A simple and highly effective oxidative chlorination protocol for the preparation of arenesulfonyl chlorides

2,4-Dichloro-5,5-dimethylhydantoin (DCDMH) was found to be a mild and efficient reagent for the direct oxidative conversion of sulfur compounds to the corresponding arenesulfonyl chlorides in good to excellent yields through oxidative chlorination. The method is suitable for many types of sulfur substrates (thiols, disulfides, and benzylic sulfides). The overall process is simple, practical, and it provides convenient access to a variety of aryl or heteroarylsulfonyl chlorides. The mild reaction conditions and the broad substrate scope render this method attractive and complementary to existing syntheses of aryl or heteroarylsulfonyl chlorides.     

Room temperature Pd(0)/Ad3P-catalyzed coupling reactions of aryl chlorides with bis(pinacolato)diboron

Room temperature Pd(0)/Ad₃P-catalyzed cross-coupling reactions of aryl chlorides with bis(pinacolato)diboron are described. The Pd(0)/Ad₃P catalyst, generated from Ad₃P-coordinated acetanilide-based palladacycle complex, proved to be an efficient catalyst system for the Miyaura borylation reactions of a variety of aryl chlorides with bis(pinacolato)diboron. The mild reaction condition, the easy availability of the catalyst and good coupling yields make these reactions potentially useful in organic synthesis.     

Pd(OAc)2/DABCO-catalyzed Suzuki-Miyaura cross-coupling reaction in DMF

The scope and limitations of the Pd(OAc)₂/DABCO (1,4-diaza-bicyclo[2.2.2]octane)-catalyzed Suzuki-Miyaura cross-coupling reactions have been demonstrated. The results showed that the effect of solvent had a fundamental influence on the reaction. In the presence of Pd(OAc)₂ and DABCO, both aryl bromides and aryl chlorides all worked well with arylboronic acids to form biaryls, heteroaryl-aryls, and biheteroaryls in moderate to excellent yields using DMF as the solvent. Additionally, the reactions of aryl bromides were conducted under relatively mild conditions.     

Electroreductive Radical Borylation of Unactivated (Hetero)Aryl Chlorides Without Light by Using Cumulene-Based Redox Mediators**

Single-electron transfer (SET) plays a critical role in many chemical processes, from organic synthesis to environmental remediation. However, the selective reduction of inert substrates (E_p/2<−2 V vs Fc/Fc⁺), such as ubiquitous electron-neutral and electron-rich (hetero)aryl chlorides, remains a major challenge. Current approaches largely rely on catalyst photoexcitation to reach the necessary deeply reducing potentials or suffer from limited substrate scopes. Herein, we demonstrate that cumulenes–organic molecules with multiple consecutive double bonds–can function as catalytic redox mediators for the electroreductive radical borylation of (hetero)aryl chlorides at relatively mild cathodic potentials (approximately −1.9 V vs. Ag/AgCl) without the need for photoirradiation. Electrochemical, spectroscopic, and computational studies support that step-wise electron transfer from reduced cumulenes to electron-neutral chloroarenes is followed by thermodynamically favorable mesolytic cleavage of the aryl radical anion to generate the desired aryl radical intermediate. Our findings will guide the development of other sustainable, purely electroreductive radical transformations of inert molecules using organic redox mediators.     

Suzuki coupling catalyzed by a homoleptic Pd(I)-Pd(I) solvento complex

The Pd^I-Pd^I bonded complex [Pd₂(CH₃CN)₆][SbF₆]₂ is catalytically active towards Suzuki cross-coupling reactions of aryl bromides or chlorides with various arylboronic acids under mild conditions giving good to excellent yields. Its performance is enhanced by the introduction of stoichiometric or limited phosphines. The effects of different ligands, metal oxidation states [Pd(II), Pd(I) Pd(0)], bases and solvents have been examined.     

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.     

PEG (300)-PdCl2 promoted efficient and convenient Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids

PEG (300) was found as an effective medium for the PdCl₂-catalyzed Suzuki-Miyaura cross-coupling of aryl chlorides with various phenylboronic acids. This cross-coupling pathway conveniently and efficiently gave good to excellent yields of corresponding biaryl nucleus under mild conditions.     

Chemical Transformations of Tetracyclo[3.3.1.1<Superscript>3,7</Superscript>.0<Superscript>1,3</Superscript>]decane (1,3-Dehydroadamantane): VI. Reactions of 1,3-Dehydroadamantane with Carboxylic Acid Chlorides

1,3-Dehydroadamantane reacted with saturated carboxylic acid chlorides to give the corresponding 1-acyl-3-chloroadmantanes as the major products. In some cases, minor products of insertion into the C^α–H bond of acyl chloride were formed. The reactions of 1,3-dehydroadamantane with aromatic (heteroaromatic) carboxylic acid chlorides selectively afforded aryl (hetaryl) 3-chloroadamantan-1-yl ketones. The described reactions provide a synthetic route to difficultly accessible alkyl (aryl) ketones containing a 3-chloroadamantan- 1-yl group in one step under mild conditions with high yields.     

