Coupling Reaction of Organoboronic Acids with Chloropyrimidines and Trichlorotriazine

Pd-catalyzed cross-coupling reactions of chloropyrimidirtes with alkenylboronic acids readily proceed to give the corresponding alkenylpyrimidines in high to excellent yields. The coupling reaction of 2,4-dichloropyrimidine or 2,4,6-trichloropyrimidine with one equivalent of alkenylboronic acid occurred more easily on 4-position than on 2-position, which implied that the reaction is highly regioselective. The reaction is stereospecific since the configuration of C=C remained intact. The preliminary study on the cross-coupling reactions of 2,4,6-trichlorotriazine with one equivalent of arylboronic acids showed that the reactions afforded the monosubstituted triazines in moderate yields. The effect of steric hindrance of the substitutents on the reactions was found.     

Microwave-Assisted Cross-Coupling Reaction of Sodium Tetraphenylboratewith Carboxylic Anhydrides Catalyzed by Palladium

Cross-coupling processes of aryl or alkenyl halides with organometallic compounds of main group elements cat alyzed by palladium complexes have been found extensive use in organic synthesis. These cross-coupling reactions offer a powerful tool for the formation of carbon-carbon bonds. [1] The Suzuki-Miyaura cross-coupling reaction has been employed for the synthesis of ketone as well.     

New progress in theoretical studies on palladium-catalyzed C−C bond-forming reaction mechanisms

This review reports a series of mechanistic studies on Pd-catalyzed C-C cross-coupling reactions via density functional theory(DFT) calculations.A brief introduction of fundamental steps involved in these reactions is given,including oxidative addition,transmetallation and reductive elimination.We aim to provide an important review of recent progress on theoretical studies of palladium-catalyzed carbon-carbon cross-coupling reactions,including the C-C bond formation via C-H bond activation,decarboxylation,Pd(Ⅱ)/Pd(Ⅳ) catalytic cycle and double palladiums catalysis.     

Microwave-promoted Palladium Catalyzed Suzuki Cross-coupling Reaction in Water

Suzuki coupling is probably the most versatile approach among the cross-coupling reactions and the reaction has long been the subject of intensive work in the area of transition-metal chemistry1. In recent years, various modifications involving the catalyst, solvents, bases, reaction conditions and synthetic technique have been developed 2. The Suzuki cross-coupling reaction in water is more safe, economical. It is an environmentally friendly alternative in organic synthesis. The use of w…     

Stereoselective Synthesis of Novel C-Disaccharides via Suzuki Cross-Coupling Reaction

Novel β-C-disaccharides containing a three carbon linkage using exo-glycal as the precursor were prepared stereoselectively. The synthesis was achieved by the tandem reactions of the stereoselective hydroboration of exo-glycal and Suzuki cross-coupling reaction with an iodovinyl sugar, and followed by hydrogenated deprotection under the catalysis of Pd（OH）2/C.     

Mechanism and origin of diastereoselectivity of N-heterocyclic carbene-catalyzed cross-benzoin reaction: A DFT study

Herein,the origin of the diastereoselectivity of N-heterocyclic carbene(NHC)-catalyzed cross-benzoin reactions between an a-amino aldehyde and furfural was studied by density functional theory.The computational results showed that the reaction proceeded through four steps:nucleophilic addition of NHC onto furfural,formation of a Breslow intermediate,cross-coupling reaction between Breslow intermediate and a-amino alde hyde,and dissociation of the catalyst.The cross-coupling was identified as the diaste reoselectivity-determining step,with the R-configured product generated preferentially.Noncovalent inte raction(NCI)analysis showed that the C-H…O and C-H…F inte ractions were responsible for determining the diastereoselectivity.     

Synthesis and photophysical properties of poly(aryleneethynylene)s containing dibenzosilole unit

A series of poly(aryleneethynylene)s containing dibenzosilole unit has been synthesized by palladium-catalyzed Sonogashira cross-coupling reactions with 2,7-diethynyl-9,9-dihexyl-3,6-dimethoxy-9H-dibenzosilole(4) as the key monomer.Their photophysical properties in solution were investigated.All of the polymers showed intense fluorescence with high quantum efficiencies.     

Decarbonylative C-C bond forming reactions mediated by transition metals

New methods for carbon-carbon (C-C) forming reactions are constantly emerging in the field of organic synthesis. In this review, a brief history followed by recent developments of decarbonylative C-C forming reactions mediated by transition metals is described. Many different substrates are presented and the review is organized by the different carbonyl precursors, such as acyl chlorides, aldehydes, anhydrides, esters and ketones, used in the respective transformations. Furthermore, the broad scope of these reactions is exhibited by the application to several reaction types (e.g. Heck-type reactions, Suzuki cross-coupling type reactions, C-H activation, etc.) as well as a natural product synthesis (e.g. muscroride A). While several examples are provided, this review marks the beginning of a new field that is still in its infancy and for what might be a new approach to achieve highly efficient reactions that come closer to meeting the standards of chemical economies (e.g. atom, redox, step, etc.) and green chemistry.     

