Mono- and dinuclear cyclopalladates as catalysts for Suzuki–Miyaura cross-coupling reactions in predominantly aqueous media

Suzuki–Miyaura cross-coupling reactions of aryl halides with arylboronic acids were performed in predominantly aqueous media employing two mono- and two dinuclear cyclopalladated complexes as catalysts. These complexes are [Pd(HL)Cl] (I), [Pd(L)(PPh₃)] (II), [Pd₂(μ-dppb)(L)₂] (III) and [Pd₂(μ-dppf)(L)₂] (IV); where H₂L, dppb and dppf represent 4-methoxy-N′-(mesitylidene)benzohydrazide, 1,4-bis(diphenylphosphino)butane and 1,1′-bis(diphenylphosphino)ferrocene, respectively. The reactions were conducted using potassium carbonate as base in presence of tetrabutylammonium bromide (TBAB) at 70/90 °C in dimethylformamide–water (1:20) mixture. Among the four catalysts used, the dinuclear complex IV turned out to be the most effective and afforded moderate to excellent yields with broad substrate scope.     

Palladium-catalysed Suzuki–Miyaura coupling reactions of Bromhexine and Ambroxol

The Suzuki–Miyaura coupling reaction was applied for the synthesis of biologically relevant derivatives of known mucolytic agents Bromhexine and Ambroxol. Using commercially available electron-rich and electron-poor arylboronic acids the desired products are obtained in moderate to high yields (42–81%).     

Palladium catalyzed Mizoroki–Heck and Suzuki–Miyaura reactions using naphthalenomethyl-substituted imidazolidin-2-ylidene ligands in aqueous media

Naphthalenomethyl-substituted imidazolidinium salts (1a-g) were prepared and characterized by conventional spectroscopic methods, ¹H NMR, ¹³C NMR, FTIR, and elemental analysis techniques. The in situ prepared three component systems naphthalenomethyl-substituted imidazolidinium salts, Pd(OAc)₂, and K₂CO₃ catalyzed quantitatively the Mizoroki–Heck and Suzuki–Miyaura coupling of aryl halides under mild conditions in aqueous media.     

Efficient synthesis of neurotrophic honokiol using Suzuki–Miyaura reactions

Efficient synthesis of honokiol (1) was accomplished using two kinds of Suzuki–Miyaura reactions. The first Suzuki–Miyaura reaction was employed to couple 2-bromophenol (6) with 4-hydroxyphenylboronic acid (5), giving rise to biphenol 4, and the second coupling was used to introduce allyl groups at 5- and 3′-positions of honokiol. The total synthesis of 1 was completed in 74% yield over five steps from 6, or in 83% yield over four steps from biphenol 4.     

Synthesis of asymmetric 3,5-diaryl-4H-1,2,6-thiadiazin-4-ones via Suzuki–Miyaura and Stille coupling reactions

Asymmetric 3,5-diaryl substituted 4H-1,2,6-thiadiazin-4-ones can be prepared from 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (1) via a multi-step protocol: selective nucleophilic mono-chloro substitution gives either the mono-methoxy or benzyloxy substituted mono-chlorothiadiazinones that can be phenylated via Suzuki–Miyaura coupling. Subsequent BBr₃ mediated dealkylation gives 3-hydroxy-5-phenyl-4H-1,2,6-thiadiazin-4-one (9) that can be activated by a modified Finkelstein halodehydroxylation via the triflate, enabling further arylation reactions using Suzuki–Miyaura or Stille coupling chemistry.     

A new recyclable/reusable ionic liquid/LiCl system for Suzuki–Miyaura cross coupling reactions

Suzuki–Miyaura cross coupling reactions of aryl halides with aryl boronic acids were carried out in basic ionic liquids in the presence of lithium chloride as a promoter. The coupling reactions, carried out in the absence of base and ligand, proceed in good to excellent yields with easy product isolation and catalyst recycle.     

Chemoselective Suzuki–Miyaura reactions of 4-trifluoromethylsulfonyloxy-6-bromocoumarin

Suzuki–Miyaura reactions of 4-trifluoromethylsulfonyloxy-6-bromocoumarin provide a convenient access to arylated coumarins. The reactions proceed with excellent chemoselectivity in favour of position 4.     

Green and scalable procedure for extremely fast ligandless Suzuki–Miyaura cross-coupling reactions in aqueous IPA using solid-supported Pd in continuous flow

An environmentally friendly continuous-flow protocol for the Suzuki coupling of boronic acids and aryl halides under ligand-free conditions using solid-supported Pd is presented. The process described herein uses very simple reaction conditions and equipment setup and can be readily scaled up to provide multigram quantities of products containing low levels of residual Pd.     

Preparing Pd catalysts based on urea ligand via electrospinning for Suzuki–Miyaura cross-coupling reactions

Pd-catalyzed Suzuki–Miyaura cross-coupling (SMC) reactions are important in chemistry. In this work, using electrospinning technology, we prepared a novel type of composite catalyst with ligand structures such as urea-Pd/PAN (polyacrylonitrile) and used them to catalyze SMC reactions in nontoxic systems and “green” conditions (air atmosphere, low temperature, and short reaction time). This method of preparing hybrid materials is simple and easy to operate. The higher catalytic activity of the catalysts is attributed to active centers with rich electrons transferred from ligands with unique structures, which can decrease the activation energy of the rate-determining step (oxidative addition). In addition, urea-Pd/PAN composite catalysts exhibit higher catalytic performance than those reduced by H₂ because of the smaller size of active species and the more-efficient oxidative addition to Pd⁰–ligand complexes compared to Pd⁰.     

