One-pot two-step microwave-assisted reaction in constructing 4,5-disubstituted pyrazolopyrimidines

[reaction: see text] A microwave-assisted reaction was developed to facilitate the construction of 4,5-disubstituted pyrazolopyrimidines. This one-pot two-step process involves a sequential S(N)Ar displacement of the C4 chloro substituent with various anilines and amines, followed by a Suzuki coupling reaction with different boronic acids. Using microwave irradiation leads to high product conversion, low side product formation, and shorter reactions.     

Exploration of structure and mechanism of insoluble gels formed in microwave-assisted Suzuki coupling for poly(9,9-dihexylfluorene)s

A series of poly(9,9-dihexylfluorene)s (PDHFs) have been synthesized via microwave-assisted Suzuki and Yamamoto coupling reactions. Compared with the conventional oil-bath heating (48 h, Mw 20100 g/mol by Suzuki reaction and Mw 24000 g/mol by Yamamoto reaction), microwave-assisted polymerization can yield PDHFs with higher molecular weights (Mw 37200 g/mol by Suzuki reaction and Mw 43400 g/mol by Yamamoto reaction) in shorter time (14 and 60 min). However, sometimes formation of insoluble gels was observed together with PDHF in Suzuki coupling reaction. PDHF and insoluble gels were analyzed by XPS, elemental analysis, FTIR, TGA and DSC. Experimental results demonstrated that H2O might take part in the Suzuki coupling reaction under microwave condition, which could make the cross-linking reaction occur and form gels.     

Pd-N-heterocyclic carbene (NHC) organic silica: synthesis and application in carbon-carbon coupling reactions

The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica was prepared using sol-gel method and its application in Heck and Suzuki reactions was demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, with excellent yield, without any change in catalytic activity for at least five reaction cycles, with negligible Pd concentration in the end product.     

Microwave-assisted C-C coupling reaction using polymer-supported electron-rich oxime palladacycles in aqueous condition

Previously reported polymer-supported oxime palladacycle catalyst has shown effective catalytic activity in the Suzuki coupling reaction. In this work, the effect of microwave on reaction rate and induction period was examined by comparing them with the conventional heating. Undoubtedly, microwave heating effectively enhanced the catalytic performance in the Suzuki reaction. In-depth observation of the kinetic profiles revealed that the microwave irradiation not only reduced the overall reaction time but also significantly decreased the induction period to less than 3 min. Finally, the performance of the catalyst in water, coupling of potassium phenyltrifluoroborate and aryl bromides, and recyclability were also examined.     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Rapid Microwave-promoted Base-free Suzuki Coupling Reaction of Sodium Tetraphenylborate with Hypervalent Iodonium Salts in Water

The palladium chloride-catalyzed Suzuki coupling reaction of sodium tetraphenylborate with hypervalent iodonium salts was achieved under microwave irradiation in water without base in excellent yield. A convenient and rapid method for formation of carbon-carbon bonds was afforded.     

Suzuki coupling reactions of 2,4,6-trialkoxyphenylboronic acids with enol triflates: asymmetric synthesis of a lactone template for calyxin assemblage

Suzuki coupling reactions between 2,4,6-trialkoxyphenylboronic acids and enol triflates have been found to occur in excellent yield, while the use of an enol tosylate failed to give any of the desired product. This coupling reaction has led to the synthesis of a lactone which could serve as a precursor to several calyxin analogues.     

Supramolecular reactor in an aqueous environment: aromatic cross Suzuki coupling reaction at room temperature

[reaction: see text] We have investigated supramolecular reactors for the Suzuki coupling reactions of aryl halides with phenyl boronic acids by using self-assembly of amphiphilic rod-coil molecules in aqueous solution at room temperature. All the rod-coil molecules synthesized in this work showed to self-assemble into discrete micelles consisting of aromatic rod bundles encapsulated by hydrophilic poly(ethylene oxide) coils. We present a comparative study of rod-coil molecules' efficiency as supramolecular reactors for Suzuki coupling reaction. The closed-packed aromatic bundles play an efficient role in supramolecular reactors for the coupling reactions at room temperature. The supramolecular reactor based on hexa-p-phenylene confers unprecedented activity, allowing reactions to be performed at very low catalyst levels, without conventional heating or microwave.     

Microwave-assisted aqueous Suzuki coupling reactions catalyzed by ionic palladium(II) complexes

Suzuki coupling is one of the most powerful methods for the synthesis of biaryls. We have prepared and characterized a series of unsymmetrical sulfonated water-soluble Pd(II)-pyridyl imine complexes and investigated them as catalysts for the Suzuki cross-coupling reaction in water under microwave irradiation. The compounds proved to be effective catalysts.     

