High-intensity ultrasound and microwave, alone or combined, promote Pd/C-catalyzed aryl–aryl couplings

Cravotto, Giancarlo; Beggiato, Marina; Penoni, Andrea; Palmisano, Giovanni; Tollari, Stefano; Lévêque, Jean–Marc; Bonrath, Werner

doi:10.1016/j.tetlet.2005.02.015

Cited by 137 publications

(56 citation statements)

References 19 publications

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“…[32] Few promising results have been obtained in glycerol. [5] Several papers have reported on the palladium-catalyzed Suzuki couplings carried out under MW and US irradiation, [33] even in a combined fashion, [34] with several advantages. Glycerol dissolved organic substrates, inorganic bases, and palladium complexes as a polar organic solvent, and allowed for the reaction product to be easily isolated through a simple extraction process using glycerol-immiscible solvents, such as diethyl ether, and also permitted catalyst recycling.…”

Section: Resultsmentioning

confidence: 99%

Efficient Synthetic Protocols in Glycerol under Heterogeneous Catalysis

et al. 2011

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The massive increase in glycerol production from the transesterification of vegetable oils has stimulated a large effort to find novel uses for this compound. Hence, the use of glycerol as a solvent for organic synthesis has drawn particular interest. Drawbacks of this green and renewable solvent are a low solubility of highly hydrophobic molecules and a high viscosity, which often requires the use of a fluidifying co-solvent. These limitations can be easily overcome by performing reactions under high-intensity ultrasound and microwaves in a standalone or combined manner. These non-conventional techniques facilitate and widen the use of glycerol as a solvent in organic synthesis. Glycerol allows excellent acoustic cavitation even at high temperatures (70-100 °C), which is otherwise negligible in water.Herein, we describe three different types of applications: 1) the catalytic transfer hydrogenation of benzaldehyde to benzyl alcohol in which glycerol plays the dual role of the solvent and hydrogen donor ; 2) the palladium-catalyzed Suzuki cross-coupling; and (3) the Barbier reaction. In all cases glycerol proved to be a greener, less expensive, and safer alter-native to the classic volatile organic solvents.

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Section: Resultsmentioning

confidence: 99%

Efficient Synthetic Protocols in Glycerol under Heterogeneous Catalysis

et al. 2011

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“…[30] We developed two types of combined MW/US reactors. [32] The first uses two reaction cells (one for each kind of irradiation) joined by short lengths of tubing to allow the reacting liquid to circulate between them, while the second uses a single reaction cell for simultaneous irradiation with both energy sources.…”

Section: Resultsmentioning

confidence: 99%

“…[28] Ligand-free Pd-catalyzed homo-and cross-couplings of boronic acids with aryl halides have been successfully performed by our group in aqueous media under high-intensity US and MW, either alone or in a combined fashion. [29,30] We carried out combined irradiation in a flow reactor, obtaining the expected biaryls in higher yields and shorter time than using sonication or microwaves separately. [30] Proceeding from our previous experience on the catalysis of Suzuki [29,30] and Heck reactions [31] we present here our recent results on reactions carried out with a very low ligandless catalyst load under MW or simultaneous US/MW irradiation.…”

Section: Introductionmentioning

confidence: 99%

Heck Reactions with Very Low Ligandless Catalyst Loads Accelerated by Microwaves or Simultaneous Microwaves/Ultrasound Irradiation

Palmisano

Bonrath²,

Boffa

et al. 2007

Adv Synth Catal

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Heck couplings were carried out ligandless in air with very low catalyst loads under microwave or simultaneous microwave/ultrasound irradiation.in the range of 0.01-0.1 mol % or palladium-oncarbon (Pd/C) 10 % in the range of 1.0-2.0 mol %, most aryl iodides and bromides gave high yields under conventional heating (120 8C) in 18 h. Microwave irradiation alone or, better still, combined with high-intensity ultrasound, strongly promotes the reaction, generally decreasing reaction times to 1 h. Electron-poor aryl chlorides such as 4-chloroacetophenone and 1-chloro-4-nitrobenzene reacted with styrene to afford high product yields in the presence of 0.25 mol % PdA C H T U N G T R E N N U N G (OAc) 2 or 2.0-3.0 mol % Pd/C. In several cases the addition of a co-catalyst, either rhodium tris(triphenylphosphine) chloride, 0.005 mol %, or a copper(I) salt (iodide or bromide), 2.0-4.0 mol %, proved very advantageous. 4-Bromo-and 4-chloroacetophenone afforded up to 15 % of oxidation products, namely the corresponding 4-halobenzoic acid and 4-styrylbenzoic acid, a drawback that was avoided by working under a nitrogen atmosphere.

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“…In a trial series of 15 different iodo-and bromoaryls and 7 boronic acids, the use of both energy sources drastically reduced reaction times. The homo-and cross-couplings were also carried out in a new reactor featuring combined US and MW irradiation with further improvement of this potentially sustainable synthetic method (Table 1) [29].…”

Section: Suzuki-miyaura Couplingmentioning

confidence: 99%

Pd/C Catalysis under Microwave Dielectric Heating

2017

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Microwave-assisted organic synthesis (MAOS) provides a novel and efficient means of achieving heat organic reactions. Nevertheless, the potential arcing phenomena via microwave (MW) interaction with solid metal catalysts has limited its use by organic chemists. As arcing phenomena are now better understood, new applications of Pd/C-catalyzed reactions under MW dielectric heating are now possible. In this review, the state of the art, benefits, and challenges of coupling MW heating with heterogeneous Pd/C catalysis are discussed to inform organic chemists about their use with one of the most popular heterogeneous catalysts.

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High-intensity ultrasound and microwave, alone or combined, promote Pd/C-catalyzed aryl–aryl couplings

Cited by 137 publications

References 19 publications

Efficient Synthetic Protocols in Glycerol under Heterogeneous Catalysis

Efficient Synthetic Protocols in Glycerol under Heterogeneous Catalysis

Heck Reactions with Very Low Ligandless Catalyst Loads Accelerated by Microwaves or Simultaneous Microwaves/Ultrasound Irradiation

Pd/C Catalysis under Microwave Dielectric Heating

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