Negishi Coupling Research Articles

Negishi coupling reactions with [11C]CH3I: a versatile method for efficient 11C-C bond formation.

Herein, we present a fast, efficient and general one-pot method for the synthesis of 11C-labelled compounds via the Negishi cross-coupling reaction. Our approach, based on the in situ formation of [11C]CH3ZnI and subsequent reaction with aryl halides or triflates, has proven efficient to synthesize [11C]thymidine, a biologically relevant compound with potential applications as a proliferation marker. Theoretical calculations have shown irreversible formation of a tetracoordinated nucleophilic 11C-Zn(ii) reagent and electronic requirements for an efficient Negishi coupling.

Palladium-catalysed coupling of α-halo vinylphosphonate and α-phosphonovinyl sulfonate with alkylzincs: straightforward and versatile synthesis of α-alkyl vinylphosphonates

Easy and efficient access to α-alkylated vinylphosphonates via Pd-catalysed Negishi coupling!

A Scalable Route for the Regio- and Enantioselective Preparation of a Tetrazole Prodrug: Application to the Multi-Gram-Scale Synthesis of a PCSK9 Inhibitor

The synthesis of multigram quantities of small molecule PCSK9 inhibitor (R,S)-3 is described. The route features a safe, multikilogram method to prepare 5-(4-iodo-1-methyl-1H-pyrazol-5-yl)-2H-tetrazole (10). A three-component dynamic kinetic resolution between tetrazole 10, acetaldehyde, and isobutyric anhydride was catalyzed by a chiral DMAP catalyst to afford enantiomerically enriched hemiaminal ester (S)-12 on multikilogram scale. Magnesiation, transmetalation, and Negishi coupling provided access to Boc-intermediate (R,S)-13, which was deprotected to provide (R,S)-3 in multigram quantities.

Progress towards the total synthesis of hamigerans C and D: a direct approach to an elaborated 6-7-5 carbocyclic core.

The hamigeran family of natural products has been the target of numerous synthetic efforts due to its biological activity and interesting structural properties. Herein we disclose our efforts toward the synthesis of hamigerans C and D, unique among the initially isolated members due to their 6-7-5 carbocyclic core. Our approach directly targets this tricyclic motif by sequential Negishi and Heck coupling reactions, yielding an advanced intermediate with all necessary carbons and sufficient functionality poised for completion of the synthesis of these two natural products.

Palladium-Catalyzed Negishi Coupling of α-CF3 Oxiranyl Zincate: Access to Chiral CF3-Substituted Benzylic Tertiary Alcohols.

We report a Pd-catalyzed stereospecific α-arylation of optically pure 2,3-epoxy-1,1,1-trifluoropropane (TFPO). This method allows for the direct and reliable preparation of optically pure 2-CF3-2-(hetero)aryloxiranes, which are precursors to many CF3-substituted tertiary alcohols. The use of continuous-flow methods has allowed the deprotonation of TFPO and subsequent zincation at higher temperature compared to that under traditional batch conditions.

A Combined Experimental/Computational Study of the Mechanism of a Palladium-Catalyzed Bora-Negishi Reaction.

Experimental and computational efforts are reported which illuminate the mechanism of a novel boron version of the widespread Negishi coupling reaction that offers a new protocol for the formation of aryl/acyl C-B bonds using a bulky boryl fragment. The role of nucleophilic borylzinc reagents in the reduction of the PdII pre-catalysts to Pd0 active species has been demonstrated. The non-innocent behavior of the PPh3 ligands of the [Pd(PPh3 )2 Cl2 ] pre-catalyst under activation conditions has been probed both experimentally and computationally, revealing the formation of a trimetallic Pd species bearing bridging phosphide (PPh2- ) ligands. Our studies also reveal the monoligated formulation of the Pd0 active species, which led us to synthesize related (η3 -indenyl)Pd-monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.

Access to (Hetero)arylated Selenophenes via Palladium‐catalysed Stille, Negishi or Suzuki Couplings or C−H Bond Functionalization Reaction

Abstract(Hetero)aryl‐substituted selenophenes exhibit important physical properties especially for optoelectronics. Palladium‐catalysed coupling reactions currently represent the most efficient methods to prepare such (hetero)arylated selenophene derivatives. Initially, Stille coupling was the most efficient reaction for the synthesis of these compounds; however, over the last decade, Suzuki coupling has become the most commonly employed. Recently, Pd‐catalysed arylation via the C−H bond activation of selenophenes has proved to be a very convenient alternative method for the preparation of several arylated selenophenes as there is no need to prepare organometallic derivatives. In this Review, the progress and substrate scope in the synthesis of both C2‐ and C3‐arylated selenophenes via Pd‐catalysis are summarized.

Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes.