Silica-Supported Phosphine Palladium(0) Complex Catalyzed Phenylation of Acid Chlorides and Aryl Iodides by Sodium Tetraphenylborate

In the presence of a catalytic amount of silica – supported phosphine palladium(0) complex, sodium tetraphenylborate (NaBPh₄) reacts with acid chlorides under mild conditions to give the corresponding phenyl ketones in 57 – 80% yields; it also reacts with aryl iodides to afford the corresponding biaryls in 75 – 84% yields.     

Pd/Cu bimetallic co-catalyzed direct 2-arylation of benzoxazole with aryl chloride

An efficient Palladium/Copper bimetallic co-catalyzed direct 2-arylation of benzoxazoles with aryl chlorides is presented. The Pd(OAc)₂/CuI/NiXantphos-based catalyst enables the installation of various aryl and heteroaryl groups in good to excellent yields (75–99%). Preliminary mechanism investigation indicates that Pd/Nixantphos complex activates C-Cl bond of aryl chlorides via oxidative addition, and Cu/Nixantphos complex chelates with nitrogen atom to lower the pK_a of the 2-H in benzoxazoles.     

Highly efficient Pd‐PEPPSI‐IPr catalyst for N‐(4‐pyridazinyl)‐bridged bicyclic sulfonamides via Suzuki–Miyaura coupling reaction

A protocol for the Suzuki–Miyaura coupling of novel 2‐(6‐chloropyridazin‐3‐yl)‐5‐(aryl/heteroarylsulfonyl)‐2,5‐diazabicyclo[2.2.1]heptanes and heteroarylboronic acids to afford variety of coupled products was realized. Pd‐PEPPSI‐IPr catalyst was found to be a powerful and reusable catalyst under relatively mild reaction conditions.     

Ligand-supported palladium-catalyzed cross-coupling reactions of (hetero) aryl chlorides

The introduction of electron rich and sterically hindered ligands has made otherwise inert aryl chlorides and hetero aryl chlorides viable coupling partners in palladium-catalyzed Suzuki-Miyaura, Sonogashira, Stille and other types of cross-coupling reactions. This review gives highlights of cross-coupling of aryl chlorides employing in situ generated palladium catalytic systems.     

X-ray structure of trans-chloro(1-naphthyl) bis(triphenylphosphine)nickel(II) and its application for catalytic dehalogenation of aryl chlorides

X-ray structure of trans-chloro(1-naphthyl)bis(triphenylphosphine)nickel(II) (4) was determined. The complex crystallizes in the triclinic system, space group P 1 with a = 12.0623(3), b = 13.8844(4), c = 14.5261(4) Å, α = 104.787(2), β = 104.861(2), γ = 107.602(2)°, and Z = 2. Dehalogenation of aryl chlorides was successfully performed in isopropyl alcohol (IPA) by using 4 as a precatalyst in the absence of reducing agent. The dehalogenation proceeded smoothly at ambient temperature to provide desired arenes in almost quantitative yields.     

Selective palladium-catalyzed arylation(s) of benzaldehyde derivatives by N-heterocarbene ligands

The 2- or 2,6-position(s) of aromatic aldehydes were directly and selectively arylated with aryl chlorides or bromides in the presence of a catalytic system prepared in situ from Pd(OAc)₂, imidazolinium chlorides (1-5) and Cs₂CO₃.     

AlAr3(THF): highly efficient reagents for cross-couplings with aryl bromides and chlorides catalyzed by the economic palladium complex of PCy3

Novel and highly efficient cross couplings of aryl bromides and chlorides with AlAr3(THF) (Ar = Ph, 2,4,6-Me3C6H2, 2-naphthyl or 4-Me3SiC6H4) catalyzed by the economic palladium catalyst of PCy3 are reported without the use of a base and under mild reaction conditions at room temperature or temperatures < or = 60 degrees C even for couplings of bulky aryl halides and the Al(2,4,6-Me3C6H2)3(THF) reagent.     