Solution-phase microwave-assisted synthesis of unsubstituted and modified alpha-quinque- and sexithiophenes

The facile synthesis of poorly soluble unsubstituted and modified alpha-quinque- and sexithiophenes under microwave irradiation in the liquid phase is described. The use of microwave irradiation allowed these compounds to be prepared in a few minutes and at high yields by means of the Suzuki cross-coupling reaction. Unsubstituted sexithiophene was obtained in 10 min via the one-pot borylation/Suzuki reaction, purified according to a very simple procedure, and isolated in 84% yield. The efficient synthesis of two new methylated quinque- and sexithiophenes displaying liquid crystalline properties is reported. A new microwave-assisted methodology for the conversion of aldehyde-terminated quinque- and sexithiophenes into the corresponding cyano derivatives is also described. The use of microwaves was extended to the Sonogashira coupling reaction and found to be very effective in the preparation of a quinquethiophene containing acetylenic spacers. The electronic and optical characterization of this compound is reported and discussed in relation to that of unsubstituted quinquethiophene.     

Efficient Suzuki-Miyaura coupling of (hetero)aryl chlorides with thiophene- and furanboronic acids in aqueous n-butanol

An efficient Suzuki cross-coupling protocol enables the reaction of N-hetero and normal aryl chlorides with thiophene- and furanboronic acids. Coupling is effected in aqueous n-butanol as the solvent in near quantitative yield with a catalyst loading of 0.1-1 mol %. For heterocyclic substrates aqueous catalysis is found to be more efficient than Suzuki coupling under anhydrous conditions. The developed Suzuki coupling procedure utilizes biodegradable solvents and is useful for large scale reactions, as it includes the facile product separation from a biphasic solvent mixture without the need for additional organic solvents during workup.     

Polymer-assisted solution-phase (PASP) Suzuki couplings employing an anthracene-tagged palladium catalyst

A general method for polymer-assisted solution-phase (PASP) Suzuki reactions employing a combination of anthracene-tagged palladium catalyst and anthracene-tagged boronic acid with a polymer-supported carbonate base is reported. The anthracene-tagged catalyst allows for the easy removal of the Pd catalyst along with the dissociated phosphine ligand and phosphine oxide byproducts by sequestration through a chemoselective Diels-Alder reaction with a maleimide resin. The polymer-supported carbonate base facilitates the removal of excess boronic acid and the borane-containing byproducts present at the end of the coupling reaction. The Suzuki coupling reaction can be efficiently conducted by using combinations of the anthracene-tagged Pd catalyst, polymer-supported carbonate base, and anthracene-tagged boronic acid to yield the desired product in high purity and yield without the use of chromatography.     

Aryl-guanidine/Pd-catalyzed Suzuki Cross-coupling Reaction at Room Temperature

Four aryl-guanidines(AG)were synthesized and used for the palladium-catalyzed Suzuki cross-coupling reaction to test the catalytic activity.In the presence of steric bulk AG,when aryl bromide and arylb...     

Suzuki coupling of aryl chlorides with phenylboronic acid in water, using microwave heating with simultaneous cooling

[reaction: see text]. We present here a methodology for the Suzuki coupling of aryl chlorides with phenylboronic acid using Pd/C as a catalyst, water as a solvent, and microwave heating. We show that simultaneous cooling in conjunction with microwave heating prolongs the lifetime of the aryl chloride substrates during the course of the reaction and, as a result, yields of the desired biaryl as well as overall recovery of material can be increased.     

Methane coupling in microwave plasma under atmospheric pressure

Methane coupling in microwave plasma under atmospheric pressure has been investigated.The effects of molar ratio n(CH4)/n(H2),flow rate and microwave power on the reaction have been studied.(1)With the decrease of n(CH4)/n(H2)ratio,methane conversion,C2 hydrocarbon yield,energy yield and space-time yield of acetylene increased,but the yield of carbon deposit decreased.(2)With the increase of microwave power,energy yield of acetylene decreased,but space-time yield of acetylene increased.(3)With the increase of flow rate,energy yield and space-time yield of acetylene increased first and then decreased.Finally,under the reaction conditions of CH4 flow rate of 700 mL/min,n(CH4)/n(H2)ratio of 1/4 and microwave power of 400 W,the energy yield and space-time yield of acetylene could reach 0.337 mmol/kJ and 12.3 mol/(s m3),respectively.The reaction mechanism of methane coupling in microwave plasma has been investigated based on the thermodynamics of chemical reaction.Interestingly,the acetylene yield of methane coupling in microwave plasma was much higher than the maximum thermodynamic yield of acetylene.This phenomenon was tentatively explained from non-expansion work in the microwave plasma system.     

