Copper microwave-assisted

Fig. 10 2-Pyridone carboxylic acids 64 can be selectively decarboxylated to the saturated derivatives 65 via a reagent-free microwave-assisted method. Decarboxylation was also conducted under conventional heating but then copper cyanide was required resulting in mixtures of saturated and unsaturated 2-pyridones...

A microwave-assisted three-component reaction has been used to prepare a series of 1,4-disubstituted-1,2,3-triazoles with complete control of regiose-lectivity by click chemistry , a fast and efficient approach to novel functionalized compounds using near perfect reactions [76]. In this user-friendly procedure for the copper(l) catalyzed 1,3-dipolar cycloaddition of azides and alkynes, irradiation of an alkyl halide, sodium azide, an alkyne and the Cu(l) catalyst, produced by the comproportionation of Cu(0) and Cu(ll), at 125 °C for 10-15 min, or at 75 °C for certain substrates, generated the organic azide in situ and gave the 1,4-disubstituted regioisomer 43 in 81-93% yield, with no contamination by the 1,5-regioisomer (Scheme 18). 

Abstract A literature overview, up to the end of 2004, of the most important microwave-assisted transition-metal-mediated processes used for the decoration and construction of heterocycles is presented. The emphasis of the chapter lies in the use of palladium-assisted reactions but examples of copper- and nickel-mediated processes are also incorporated. 

Keywords Copper MAOS (Microwave assisted organic synthesis) Nickel Palladium Transition-metal-mediated bond formation... 

In 2003, Van der Fycken pubhshed a copper- and palladiirm-free microwave-assisted Sonogashira-type protocol in water with phenylacetylene as the alkyne (Scheme 51) [69]. The phase-transfer agent TBAB was used to facilitate... 

A potentially interesting development is the microwave-assisted transition-metal-free Sonogashira-type coupling reaction (Eq. 4.10). The reactions were performed in water without the use of copper(I) or a transition metal-phosphine complex. A variety of different aryl and hetero-aryl halides were reactive in water.25a The amount of palladium or copper present in the reaction system was determined to be less than 1 ppm by AAS-MS technique. However, in view of the recent reassessment of a similarly claimed transition-metal-free Suzuki-type coupling reaction, the possibility of a sub-ppm level of palladium contaminants found in commercially available sodium carbonate needs to be ruled out by a more sensitive analytical method.25 ... 

An improved strategy using microwave-assisted synthesis, involving a gallic acid core and copper-catalyzed [3+2] cycloaddition (CuAAc), afforded a series of glyco-dendrons.329 The straightforward synthesis of this series of glycodendrons was... 

The use of metals or metallic compounds in microwave-assisted reactions can also lead to damage to the reaction vessels. As metals interact intensively with microwaves, the formation of extreme hot spots may occur, which might weaken the vessel surface due to the onset of melting processes. This will destroy the stability of the vessels and may cause explosive demolition of the reaction containers. If catalysts are used which can produce elemental metal precipitates (for example, of palladium or copper), stirring is recommended to avoid the deposition of thin metal layers on the inner surfaces of the reaction vessels. 

Jung and Maderna have reported the microwave-assisted allylation of acetals with allyltrimethylsilane in the presence of copper(I) bromide as promoter (Scheme 6.77b) [162]. Stoichiometric amounts of copper(I) bromide are required and the reaction works best with aromatic acetals free from strongly electron-withdrawing substituents on the aromatic ring. 

For certain substrates, Fokin, Van der Eycken, and coworkers subsequently discovered that the azidation and ligation steps can be carried out in a one-pot fashion, thereby simplifying the overall protocol (Scheme 6.222) [397]. This procedure eliminates the need to handle organic azides, as they are generated in situ. Other applications of microwave-assisted copper(I)-catalyzed azide-alkyne ligations ( click chemistry ) have been reported [398],... 

Fast, solid state, microwave-assisted, synthesis. A short history of reactions carried out in the solid state under the influence of microwaves was reported by Kniep (1993) who presented this technique as characteristic of a fast solid-state chemistry and described the preparation of CuInS2 by using a method first developed by Whittaker and Mingos (1992) and extended by Landry and Barron(1993). Copper, indium and sulphur (all powders between 100 and 300 mesh) in a molar ratio 1 1 2 were thoroughly mixed and loaded into a silica ampoule. This, sealed under vacuum, was placed in a domestic microwave oven and irradiated at 400 W and 2450 MHz. 

Menendez et al. reported the synthesis of murrayafoline A (7) by palladium(II)-mediated oxidative double C-H activation of a diarylamine assisted by microwave irradiation (585). The aniline derivative 598 was obtained by O-methylation of 5-methyl-2-nitrophenol (625) followed by catalytic hydrogenation. The required diarylamine 654 was obtained by N-arylation of the aniline derivative 598 with phenyllead triacetate (653) in the presence of copper(II) acetate. Under microwave-assisted conditions, in the presence of more than the stoichiometric amount of palladium(II) acetate and a trace of dimethylformamide, the diarylamine 654 was cyclodehydrogenated to murrayafoline A (7) (585) (Scheme 5.47). 

