Buchwald-Hartwig Cross-coupling Research Articles

Application of Suzuki-Miyaura and Buchwald-Hartwig Cross-coupling Reactions to the Preparation of Substituted 1,2,4-Benzotriazine 1-Oxides Related to the Antitumor Agent Tirapazamine.

Many 1,2,4-benzotriazine 1,4-dioxides display the ability to selectively kill the oxygen-poor cells found in solid tumors. As a result, there is a desire for synthetic routes that afford access to substituted 1,2,4-benzotriazine 1-oxides that can be used as direct precursors in the synthesis of 1,2,4-benzotriazine 1,4-dioxides. Here we describe the use of Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions for the construction of various 1,2,4-benzotriazine 1-oxide analogs bearing substituents at the 3-, 6-, and 7-positions.

ChemInform Abstract: Advances in Metal‐catalyzed Cross‐coupling Reactions of Halogenated Quinazolinones and Their Quinazoline Derivatives

AbstractReview: 57 refs.

Cascade imination, Buchwald–Hartwig cross coupling and cycloaddition reaction: synthesis of pyrido[2,3-d]pyrimidines

A new approach for the synthesis of pyrido[2,3-d]pyrimidines via cascade imination/Buchwald–Hartwig cross coupling/cycloaddition reactions is described.

Advances in metal-catalyzed cross-coupling reactions of halogenated quinazolinones and their quinazoline derivatives.

Halogenated quinazolinones and quinazolines are versatile synthetic intermediates for the metal-catalyzed carbon–carbon bond formation reactions such as the Kumada, Stille, Negishi, Sonogashira, Suzuki-Miyaura and Heck cross-coupling reactions or carbon-heteroatom bond formation via the Buchwald-Hartwig cross-coupling to yield novel polysubstituted derivatives. This review presents an overview of the application of these methods on halogenated quinazolin-4-ones and their quinazolines to generate novel polysubstituted derivatives.

A new DMAP-catalyzed and microwave-assisted approach for introducing heteroarylamino substituents at position-4 of the quinazoline ring

We report herein a new methodology for synthesizing quinazoline derivatives bearing a heteroarylamino moiety at position-4 of the quinazoline ring. As an alternative to the Buchwald–Hartwig cross-coupling reaction, which appears, until now, as the only efficient way to react 4-chloroquinazolines with numerous amino nitrogen-containing heterocycles displaying poor nucleophilicity, we developed a DMAP-catalyzed reaction involving microwave irradiation. Optimization of the reaction conditions led to the use of 30 mol % of DMAP in toluene, using a monomode microwave reactor and sealed vials. Moreover, the SNAr reaction intermediate salt was isolated and fully characterized. Finally, the procedure was extended to two different 2-substituted-quinazoline series and also to various anilines, demonstrating that this approach was a general efficient way to access to such 4-substituted quinazoline scaffolds of high pharmaceutical interest.

Synthesis and biological evaluation of substituted 2-anilino-7H-pyrrolopyrimidines as PDK1 inhibitors

An efficient and scalable route for a series of novel substituted 2-anilino-7H-pyrrolopyrimidine compounds as potential inhibitors of PDK1, an important regulator of the PI3K/Akt pathway that is dysregulated in many cancers, was developed and is described. The synthetic strategy was designed around Suzuki and Buchwald–Hartwig cross-couplings of a boronate fragment and various customised anilines sequentially with 2,4-dichloro-7-tosyl-7H-pyrrolopyrimidine. All fragments were constructed separately and cross-coupled to provide access to a range of novel compounds. Biological evaluation of these was undertaken, with modest inhibition observed.

Synthesis and biological evaluation of substituted 3-anilino-quinolin-2(1H)-ones as PDK1 inhibitors

PDK1 is an important regulator of the PI3K/Akt pathway, which has been found frequently activated in a large number of human cancers. Herein we described the preparation of novel substituted 3-anilino-quinolin-2(1H)-ones as PDK1 inhibitors. The synthesis is based around a Buchwald–Hartwig cross-coupling of various 3-bromo-6-substituted-quinolin-2(1H)-ones with three different functionalised anilines. The modular nature of the designed synthesis allowed access to a series of novel inhibitors through derivatisation of a late-stage intermediate. All compounds were screened against isolated PDK1 enzyme, with modest inhibition observed.

Buchwald–Hartwig reactions in water using surfactants

Examination of the scope and limitation of the Buchwald–Hartwig cross-coupling reaction in micellar medium is reported. An array of aryl or heteroaryl halides were coupled to diverse nitrogen coupling partners using a combination of [(allyl)PdCl]2 and cBRIDP to afford the corresponding products in moderate to excellent yields. 30 examples are reported, including polar solid and fairly water-soluble organic substrates/reagents.