Highly effective activation of aryl chlorides for Suzuki coupling in aqueous media using a ferrocene-based Pd(II)–diimine catalyst

The Suzuki coupling of aryl chlorides with boronic acids using a ferrocene-containing Pd(II)–diimine complex as catalyst, in aqueous media, under microwave heating is reported. A small amount of the catalyst (0.1%) was found to be highly effective for coupling unactivated aryl chlorides with boronic acids to form sterically hindered ortho-substituted biaryls. The same catalyst also enabled the coupling of aryl bromides and iodides with various boronic acids in very high yields. The catalyst is air stable and the catalytic reaction can be completed in 15 min.     

Oxygen-promoted Pd/C-catalyzed Suzuki–Miyaura reaction of potassium aryltrifluoroborates

A simple and highly efficient protocol has been developed for the Pd/C-catalyzed ligand-free Suzuki–Miyaura reaction of potassium aryltrifluoroborates. In this catalytic system, the results demonstrate that oxygen plays a positive role in the cross-coupling reaction. In addition, this catalytic system could be successfully applied to synthesize biaryl compounds containing a carbazole moiety and the catalyst was recycled seven times without significant loss of catalytic activity.     

Chemo-selective Suzuki–Miyaura reactions: Synthesis of highly substituted [1,6]-naphthyridines

The Suzuki-Miyaura reaction of methyl-5-bromo-8-(tosyloxy)-1,6-naphthyridine-7-carboxylate(5),with 2 equiv. of arylboronic acids gave diarylated product, 5,8–diaryl-1,6-naphthyridine-7-carboxylate(7), whereas 1 equiv. of arylboronic acid resulted in site-selective formation of 5-aryl-8-(tosyloxy)-1,6-naphthyridine-7-carboxylate(8). The reactions proceeded with excellent chemo-selectivity in favor of the bromide group. Likewise, one-pot reaction with completely different boronic acids by sequential addition produced 1,6-naphthyridine-7-carboxylates,(10) containing two different aryl groups at 5 and 8 positions.     

Catalytic applications of an organosuperbase dendron grafted on mesoporous SBA-15 and a related palladium complex in Henry and Suzuki–Miyaura coupling reactions

An efficient synthetic method for the synthesis of a basic amine dendron grafted on SBA-15 and a related Pd(II) complex as two novel catalysts has been developed. The prepared catalysts were evaluated in Henry and Suzuki–Miyaura coupling reactions and were found to exhibit excellent heterogeneous catalytic activity in green media, and could be easily separated and reused several times.     

Total Synthesis of (−)-Batrachotoxin Enabled by a Pd/Ag-Promoted Suzuki–Miyaura Coupling Reaction

Batrachotoxin is an extremely potent cardio- and neurotoxic steroidal alkaloid found in certain species of frogs, birds, and beetles. The steroidal 6/6/6/5-membered carbocycle (ABCD-ring) is U-shaped and functionalized with two double bonds, a six-membered C3-hemiacetal across the AB-ring, a seven-membered oxazepane on the CD-ring, and a dimethylpyrrolecarboxy group at the D-ring carbon chain. These structural features present an unusual and formidable synthetic challenge. Herein we report a total synthesis of batrachotoxin based on a newly devised convergent strategy through a 22-step sequence. Enantiopure AB-ring and D-ring fragments were prepared and subjected to a crucial C(sp²)−C(sp²) coupling reaction. Although both C(sp²) centers were sterically encumbered by proximal tetrasubstituted carbon atoms, Ag₂O strongly promoted the Pd(PPh₃)₄-catalyzed Suzuki–Miyaura coupling reaction at room temperature, thereby connecting the two fragments without damaging their preexisting functionalities. Subsequent treatment with t-BuOK induced Dieckmann condensation to cyclize the C-ring. The judiciously optimized functionalizations realized oxazepane formation, carbon chain extension, and pyrrole carboxylic acid condensation to deliver batrachotoxin.     

Suzuki–Miyaura cross-coupling reactions in water using in situ generated palladium(II)–phosphazane complexes

The phosphazane derivatives(L1–3) were readily obtained by reaction of different ratios of PCl3 and PhNH2. The L1–3 derivatives were found to be efficient ligands in the palladium-catalyzed Suzuki C–C coupling reactions in water. It was determined that with the use of L1–3 /Pd(OAc)2 system as a catalyst, aryl halides undergo Suzuki cross-couplings with arylboronic acids to give the desired products in moderate to excellent yields.     

Theoretical study of formation mechanism for 4-methyl-3-phenylbenzonitrile in the course of the Hiyama and Suzuki–Miyaura reactions

A theoretical study on the mechanism of conversion of 3-bromo-4-methylbenzonitrile into 4-methyl-3-phenylbenzo-nitrile in the course of the Suzuki–Miyaura and Hiyama−Denmark cross-coupling reactions has been performed at Cam-B3LYP-D3 level of theory. With the use of Pd–NHC type complex as the catalyst, the Hiyama−Denmark cross-coupling is best suited for this process from both thermodynamic and kinetic aspects.     

Synthesis of EDOT-containing organic dyes via one-pot,four-component Suzuki–Miyaura coupling and the evaluation of their photovoltaic properties

We have developed a one-pot, four-component Suzuki–Miyaura coupling for the synthesis of thiophene-based donor–π-bridge–acceptor (D–π–A) dyes for dye-sensitized solar cells. Two D–π–A dyes, 19 and 20, retaining 3,4-ethylenedioxythiophene (EDOT) beside a cyanoacrylic acid moiety, and one D–π–A dye 21 without EDOT (reference compound) were rapidly synthesized in accordance with the developed procedure. The measurement of the absorption spectra and the electrochemical properties of synthesized dyes, and the photovoltaic properties of solar cells that were prepared using the synthesized dyes 19–21, revealed that the dyes retaining only one EDOT beside a cyanoacrylic acid moiety would exert a high J_sc.