Wang, J.X., Liu, Z.X., Hu, Y.L., Wei, B.G. and Kang, L.Q., Microwave-assisted copper catalysed coupling reaction of aryl halides with terminal alkynes, Synth. Commun., 2002, 32, 1937-1945. 

Synthesis of the benzopyran ring has also been performed by microwave-assisted copper-catalysed cross coupling of an aryl iodide with terminal alkynes, in the presence of copper(I) iodide/triphenylphosphine (Scheme 3.35)56. An alternative approach involving microwave heating of mixtures of salicylaldehyde and various derivatives of ethyl acetate in the presence of piperidine has enabled rapid Knoevenagel synthesis of coumarin derivatives (Scheme 3.35)57. 

The copper-catalysed hydrosilylation of vinylpyridines was significantly improved by microwave irradiation (Scheme 4.8). With 2-vinylpyridine, the reaction times were decreased by a factor of 360, and the yield of the product was enhanced from 5% under thermal conditions to 75% in the microwave-assisted reaction. Due to the much cleaner reaction under microwave conditions, the work-up procedure was considerably simplified30. 

Scheme 7.17 Microwave assisted copper(II) mediated coupling of jp-tolylboronic acid to various polymer bound heterocycles. 

Addition of alkynes to imines generated in situ can lead to quinolines when the reaction is conducted in the presence of copper chloride [126] or montmorillonite clay doped with copper bromide [127]. In the latter case, the reaction was performed under solvent-free conditions and was microwave assisted (Scheme 8.57). 

Vaisainen, A. and R. Suontomo. 2002. Comparison of ultrasound-assisted extraction, microwave-assisted acid leaching and reflux for the determination of arsenic, cadmium and copper in contaminated soil samples by electrothermal atomic absorption spectrometry. J. Anal. At. Spectrom. 17 739-742. 

A microwave-assisted one-pot two-step approach towards 1-arylindazoles relied on a copper-catalyzed intramolecular N-arylation-cyclization of in situ formed arylhydrazones [72], Traditionally, the Cul-diamine-complex catalyzed N-arylation reactions occurred at elevated temperatures (up to 110 °C) and required prolonged time (up to 24 h) to go to completion [73]. The com-... 

The palladium-catalyzed, microwave-assisted conversion of 3-bromopyridine to 3-cyanopyridine using zinc cyanide in dimethylformamide (DMF) has been reported <2000JOC7984>. Substoichiometric quantities of copper or zinc species improve both conversion rate and efficiency of Pd-catalyzed cyanation reactions <1998JOC8224>. A modification of this procedure uses a heterogeneous catalyst prepared from a polymer-supported triphenylphosphine resin and Pd(OAc)2 the nitriles were obtained from halopyridines in high yields <2004TL8895>. The successful cyanation of 3-chloropyridine is observed with potassium cyanide in the presence of palladium catalysts and tetramethylethylenediamine (TMEDA) as a co-catalyst <2001TL6707>. 

C. Lima, F. Barbosa, J. Krug, Comparison of ultrasound-assisted extraction, slurry sampling and microwave-assisted digestion for cadmium, copper and lead, J. Anal. Atom Spectrom., 15 (2000), 995-1000. 

The synthesis of symmetrically and unsymmetrically substituted J ,J -diarylimidazolin-2-ones by copper-catalyzed arylamidation under microwave-assisted and conventional conditions was studied <07S1403>. Palladium-catalyzed direct functionalization of imidazolinone with aryl halides has been reported <07JA7768>. 

Zadmard, R., Aghapoor, K., Bolourtchian, M., and Saidi, M.R. 1998. Solid composite copper-copper chloride assisted alkylation of naphthols promoted by microwave irradiation. Synthetic Communications, 28 4495-96. 

Trace and ultratrace impurities (Ti, Zn, Ga, Nb, Sn, Sb, Te, several lanthanides, Ta, Ir, Pt, Pb, Bi and U) in the xgg range and below in wet digested steel samples (with aqua regia in a microwave oven) have been determined by ICP-ToFMS. For Ca determination in steel, an analytical procedure was introduced with microwave assisted digestion and matrix separation by flow injection ICP-MS to solve the interference problem ( C 02 and Si °0 on analyte ion " " Ca+) after treatment with H2SO4 and HF, and a detection limit of 0.6(xgg was obtained. The determination of trace and ultratrace impurities in high purity (4N) copper samples, after digestion... 

Shore G, Yoo W-J, Li C-J et al (2009) Propargyl amine synthesis catalysed by gold and copper thin films by using microwave-assisted continuous-flow organic synthesis (MACOS). ChemEur J 16 126-133... 

Khajeh, M. Optimization of microwave-assisted extraction procedure for zinc and copper determination in food samples by Box-Behnken design. J. Food Compos. Anal. 22, 343-346 (2009)... 

---