ alkoxyamine formation by a nucleophilic substitution followed by TEMPO‐mediated oxidation (Scheme 4 and Table 3).     

A Facile Approach to Oximes and Ethers by a Tandem NO+‐Initiated Semipinacol Rearrangement and H‐Elimination

An efficient oximation method has been developed on the basis of NO⁺‐initiated semipinacol rearrangement and subsequent proton elimination. The procedure enabled the rapid construction of a series of oximes and oxime ethers with spiro quaternary stereocenters from allylic silyl ethers. Additional features of this reaction include wide substrate tolerance as well as the commercial availability of the safe nitrosation reagent NOBF₄. The key N‐heterotricyclic cores of three natural alkaloids, tuberostemoninol B, (+)‐quebrachidine, and an insecticide, were also constructed efficiently by this method.     

CuO Nanoparticles as Effective Reusable Heterogeneous Catalyst for S‐Arylation Reactions

Copper(II) oxide nanoparticles have been synthesized from Cu(OAc)₂ via a simple hydrolysis route and were found to be an efficient and inexpensive catalyst for ligand free C? S cross‐coupling reactions of malononitrile? CS₂ adduct with various aryl halides. Aryl iodides and bromides, with electron‐withdrawing as well as electron‐releasing groups on the aromatic ring, undergo coupling reactions in good yields.     

Reaction Optimization,Scalability, and Mechanistic Insight on the Catalytic Enantioselective Desymmetrization of 1,1‐Diborylalkanes via Suzuki–Miyaura Cross‐Coupling

A method for enantioselective desymmetrization of 1,1‐diborylalkanes through a stereoselective Pd‐catalyzed Suzuki–Miyaura cross‐coupling has been thoroughly optimized. The most effective ligand was found to be a α,α,α,α‐tetra‐aryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL)‐derived phosphoramidite. Results show that in order to achieve high selectivity, a suitable balance between the sterics of the aryl groups and the amino group on the ligand must be achieved. While the base has been known to facilitate transmetallation in cross‐coupling reactions, mechanistic studies on this desymmetrization process reveal that the base, in the presence of KHF₂, likely plays an additional role in the hydrolysis of the pinacol boronates to the corresponding boronic acids. Through an in depth optimization of the chiral ligand and mechanistic studies, it was possible to obtain ee values over 90 % for several aryl bromides and to develop a reliably scalable process (up to one gram of 1,1‐diborylalkane substrate).     

Synthesis of Enaminone‐Pd(II) Complexes and Their Application in Catalysing Aqueous Suzuki‐Miyaura Cross Coupling Reaction

A series of Pd(II)‐enaminone complexes, termed Pd(eao)₂, have been synthesized and characterized. The investigation on the catalytic activities of these new Pd(II)‐reagents has proved that the Pd(eao)₂‐ 1 possesses excellent catalytic activity for the Suzuki‐ Miyaura cross coupling reactions of aryl bromides/chlorides with aryl/vinyl boronic acids in the environmentally benign media of aqueous PEG400 at low loading (5 mol‰). The superiority of this Pd(II)‐reagent to those commercial Pd(II) and Pd(0) catalysts in catalyzing the reactions has been confirmed by parallel experiments. What's more, Pd(eao)₂‐ 2 has been found as a practical catalyst for the homo‐coupling reactions of aryl boronic acids.     

Desulfinative palladium‐catalyzed cross‐coupling of arylsulfonyl hydrazides with aryl bromides under air

A highly efficient and mild palladium‐catalyzed cross‐coupling of arylsulfonyl hydrazides and aryl bromides for the selective synthesis of unsymmetrical biaryls has been developed. This methodology has the advantages of easily accessible starting materials, functional group tolerance and a wide range of substrates, which provide rapid access to biaryls derivatives. In this protocol, abundant and stable aryl bromides serve as the aryl sources by coupling reaction of the aryl group generated from arylsulfonyl hydrazides via in situ release of nitrogen and sulfur dioxide. No external oxidants or acids are needed for this kind of transformation.     

Nickel‐Catalyzed Cross‐Electrophile Coupling of Aryl Bromides with Pyrimidin‐2‐yl Tosylates

A new protocol for the NiCl₂ ‐catalyzed cross‐electrophile coupling of aryl bromides with pyrimidin‐2‐yl tosylates to give the corresponding C2 ‐arylation pyrimidine derivatives has been developed. This study provides an improvement over previous methods by using pyrimidin‐2‐yl tosylates instead of halides as coupling partners that are stable and easily available.     

Stereospecific 1,4‐Metallate Shift Enables Stereoconvergent Synthesis of Ketoximes

Reported herein is a stereospecific 1,4‐metallate rearrangement for single‐geometry ketoxime synthesis from oxime chlorides and arylboronic acids. This strategy exhibits broad substrate scope with excellent stereoselectivity under mild reaction conditions. In comparison with the conventional approaches, each configuration of unsymmetric diaryl oximes, as well as the thermodynamically less stable Z isomer of aryl alkyl ketoximes can be selectively and exclusively obtained. The reactivities of unsymmetric diaryl oximes and the Z isomer of aryl alkyl oximes, a class of underexplored molecules, enables efficient access to the corresponding isoquinolines, isoquinoline N‐oxides, and amides having a single configuration.     

Copper(I)‐Catalyzed Intramolecular Direct C‐Arylation of Azoles with Aryl Bromides

A concise route to access 5H‐imidazo[2,1‐a]isoindole heterofused compounds by copper(I)‐catalyzed intramolecular coupling of non‐activated aryl bromides with azoles is reported. With CuI as catalyst, 1,10‐phenanthroline as ligand, and K₃PO₄ as base, the reactions of 1‐(2‐bromobenzyl)‐1H‐imidazoles in DMF/o‐xylene (1:1, V:V) at 145°C afford the corresponding substituted 5H‐imidazo[2,1‐a]isoindoles in high yields via intramolecular C‐arylation.     

N‐Arylation of N‐H heterocycles with aryl bromides and aryl iodides using cui and kf/Al2O3

Copper‐catalyzed system for N‐arylation of N‐H group in heterocycles such as indole, pyrrole and carbazole with aryl iodides and aryl bromides using potassium fluoride supported on alumina as a base is described. This is a simple and efficient method for the coupling of aryl iodides and bromides with N‐H heterocycles. Different functionalized iodo and bromo arenes were coupled with N‐H heterocycles using this system.     

Oxidative Coupling of Aryl Boron Reagents with sp3‐Carbon Nucleophiles: The Enolate Chan–Evans–Lam Reaction

Reported is a versatile new oxidative method for the arylation of activated methylene species. Under mild reaction conditions (RT to 40 °C), Cu(OTf)₂ mediates the selective coupling of functionalized aryl boron species with a variety of stabilized sp³‐nucleophiles. Tertiary malonates and amido esters can be employed as substrates to generate quaternary centers. Complementing either traditional cross‐coupling or S_NAr protocols, the transformation is chemoselective in the presence of halogen electrophiles, including aryl bromides and iodides. Substrates bearing amide, sulfonyl, and phosphonyl groups, which are not amenable to coupling under mild Hurtley‐type conditions, are suitable reaction partners.