4630-82-4Relevant articles and documents
Kinetic aspects of the effect of CO pressure and methanol concentration on cyclohexene hydrocarbomethoxylation in the presence of the Pd(PPh 3)2Cl2-PPh3-p-toluenesulfonic acid catalytic system
Aver'Yanov,Sevost'Yanova,Batashev,Demerlii
, p. 39 - 45 (2013)
The dependence of the rate of the cyclohexene hydrocarbomethoxylation reaction catalyzed by the Pd(PPh3)2Cl2-PPh 3-p-toluenesulfonic acid system on the CO pressure and methanol concentration at temperatures varied in the range of 358-388 K has been investigated. The data are interpreted in terms of the previously proposed mechanism involving as intermediates ion pairs containing cationic hydride, alkyl, and acyl palladium complexes. By the least squares technique, apparent constants relating to the effect of CO pressure and methanol concentration have been estimated for the rate equation derived earlier. The apparent activation energies have been determined for these constants, and the following stability series of palladium complexes has been proposed on their basis: Pd(PPh 3)2 (CO)2 > Pd(PPh3)4 > Pd(PPh3)2 (CH3OH)2 > H Sol⊕ [Pd(PPh3)2 (Cl)(Sol)].
Supported palladium metal as heterogeneous catalyst precursor for the methoxycarbonylation of cyclohexene
Vavasori, Andrea,Bravo, Sara,Pasinato, Francesco,Kudaibergenov, Nurbolat,Pietrobon, Luca,Ronchin, Lucio
, (2020)
The methoxycarbonylation of cyclohexene has been carried out by using Pd metal deposited on a support as heterogeneous precursors instead of the homogeneous Pd(II) complexes usually proposed in literature. The two catalytic systems (homogeneous and heterogeneous) have been compared in methanol in the presence of free triphenylphosphine and p-toluenesulfonic acid as promoter. The precursor Pd on Amberlyst IRC 50 led to the best catalytic activity which is comparable to the activity obtained by using the homogeneous Pd(II)-catalyst. The leaching of the metal was negligible and the system has been efficiently recycled at least for three times. A reaction mechanism has been also proposed and discussed.
The concentration effects of reactants and components in the Pd(OAc) 2/p-toluenesulphonic acid/trans-2,3-bis(diphenylphosphinomethyl)- norbornane catalytic system on the rate of cyclohexene hydrocarbomethoxylation
Nifant'Ev,Sevostyanova,Averyanov,Batashev,Vorobiev,Toloraya,Bagrov,Tavtorkin
, p. 145 - 152 (2012)
The reactants and components of a catalytic system were studied for their effects on the rate of Pd-catalysed cyclohexene hydrocarbomethoxylation. First-order reaction rate dependences were established for cyclohexene and Pd(OAc)2, while non-monotonic rate dependences were determined for the diphosphine and p-toluenesulphonic acid concentrations and the SO pressure. The reaction was shown to follow first-order kinetics when the methanol concentration was below 0.4 mol/L; however, the reaction rate slowed upon a further increase in the methanol concentration. The obtained results were interpreted by considering a hydride mechanism supplemented with ligand exchange reactions, which decreased the activity of the catalyst, and with hydride complex annihilations by p-toluenesulphonic acid, resulting in complete loss of catalytic activity. Treatment of the proposed mechanism using the quasi-equilibrium concentration method gave a kinetic equation for the reaction that was consistent with the experimental data.
Effect of temperature and CO pressure on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2 - PPh3 - TsOH system
Sevostyanova,Averyanov,Batashev,Rodionova,Vorob'ev
, p. 837 - 842 (2014)
The quantitative regularities of the effect of CO pressure and temperature on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2 - PPh3 - TsOH system were defined. Extremal dependences of the reaction rate on the CO pressure were revealed in the temperature range from 353 to 383 K. To interpret the obtained results, the catalytic cycle was constructed which included the hydride, alkyl, and acyl palladium complexes of the cationic type as intermediates. It was proposed that the catalyst is partially converted into an inactive form due to the exchange between ligands. The experiments on the effect of the CO pressure on the reaction rate made it possible to estimate the apparent rate constants for the kinetic reaction equation obtained earlier.
Regioselective 6-endo cyclization of 5-carbomethoxy-5-hexenyl radicals: A convenient synthesis of derivatives of the 1-azabicyclo[2.2.1]heptyl system
Della, Ernest W.,Kostakis, Chris,Smith, Paul A.