Recent advances in theoretical studies on ligand-controlled selectivity of nickel-and palladium-catalyzed cross-coupling reactions

Nickel-and palladium-catalyzed cross-coupling reactions have attracted wide attentions,while ligandcontrolled selectivity in these reactions are still elusive,and calculations can help obtain possible catalytic cycles to generate different products and provide insights into key factors of selectivity,which facilitates the development of new catalyst systems to control reaction selectivity.This review covers our efforts and some significant achievements from other groups on ligand-controlled reaction selectivity of coupling reactions,including introduction,computational methods,selectivity control by ligands in Niand Pd-catalyzed coupling reactions,as well as summary and future perspectives.     

Recent catalytic syntheses of trifluoromethylthio-containing organic compounds by transition metals,chiral organocatalysts,and photocatalysts

This review summarizes the recent advances in the catalytic syntheses of CF_3S-containing organic molecules using various nucleophilic or electrophilic trifluoromethylthiolating reagents.C-halogen and C—H bonds in various molecules have been transformed to C—SCF_3 bonds by transition-metal-catalyzed reactions,such as cross-coupling of aryl halides.Enantioselective reactions controlled by chiral metal complexes or chiral organocatalysts have afforded many trifluoromethylthiolated chiral architectures,such as β-ketoesters and oxindoles.Very recently,visible-light-induced photoredox trifluoromethylthiolations have been developed,providing versatile CF_3S-containing structures efficiently.     

The role of Cul in the siloxane-mediated Pd-catalyzed cross-coupling reactions of aryl iodides with aryl lithium reagents

Experiments indicate that a catalytic amount of Cul plays an important role in the siloxane-mediated Pd-catalyzed cross-coupling reactions with the direct use of organolithium reagents.Addition of organolithium to the siloxane transfer agent generates an organosilicon intermediate.DFT calculations indicate that Cul initially accelerates the Si-Pd(Ⅱ) transmetalation of the organosilicon intermediate by the formation of CuI₂^-.Subsequently,CuI₂^-works as a shuttle between the Si-Cu(Ⅰ) and Cu(Ⅰ)-Pd(Ⅱ)transmetalation processes.     

SYNTHESIS OF FUNCTIONAL MACROMOLECULE INTERMEDIATE THROUGH COUPLING REACTION CATALYZED BY [bmim]Cl/FeCl_3 IONIC LIQUID

1. INTRODUCTION The coupling reactions of aromatic compounds have important application in both laboratory work and industry processes such as in organic synthesis, dye preparation and pesticide produce, especially in special medicament exploiture. Since the cross-coupling reaction between Grignard agent and arylic halide catalyzed by complex compound of nickel and phosphorus was reported by Corriu and Kumada in 1972, various coupling reactions have been developed [1~4]. These coupling r…     

Effect of flexible units on the properties of silicon-containing phenyleneethynylene hybrid oligomers

New silicon-containing phenyleneethynylene hybrid oligomers P2, P3, and P4 were synthesized via Sonogashira cross-coupling reactions of ethynyl-terminated silazane monomer N,N′-bis(4-ethynylphenyl)-1,1-diphenylsilazane(M1) and corresponding bis-(4-bromo-phenyl)-ended organosilicon unit containing monomers, respectively. These new oligomers were easily soluble in common solvents. The incorporation of flexible organosilicon units in the oligomers leads to blue-shift in both the UV-Vis absorption and fluorescence emission spectra similarly. The results of differential scanning calorimetry(DSC) indicate that the flexible units relieve the rigidity of oligomeric chain and provide favorable conformation for thermal cross-linking reactions. The oligomers show good thermal and thermal-oxidative stability from the thermogravimetric analysis(TGA), with their decomposition temperature at 10% weight loss(T10%) higher than 400 ?C under both nitrogen and air atmosphere.     

Induction heating enables efficient heterogeneous catalytic reactions over superparamagnetic nanocatalysts

Most catalytic processes are achieved by heating the whole reaction systems including the entire reactor,substrate and solvent, which leads to energy loss and obvious heat transfer limits. In this study, induction heating was employed to boost the catalytic Suzuki-Miyaura cross-coupling reactions by using conductive superparamagnetic microspheres with loaded Pd nanoparticles as heterogeneous catalysts. It was found that, at the same apparent reaction temperatures, the reactions by adopting the i...     