5-甲基-2，3-二苯基-1，5-苯并硫氮杂卓-4(5H)-酮的合成

以2-甲硫基苯胺为原料,通过酰化、碘环化以及Suzuki交叉偶联反应,合成了5-甲基-2,3-二苯基-1,5-苯并硫氮杂卓-4(5H)-酮。 分别考察了催化剂对酰化反应、溶剂对碘环化反应的影响,以及催化剂、配体、碱和温度等因素对Suzuki交叉偶联反应的影响,在最佳的反应条件下,反应总收率为68.5%,中间产物和目标产物的结构经IR、NMR和MS等测试技术得以确证。     

Direct synthesis of 5-aryltriazole acyclonucleosides via Suzuki coupling in aqueous solution

5-Aryltriazole acyclonucleosides with various aromatic groups on the triazole ring were synthesized via the Suzuki coupling reaction in aqueous solution and promoted by microwave irradiation. Careful optimization of the reaction conditions led in good to excellent yields to the Suzuki products, while the cyclization side-reaction could be completely suppressed.     

9-fluorenylphosphines for the Pd-catalyzed sonogashira, suzuki, and Buchwald-Hartwig coupling reactions in organic solvents and water

The lithiation/alkylation of fluorene leads to various 9-alkyl-fluorenes (alkyl=Me, Et, iPr, -Pr, -C18H25) in>95% yields, for which lithiation and reaction with R2PCl (R=Cy, iPr, tBu) generates 9-alkyl, 9-PR2-fluorenes which constitute electron-rich and bulky phosphine ligands. The in-situ-formed palladium-phosphine complexes ([Na2PdCl4], phosphonium salt, base, substrates) were tested in the Sonogashira, Suzuki, and Buchwald-Hartwig reactions of aryl chlorides and aryl bromides in organic solvents. The Sonogashira coupling of aryl chlorides at 100-120 degrees C leads to>90% yields with 1 mol% of Pd catalyst. The Suzuki coupling of aryl chlorides typically requires 0.05 mol% of Pd catalyst at 100 degrees C in dioxane for quantitative product formation. To carry out "green" cross-coupling reactions in water, 9-ethylfluorenyldicyclohexylphosphine was reacted in sulphuric acid to generate the respective 2-sulfonated phosphonium salt. The Suzuki coupling of activated aryl chlorides by using this water-soluble catalyst requires only 0.01 mol% of Pd catalyst, while a wide range of aryl chlorides can be quantitatively converted into the respective coupling products by using 0.1-0.5 mol% of catalyst in pure water at 100 degrees C. Difficult substrate combinations, such as naphthylboronic acid or 3-pyridylboronic acid and aryl chlorides are coupled at 100 degrees C by using 0.1-0.5 mol% of catalyst in pure water to obtain the respective N-heterocycles in quantitative yields. The copper-free aqueous Sonogashira coupling of aryl bromides generates the respective tolane derivatives in>95% yield.     

Mechanistic Aspects of Monomer, Polymer Formation, and Synthesis of PQ-Alt-Dialkyl-fluorene Conjugated Copolymer

Suzuki coupling reaction is widely used in the construction of conjugated polymers; however, there is still no report describing the mechanism and coupling of 9,10-phenanthrenequinone（PQ） building blocks via Suzuki reaction because PQ is sensitive to bases and light. Herein is reported the efficient Suzuki coupling of PQ with 9,10-dialkylfluorene with Na2CO3 as basic species and high molecular weight PQ-Alt-Dialkyl-Fluorene conjugated copolymer obtained in an yield of 42%. Based on the characterization data and well-accepted literature, we proposed a step-by-step mechanistic explanation for the formation of the PQ containing alternating conjugated copolymer.     

水相钯催化Suzuki反应

钯催化的Suzuki反应是构建Csp2—Csp2键的主要方法之一,已广泛应用于医药、天然产物及先进功能材料等联芳类化合物的合成.近年来,水相Suzuki反应引起了人们的高度关注.对以纯水及水/有机混溶剂为介质的水相Suzuki反应的研究进展作一综述,特别是围绕如何解决水相Suzuki反应活性的问题,以催化体系为主线,重点介绍了水溶性配体/钯、表面活性剂、微波促进的非水溶性配体/钯及无配体钯等催化体系在水相Suzuki反应中的应用.