A highly active palladium(II)–bis(oxazoline) catalyst for Suzuki–Miyaura,Mizoroki–Heck and sonogashira coupling reactions in aqueous dimethylformamide

An efficient catalytic system based on a new palladium–bis(oxazoline) ( Pd-BOX-1 ) complex has been developed. The complex Pd-BOX-1 adopts a legless chair‐type structure where the distorted square planar [PdN₂Cl₂] moiety and the benzene ring spacer represent the seat and the chair back, respectively. The catalytic activity of Pd-BOX-1 has been investigated in dimethylformamide–water under aerobic and mild conditions in Suzuki–Miyaura coupling reactions of arylboronic acids with aryl iodides, aryl bromides and aryl chlorides, Mizoroki–Heck coupling reactions of aryl halides with styrene derivatives, and Sonogashira coupling reactions of aryl halides with terminal alkynes. A wide range of functional groups as substituents on the arylboronic acids and aryl halides were considered. Pd-BOX-1 demonstrates exceptional air and moisture stability. Of note, the catalyst system based on Pd-BOX-1 shows high recycling ability in Suzuki–Miyaura coupling reactions in dimethylformamide–water without any loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Difluoro(aryl)(perfluoroalkyl)‐λ4‐sulfanes and Selanes: Missing Links of Trichloroisocyanuric Acid/Potassium Fluoride Chemistry

The TCICA/KF approach to oxidative fluorination of heteroatoms has emerged as a surprisingly simple, safe, and versatile surrogate to classically challenging fluorination reactions. Although polyfluorination (or chlorofluorination) of diaryl disulfides, diaryl diselenides, diaryl ditellurides, aryl iodides, and aryl(perfluoroalkyl)tellanes has been described, the application of this TCICA/KF methodology to aryl(perfluoroalkyl)sulfanes and selanes remains an area of unexplored chemical space. Accordingly, to address the “missing links” in the developing series of chalcogen‐based substrate reactivity, we report mild syntheses of metastable difluoro(aryl)(perfluoroalkyl)‐λ⁴‐sulfanes and selanes. As only limited examples of these species exist in the current literature (accessible only by using F₂ or XeF₂/HF), we have carried out detailed structural analyses, primarily using NMR and SC‐XRD data. In addition, we investigate the effect of the perfluoroalkyl chain on the outcome of oxidative fluorination, and, finally, we provide preliminary evidence that difluoro(aryl)(trifluoro‐methyl)‐λ⁴‐sulfanes may act as fluorinating reagents.     

Palladium(II)‐N‐heterocyclic carbene complexes: synthesis,characterization and catalytic application

N‐Heterocyclic carbenes (NHCs) are of great importance and are powerful ligands for transition metals. A new series of sterically hindered benzimidazole‐based NHC ligands (LHX) ( 2a , 2b , 2c , 2d , 2e , 2f ), silver–NHC complexes ( 3a , 3b , 3c , 3d , 3e , 3f ) and palladium–NHC complexes ( 4a , 4b , 4c , 4d , 4e , 4f ) have been synthesized and characterized using appropriate spectroscopic techniques. Studies have focused on the development of a more efficient catalytic system for the Suzuki coupling reaction of aryl chlorides. Catalytic performance of Pd–NHC complexes and in situ prepared Pd(OAc)₂/LHX catalysts has been investigated for the Suzuki cross‐coupling reaction under mild reaction conditions in aqueous N,N‐dimethylformamide (DMF). These complexes smoothly catalyzed the Suzuki–Miyaura reactions of electron‐rich and electron‐poor aryl chlorides. Copyright © 2014 John Wiley & Sons, Ltd.     

Ascorbic Acid as an Aryl Radical Inducer in the Gold-Mediated Arylation of Indoles with Aryldiazonium Chlorides

In recent years interest in the development of protocols that facilitate the oxidative addition of gold to access mild cross-coupling processes mediated by this metal has increased. In this context, we report herein that ascorbic acid, a natural and readily accessible antioxidant, can be used to accelerate the oxidative addition of aryldiazonium chlorides onto Au^I. The aryl–Au^III species generated in this way, has been used to prepare 3-arylindoles in a one-pot protocol starting from anilines and para-, meta-, and ortho- substituted aryldiazonium chlorides. The mechanism underlying the oxidative addition has been examined in detail based on EPR analyses, cyclic voltammetry, and DFT calculations. Interestingly, we have found that in this protocol, the chloride atom induces the Au^II/Au^III oxidation step.     

Nickel(II)-aryl complexes as catalysts for the Suzuki cross-coupling reaction of chloroarenes and arylboronic acids

A series of air- and moisture-stable Ni(II)-(σ-aryl) complexes, Ni(PPh₃)₂(aryl)X (X = Cl, Br), were employed as catalyst precursors in the Ni-catalyzed Suzuki cross-coupling reaction. These pre-catalysts easily form the catalytically active Ni(0) species in situ without the need of additional reducing agents. A general catalytic system involving Ni(PPh₃)₂(1-naph)Cl and PPh₃ proved to be highly effective for the Suzuki reaction of aryl chlorides under mild conditions (at 60 °C in THF in the presence of K₂CO₃ as the base).