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

A straightforward and scalable eight-step synthesis of new N-heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2-nitro-m-xylene. This process allows for the preparation of a novel class of NHCs coined ITent ("Tent" for "tentacular") of which the well-known IMes (N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (N,N'-bis(2,6-di(2-propyl)phenyl)imidazol-2-ylidene) and IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene), IHept (N,N'-bis(2,6-di(4-heptyl)phenyl)imidazol-2-ylidene) and INon (N,N'-bis(2,6-di(5-nonyl)phenyl)imidazol-2-ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-couplings was investigated.

Palladium-Catalyzed Intermolecular Aerobic Oxidative Cyclization of 2-Ethynylanilines with Isocyanides: Regioselective Synthesis of 4-Halo-2-aminoquinolines

A robust and regioselective palladium-catalyzed intermolecular aerobic oxidative cyclization of 2-ethynylanilines with isocyanides to the synthesis of 4-halo-2-aminoquinolines is reported herein. The procedure constructs various 4-halo-2-aminoquinolines with moderate to excellent yields (47-94%) and broad substrates scope. Furthermore, this process can be easily extended to synthesis of various 6H-indolo[2,3-b]quinolines via an intramolecular Buchwald-Hartwig cross-coupling reaction in two-step one-pot manner.

Synthesis and pharmacological investigation of new N-hydroxyalkyl-2-aminophenothiazines exhibiting marked MDR inhibitory effect

Novel N-hydroxyalkyl-2-aminophenothiazines implying a tetrazole moiety at the alkyl chain have been synthesized by hydroboration–oxidation of dienes followed by Buchwald–Hartwig cross-coupling reaction. Also, some sulfoxide and sulfone derivatives have been prepared by selective oxidations. MDR inhibition studies on rat hepatocyte cell culture revealed that some derivatives exhibit marked biological efficacy exceeding that of the standard verapamil (e.g., 3h, 4h, 16). Selected derivatives were subjected to chemical resolution to provide both enantiomers which were shown of similar activity on P-gp interaction measurements. The new compounds exhibited no toxicity.

Delineating Poly(Aniline) Redox Chemistry by Using Tailored Oligo(Aryleneamine)s: Towards Oligo(Aniline)‐Based Organic Semiconductors with Tunable Optoelectronic Properties

The simple and elegant Buchwald-Hartwig cross-coupling reaction has been used to synthesise a designed range of new aniline-based tetramers in one step, and without the need for protecting groups. Variation of the central aromatic ring has provided the opportunity to carefully tune the optoelectronic properties in this series, thus enabling a structure-activity relationship study by using a range of photophysical and electrochemical techniques. As a result, the long-proposed sequences of electron-electron (EE) and electron-chemical (EC) processes that support the complex redox and proton-transfer reactions involved in the well-known switching of redox states of poly- and oligo(aniline)s are revealed here for the first time. We also present the initial results from time-dependent DFT calculations to clarify the optoelectronic behaviour of these oligomers. The dc-conductivity measurements of conducting thin films of this series, doped with the prototypical poly(aniline) protonating agent D,L-camphor-10-sulfonic acid (CSA), externally plasticised with triphenyl phosphate (TPP), and processed from m-cresol (MC) solutions, are also presented.

Application of 6,7-Indole Aryne Cycloaddition and Pd(0)-Catalyzed Suzuki–Miyaura and Buchwald–Hartwig Cross-Coupling Reactions for the Preparation of Annulated Indole Libraries

The construction of an unprecedented class of an indole-based library, namely, a 6,7-annulated-4-substituted 93-member indole library, using a strategic combination of 6,7-indolyne cycloaddition and cross-coupling reactions under both Suzuki-Miyaura and Buchwald-Hartwig conditions is described. This work represents the first example of library development that employs the indole aryne methodology. Annulated indoles, with the exception of only a few biologically active natural products (i.e., the trikentrins, herbindoles, teleocidins, and nodulisporic acids), have no representation in the PubChem or MLSMR databases. These structural entities are therefore predicted to have unique chemical property space characteristics and a high probability of exhibiting interesting biological activity.

Novel thalidomide analogues with potent NFκB and TNF expression inhibition

A series of N-phenyl thalidomide analogues have been prepared efficiently through a Buchwald–Hartwig cross coupling reaction as the key step. Several of these compounds have extraordinary TNF expression inhibition compared to both thalidomide and the current pharmaceutical agent Revlimid (Lenalidomide).

Synthesis of 7‐Aminocoumarin by Buchwald–Hartwig Cross Coupling for Specific Protein Labeling in Living Cells

To enable minimally invasive studies of proteins in their native context, it is desirable to tag proteins with small, bright reporter groups. Recently, our lab described PRIME (probe incorporation mediated by enzymes) technology for such tagging.[1–3] An engineered variant of Escherichia coli lipoic acid ligase (LplA) is used to covalently attach a fluorescent substrate, such as 7-hydroxycoumarin, onto a 13-residue peptide-recognition sequence (called LAP, for ligase acceptor peptide) that is genetically fused to a protein of interest (POI; Scheme 1A). The targeting specificity is derived from the extremely high natural sequence specificity of LplA.[4] PRIME was used to label and visualize various LAP-tagged cytoskeletal and adhesion proteins in living mammalian cells.