, p. 363 - 365 (1999)
(equation presented) Ring closure of the 5-carbomethoxy-5-hexenyl radical is governed largely by the polar effect, and as predicted by frontier molecular orbital considerations, endo cyclization predominates, leading to cyclohexyl rather than cyclopentyl-based products. In cyclization of the corresponding β-ammonio species 18, stereoelectronic effects do not distinquish between attack of the radical center at C3 or C4, each of which represents a 5-exo ring closure. The radical 18 is found to cyclize with great rapidity and with high stereoselectivity to give bicyclo[2.2.1]heptane products in accordance with expectation based on polar effects; this transformation represents an excellent entry to the physiologically important bicyclic ester 17.
Direct Hydrodecarboxylation of Aliphatic Carboxylic Acids: Metal- and Light-Free
Burns, David J.,Lee, Ai-Lan,McLean, Euan B.,Mooney, David T.
supporting information, p. 686 - 691 (2022/01/28)
A mild and inexpensive method for direct hydrodecarboxylation of aliphatic carboxylic acids has been developed. The reaction does not require metals, light, or catalysts, rendering the protocol operationally simple, easy to scale, and more sustainable. Crucially, no additional H atom source is required in most cases, while a broad substrate scope and functional group tolerance are observed.
N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading
Berkessel, Albrecht,Biswas, Animesh,Harnying, Wacharee,Sudkaow, Panyapon
supporting information, p. 19631 - 19636 (2021/08/09)
We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02–1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
Electrochemical esterification via oxidative coupling of aldehydes and alcohols
Smeyne, Dylan,Verboom, Katherine,Bryan, Maria,LoBue, James,Shaikh, Abid
supporting information, (2021/03/26)
An electrolytic method for the direct oxidative coupling of aldehydes with alcohols to produce esters is described. Our method involves anodic oxidation in presence of TBAF as supporting electrolyte in an undivided electrochemical cell equipped with graphite electrodes. This method successfully couples a wide range of alcohols to benzaldehydes with yields ranging from 70 to 90%. The protocol is easy to perform at a constant voltage conditions and offers a sustainable alternative over conventional methods.
Scalable On-Demand Production of Purified Diazomethane Suitable for Sensitive Catalytic Reactions
Sheeran, Jillian W.,Campbell, Kiersten,Breen, Christopher P.,Hummel, Gerald,Huang, Changfeng,Datta, Anamika,Boyer, Serge H.,Hecker, Scott J.,Bio, Matthew M.,Fang, Yuan-Qing,Ford, David D.,Russell, M. Grace
supporting information, p. 522 - 528 (2021/02/03)
We have developed a convenient development-scale reactor (0.44 mol/h) to prepare diazomethane from N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in ～80% yield. Diazomethane (CH2N2) made with this reactor is extracted into nitrogen gas from the liquid reaction mixture, effectively removing it from reagents and byproducts that may interfere in subsequent reactions. Vertically oriented tubular reactors were used to produce and consume diazomethane in situ. Key features of this reactor include high productivity and correspondingly low reactor volume (reactor volume/liquid flow rate = 6.5 min) and a commercially available gas/liquid separator equipped with a selectively permeating hydrophilic membrane. The design of the reactor keeps the inventory below 53 mg of CH2N2 during normal operation. The reactor was demonstrated by generating CH2N2 that was used in a connected continuous reactor. We evaluated esterification reactions and a continuous Pd-catalyzed cyclopropanation reaction with the reactor and achieved high conversion with 1.5 and 4.1 equiv of MNTS precursor, respectively.
Iodoarene-Catalyzed Oxyamination of Unactivated Alkenes to Synthesize 5-Imino-2-Tetrahydrofuranyl Methanamine Derivatives
Deng, Xiao-Jun,Liu, Hui-Xia,Zhang, Lu-Wen,Zhang, Guan-Yu,Yu, Zhi-Xiang,He, Wei
, p. 235 - 253 (2021/01/09)
Reported here is the room-temperature metal-free iodoarene-catalyzed oxyamination of unactivated alkenes. In this process, the alkenes are difunctionalized by the oxygen atom of the amide group and the nitrogen in an exogenous HNTs2 molecule. This mild and open-air reaction provided an efficient synthesis to N-bistosyl-substituted 5-imino-2-tetrahydrofuranyl methanamine derivatives, which are important motifs in drug development and biological studies. Mechanistic study based on experiments and density functional theory calculations showed that this transformation proceeds via activation of the substrate alkene by an in situ generated cationic iodonium(III) intermediate, which is subsequently attacked by an oxygen atom (instead of nitrogen) of amides to form a five-membered ring intermediate. Finally, this intermediate undergoes an SN2 reaction by NTs2 as the nucleophile to give the oxygen and nitrogen difunctionalized 5-imino-2-tetrahydrofuranyl methanamine product. An asymmetric variant of the present alkene oxyamination using chiral iodoarenes as catalysts also gave promising results for some of the substrates.