A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar1 CH2 (HOCH2 )C=C(CH2 OH)I (Ar1 =Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH2 )C=C(CH2 OH)I, accessed from ultra-low cost HOCH2 C≡CCH2 OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar1 CH2 (HOCH2 )C=C(CH2 OH)CH2 Ar2 (Ar2 =Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar1 CH2 (CHO)C=C(CHO)CH2 Ar2 , which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.

Speciation of ZnMe2, ZnMeCl, and ZnCl2 in Tetrahydrofuran (THF), and Its Influence on Mechanism Calculations of Catalytic Processes

This paper examines the speciation of ZnMe2, ZnMeCl, and ZnCl2 in tetrahydrofuran (THF) solution, and provides experimental (infrared (IR) and calorimetric experiments) and density functional theory (DFT) data to conclude that the species in THF solution are, beyond a doubt, ZnMe2(THF)2, ZnMeCl(THF)2, and ZnCl2(THF)2. Consequently, coordinated THF should be used in DFT mechanistic calculations (e.g., Negishi reactions in THF). Naked or single THF coordinated molecules are virtually nonexistent in THF solutions. A cluster-continuum model for the solvent is recommended to obtain a more-correct representation. The presence or absence of THF produces a marked effect on the thermodynamics of the Negishi catalysis and a lesser effect on the kinetics of the transmetalation.

Regioselective Bromination of Benzocycloheptadienones for the Synthesis of Substituted 3,4-Benzotropolones Including Goupiolone A.

Type-18 or -23 benzocycloheptadienones are readily prepared by ring-closing olefin metatheses. Adding Br2 to 23 and eliminating HBr gave the bromoolefin 28 using DBU or its isomer iso-28 using DABCO, both with near-perfect regiocontrol. Both 28 and iso-28 underwent Sonogashira, Suzuki, Negishi, and Heck couplings as well as Pd-catalyzed alkoxycarbonylations. Hydrolysis of the resulting α-ketoketals and enolization of the liberated α-diketones delivered a portfolio of hitherto unknown 3,4-benzotropolones. The 8-ethoxycarbonylated dimethyl-3,4-benzotropolone 50 obtained by this route was dimethylated to give goupiolone A (52). This synthesis encompasses 9 steps from 22, that is, half as many as the only previous synthesis (19 steps). A variant of our route afforded the 1,8-dibromide 54. Coupling with excess phenylboronic acid and ketal hydrolysis provided the diphenylated benzotropolone 56 and suggests a strategy, by which the natural bispulvinone aurantricholone (7) might be reached.

A Heterobimetallic Pd–Zn Complex: Study of a d8–d10Bond in Solid State, in Solution, and in Silico

A heterobimetallic Pd(II)–Zn(II) complex has been prepared and characterized by X-ray diffraction analysis. An accompanying computational study shows that the bimetallic complex is predominantly stabilized by a short metal–metal bond; ΔG for the reversible dissociation of that bond in solution could be quantified by NMR-titration experiments. A comparison of the experimental crystal structure with previously calculated structures of intermediates and transition states for transmetalation in the Negishi coupling reveals close similarity.

Synthesis and Cytostatic and Antiviral Profiling of Thieno-Fused 7-Deazapurine Ribonucleosides

Two isomeric series of new thieno-fused 7-deazapurine ribonucleosides (derived from 4-substituted thieno[2',3':4,5]pyrrolo[2,3-d]pyrimidines and thieno[3',2':4,5]pyrrolo[2,3-d]pyrimidines) were synthesized by a sequence involving Negishi coupling of 4,6-dichloropyrimidine with iodothiophenes, nucleophilic azidation, and cyclization of tetrazolopyrimidines, followed by glycosylation and cross-couplings or nucleophilic substitutions at position 4. Most nucleosides (from both isomeric series) exerted low micromolar or submicromolar in vitro cytostatic activities against a broad panel of cancer and leukemia cell lines and some antiviral activity against HCV. The most active were the 6-methoxy, 6-methylsulfanyl, and 6-methyl derivatives, which were highly active to cancer cells and less toxic or nontoxic to fibroblasts.

Alkyl−(Hetero)Aryl Bond Formation via Decarboxylative Cross‐Coupling: A Systematic Analysis

AbstractSuzuki, Negishi, and Kumada couplings are some of the most important reactions for the formation of skeletal C−C linkages. Their widespread use to forge bonds between two aromatic rings has enabled every branch of chemical science. The analogous union between alkyl halides and metallated aryl systems has not been as widely employed due to the lack of commercially available halide building blocks. Redox‐active esters have recently emerged as useful surrogates for alkyl halides in cross‐coupling chemistry. Such esters are easily accessible through reactions between ubiquitous carboxylic acids and coupling agents widely used in amide bond formation. This article features an amalgamation of in‐house experience bolstered by approximately 200 systematically designed experiments to accelerate the selection of ideal reaction conditions and activating agents for the cross‐coupling of primary, secondary, and tertiary alkyl carboxylic acids with both aryl and heteroaryl organometallic species.