Substituted 2,5-diazabicyclo[4.1.0]heptanes and their application as general piperazine surrogates: synthesis and biological activity of a Ciprofloxacin analogue

Piperazines and modified piperazines, such as homopiperazines and 2-methylpiperazines, are found in a wide range of pharmaceutical substances and biologically active molecules. In this study 2,5-diazabicyclo[4.1.0]heptanes, in which a cyclopropane ring is fused onto a piperazine ring, are described as modified piperazine analogues. Differentially N, N′-disubstituted and N-monosubstituted compounds can be readily prepared from 2-ketopiperazine in a few steps, using a Simmons–Smith reaction of 1,2,3,4-tetrahydropyrazines with diethylzinc and diiodomethane for the key cyclopropane ring formation. An analogue of the fluoroquinolone antibacterial Ciprofloxacin was synthesized using a palladium-catalyzed Buchwald–Hartwig cross-coupling to attach the diazabicyclo[4.1.0]heptane core to the 7-position of the fluoroquinolone core. The resultant analogue was demonstrated to have similar antibacterial activity to the parent drug Ciprofloxacin. X-ray crystallographic analysis of this analogue reveals a distorted piperazine ring in the diazabicyclo[4.1.0]heptane core. The p K a of the conjugate acid of N-Cbz-monoprotected 2,5-diazabicyclo[4.1.0]heptane was determined to be 6.74±0.05, which is 1.3 p K a units lower than the corresponding N-Cbz-monoprotected piperazine compound. The lower basicity of diazabicyclo[4.1.0]heptanes is due to the electron-withdrawing character of the adjacent cyclopropane rings. The modified physicochemical and structural properties of diazabicyclo[4.1.0]heptanes relative to piperazines are expected to lead to interesting changes in the pharmacokinetic and biological activity profile of these molecules.

Practical Synthesis of 1-(7-Fluoro-naphthalen-1-yl)piperazine Hydrochloride

A practical and scalable preparation of 1-(7-fluoronaphthalen-1-yl)-piperazine hydrochloride (1) is reported. The original route for the synthesis of this compound involved the use of 1-amino-7-fluoronaphthalene and bis(2-chloroethyl)amine hydrochloride, two highly toxic compounds. A new protocol has been developed that employs a palladium-catalyzed Buchwald–Hartwig cross-coupling reaction between 1-Boc-piperazine and 1-bromo-7-fluoronaphthalene followed by piperazine deprotection with HCl gas. In addition, an efficient palladium removal protocol allowed for the preparation of the target molecule with less than 20 ppm of this metal. This methodology has been successfully implemented to produce multigram quantities of 1 with excellent purity and low palladium content.

Synthesis and antioxidant activity evaluation of new 7-aryl or 7-heteroarylamino-2,3-dimethylbenzo[ b]thiophenes obtained by Buchwald–Hartwig C–N cross-coupling

New 7-aryl or 7-heteroarylamino-2,3-dimethylbenzo[ b]thiophenes were prepared by palladium-catalyzed Buchwald–Hartwig cross-coupling of 7-bromo or 7-amino-2,3-dimethylbenzo[ b]thiophenes, previously prepared by us, with substituted (4-methoxy or 3,4-dimethoxy) anilines and 3-aminopyridine or with substituted (3-methoxy or 4-cyano) bromobenzenes and 2-bromopyridine, respectively, using Pd(OAc) 2, rac-BINAP or Xantphos as ligands, and Cs 2CO 3 as base. Their antioxidant properties were evaluated by several methods: reducing power, scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, inhibition of erythrocyte hemolysis and inhibition of lipid peroxidation using the β-carotene linoleate system. EC 50 values for all the methods were determined and it was possible to establish some structure–activity relationships (SARs) based on the presence and position of different substituents on the phenyl ring (1 or 2 OMe and C N), on the presence of a pyridine ring and on the position of its nitrogen atom relative to the N–H bond.

A General, Modular Approach to a New Family of Amine-Substituted Arylboronic Acid Saccharide Chemosensors

A general synthetic approach towards a class of water-soluble, high quantum yield fluorescent saccharide reporters using 6-morpholinonaphthalene-2-yl boronic acid as an illustrative case is reported. The strength and flexibility of this approach, which utilizes the Buchwald–Hartwig cross-coupling reaction, is further underscored by the preparation of several additional aminonaphthalenes in excellent yield, including one that bears a chiral unit.