Silica-supported Copper（Ⅱ） Catalyzed Coupling of Arylboronic Acids with Imidazoles

Immobilized copper（Ⅱ） in organic-inorganic hybrid materials catalyzed Ar-N coupling of arylboronic acids with imidazoles has been developed. Arylboronic acids reacted with imidazoles smoothly in the presence of a 3-（2-aminoethylamino）propyl functionalized silica gel immobilized copper（Ⅱ） catalyst （10 mol%） in methanol without any additives and bases. The reactions generated the corresponding cross-coupling products in good yields. Furthermore, silica-supported copper can be recovered and recycled by a simple filtration procedure and used for five consecutive trials without decreases in activity.     

DFT Investigation on the Mechanism of Pd（0） Catalyzed Sonogashira Coupling Reaction

Based on DFT calculations, the catalytic mechanism of palladium(0) atom, commonly considered as the catalytic center for Sonogashira cross-coupling reactions, has been analyzed in this study. In the cross-coupling reaction of iodobenzene with phenylacetylene without co-catalysts and bases involved, mechanistically plausible catalytic cycles have been computationally identified. These catalytic cycles typically occur in three stages: 1) oxidative addition of an iodobenzene to the Pd(0) atom, 2) reaction of the product of oxidative addition with phenylacetylene to generate an intermediate with the Csp bound to palladium, and 3) reductive elimination to couple the phenyl group with the phenylethynyl group and to regenerate the Pd(0) atom. The calculations show that the first stage gives rise to a two-coordinate palladium (Ⅱ) intermediate (ArPdI). Starting from this intermediate, the second oxidative stage, in which the C–H bond of acetylene adds to Pd(Ⅱ) without co-catalyst involved, is called alkynylation instead of transmetalation and proceeds in two steps. Stage 3 of reductive elimination of diphenylacetylene is energetically favorable. The results demonstrate that stage 2 requires the highest activation energy in the whole catalysis cycle and is the most difficult to happen, where co-catalysts help to carry out Sonogashira coupling reaction smoothly.     

Tailoring the photophysical and photovoltaic properties of boron-difluorodipyrromethene dimers

Five boron-difluorodipyrromethene(BODIPY) dimers have been designed and synthesized successfully via acid-catalysed condensation and Pd-catalysed cross-coupling reactions.The structural modification,including verifying the structures of the π-bridges,altering the positions the bridges link(meso-or β-positions),and regulating the molecular planarity,can modulate the photophysical properties and the aggregation behaviors of the five dimers efficiently.Solution-processed organic solar cells were fabricated to evaluate the photovoltaic properties of these molecules further either as acceptors or donors.When using as nonfullerene acceptor and blended with the polymer donor of PTB7,an opencircuit voltaic(V_(oc)) of 1.12 and 1.08 V was achieved from the thiophene and benzodithiophene bridged BODIPY dimers,respectively.This V_(oc) is among the top values achieved from the non-fullerene organic solar cells so far.     

Stereoselective Synthesis of C-Glycosides by Suzuki Cross-coupling Reaction

Carbohydrates and their conjugates have been recognized to play a wide variety of metabolic roles in numerous biological processes.[1] Various modified sugars and analogues have been recently synthesized for further investigation of glycosidase reactions and for the development of specific glycosidase inhibitors.[2] As one of the most important carbohydrate mimics, C-glycosides have attracted great attention due to their stability to chemical or enzymatic hydrolysis of the glycosidic linkage. A number of methodologies for the preparation of C-glycosides have been extensively investigated.[3] We have recently reported the syntheses of novel C-glycosyl amino acids and amino-C-disaccharides possessing a ketose form via the stereoselective 1,3-dipolar cycloaddition of exo-methylenesugars (1) and nitrones.[4,5] As a continuation of our research on the synthesis of C-glycosides using exo-methylenesugar as the precursor, we wish to describe here a stereoselective synthesis of C-glycosides by Suzuki cross-coupling reaction.     

N-Doped porous carbon supported palladium nanoparticles as a highly efficient and recyclable catalyst for the Suzuki coupling reaction

A new catalyst, Pd particles supported on the N-doped porous carbon(PC) derived from Zn-based metal–organic frameworks(zeolitic imidazolate framework: ZIF-8), was successfully prepared for the first time.The as-prepared catalyst was designated as N-doped PC-Pd, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscope, N_2 adsorption and inductively coupled plasma atomic emission spectroscopy. The N-doped PC-Pd composite exhibited high catalytic activity toward the Suzuki–Miyaura cross-coupling reactions. The yields of the products were in the range of 90%–99%. The catalyst could be readily recycled and reused at least 6 consecutive cycles without a significant loss of its catalytic activity.     

A Simple Synthesis of dl—Shikonin

A new facile route for the synthesis of dl-shikomin is presented.Reformatsky reaction assisted cross-coupling of 1,4,5,8-tertramethoxynaphthalene-2-carbaldehyde and ethyl-bromoacetate was empolyed for introduction of the side chain of dl-shikonin.