Alkyl-(Hetero)Aryl Bond Formation via Decarboxylative Cross-Coupling: A Systematic Analysis.

Suzuki, Negishi, and Kumada couplings are some of the most important reactions for the formation of skeletal C-C linkages. Their widespread use to forge bonds between two aromatic rings has enabled every branch of chemical science. The analogous union between alkyl halides and metallated aryl systems has not been as widely employed due to the lack of commercially available halide building blocks. Redox-active esters have recently emerged as useful surrogates for alkyl halides in cross-coupling chemistry. Such esters are easily accessible through reactions between ubiquitous carboxylic acids and coupling agents widely used in amide bond formation. This article features an amalgamation of in-house experience bolstered by approximately 200 systematically designed experiments to accelerate the selection of ideal reaction conditions and activating agents for the cross-coupling of primary, secondary, and tertiary alkyl carboxylic acids with both aryl and heteroaryl organometallic species.

Benzoxazole-Directed Halogen Dance of Bromofuran

A halogen dance of a benzoxazole-conjugated bromofuran derived from furfural is described. The reaction proceeds through a benzoxazole-directed lithiation to provide the α-lithiofuran, which is subjected to Negishi coupling to give α-arylated benzoxazole-conjugated furan derivatives. The synthetic utility of the reaction was demonstrated by transformation of the residual bromo group into a side chain bearing a siloxane moiety, which resulted in a significant improvement in solubility in organic solvents.

Synthesis and Physicochemical Properties of Piceno[4,3-b:9,10-b']dithiophene Derivatives and Their Application in Organic Field-Effect Transistors.

Efficient synthesis and characterization of several piceno[4,3-b:9,10-b′]dithiophene (PiDT) derivatives by Negishi coupling, epoxidation, and Lewis acid-catalyzed cycloaromatization sequences and their potential utility in organic field-effect transistors (OFETs) have been reported. PiDT derivatives, with extended π-electron systems, showed high air stability due to their deep highest occupied molecular orbital energy levels (around −5.6 eV). OFET devices based on 2,11-dioctylated PiDT (C8-PiDT) showed excellent hole mobility, as high as 2.36 cm2 V–1 s–1. Their structure–property relationships were investigated by X-ray diffraction and atomic force microscopy.

Breaking Amides using Nickel Catalysis.

Amides have been widely studied for decades, but their synthetic utility has remained limited in reactions that proceed with rupture of the amide C-N bond. Using Ni catalysis, we have found that amides can now be strategically employed in several important transformations: esterification, transamidation, Suzuki-Miyaura couplings, and Negishi couplings. These methodologies provide exciting new tools to build C-heteroatom and C-C bonds using an unconventional reactant (i.e., the amide), which is ideally suited for use in multi-step synthesis. It is expected that the area of amide C-N bond activation using nonprecious metals will continue to flourish and, in turn, will promote the growing use of amides as synthons in organic synthesis.

Formation of (PNP)Rh complexes containing covalent rhodium-zinc bonds in studies of potential Rh-catalysed Negishi coupling.

While investigating rhodium-catalyzed Negishi coupling, it was observed that the (PNP)Rh fragment readily inserted into zinc-carbon bonds to form isolable molecules with covalent rhodium-zinc bonds.

ChemInform Abstract: Solution to the C3—Arylation of Indazoles: Development of a Scalable Method.

AbstractThe title transformation is achieved following a Negishi coupling protocol which tolerates variously functionalized aryl and hetaryl bromides.

Inter-Metallocene Cross-Coupling Reaction and Oxidation Study on Hetero Nuclear Bimetallocene Compounds including Fe, Ru and Os

Abstract Hetero nuclear bimetallocene compounds, ferrocenylruthenocene (FcRc), ferrocenylosmocene (FcOc), ruthenocenylosmocene (RcOc) and 1-ferrocenyl-4-ruthencoenylbenzene (FcPhRc) were synthesized by Suzuki–Miyaura coupling or Negishi coupling reaction. When these compounds were oxidized with I2, mixed-valence compounds, [(C5H5)FeII(C5H4-C5H4)OsIV-I(C5H5)]I3 (1), [(C5H5)RuII(C5H4-C5H4)OsIV-I(C5H5)]I3 (3) and [(C5H5)FeIII(C5H4-Ph-C5H4)RuIV-I(C5H5)](I3)2 (4), were obtained. The valence state was investigated by using 57Fe Mössbauer spectroscopy and variable-temperature 1H NMR spectroscopy. FcOc was also oxidized by [(C5H5)2RuIV-Cl]PF6, and the ferrocenylosmocenium-Cl adduct [(C5H5)FeII(C5H4-C5H4)OsIV-Cl(C5H5)]PF6 (2) was obtained. The valence detrapping described as FeII-OsIV$ \rightleftharpoons $ FeIII-OsIII was observed by 1H NMR measurement in high-temperature solution. The valence detrapping was also observed in solid state by 57Fe Mössbauer spectroscopy.