Ruthenium catalysed N-alkylation of amines with alcohols

The conversion of primary amines into secondary amines has been achieved using alcohols as the alkylating agent, catalysed by [Ru(p-cymene)Cl2]2 and a bidentate phosphine ligand.     

Palladium catalyzed N-alkylation of amines with alcohols

An iron oxide immobilized palladium catalyst was prepared for the N-alkylation of amines with alcohols under base and organic ligand free conditions. Applying the optimized reaction conditions, the coupling reactions of amines and alcohols with various structures could be realized with up to 99% isolated yields. The catalysts were studied by XRD, BET, and XPS and the mechanism was studied by DFT calculations.     

Selective N-alkylation of amines using nitriles under hydrogenation conditions: facile synthesis of secondary and tertiary amines

Nitriles were found to be highly effective alkylating reagents for the selective N-alkylation of amines under catalytic hydrogenation conditions. For the aromatic primary amines, the corresponding secondary amines were selectively obtained under Pd/C-catalyzed hydrogenation conditions. Although the use of electron poor aromatic amines or bulky nitriles showed a lower reactivity toward the reductive alkylation, the addition of NH(4)OAc enhanced the reactivity to give secondary aromatic amines in good to excellent yields. Under the same reaction conditions, aromatic nitro compounds instead of the aromatic primary amines could be directly transformed into secondary amines via a domino reaction involving the one-pot hydrogenation of the nitro group and the reductive alkylation of the amines. While aliphatic amines were effectively converted to the corresponding tertiary amines under Pd/C-catalyzed conditions, Rh/C was a highly effective catalyst for the N-monoalkylation of aliphatic primary amines without over-alkylation to the tertiary amines. Furthermore, the combination of the Rh/C-catalyzed N-monoalkylation of the aliphatic primary amines and additional Pd/C-catalyzed alkylation of the resulting secondary aliphatic amines could selectively prepare aliphatic tertiary amines possessing three different alkyl groups. According to the mechanistic studies, it seems reasonable to conclude that nitriles were reduced to aldimines before the nucleophilic attack of the amine during the first step of the reaction.     

N-alkylation of aromatic amines with tris(trifluoroethyl)phosphate

Results of a study of the use of tris(trifluoroethyl)phosphate for the alkylation of aromatic amines are reported. Tris(trifluoroethyl)phosphate is a satisfactory reagent for introducing a trifluoroethyl group into aromatic amines, except for those containing N-alkyl, hydroxyl, or alkoxyl substituents and for those containing strongly electron-withdrawing groups such as nitro and carboxyl.     

Mild nonepimerizing N-alkylation of amines by alcohols without transition metals

A one-pot two-step sequence involving an oxidation/imine-iminium formation/reduction allowed the N-alkylation of amines by alcohols without any epimerization when optically active alcohols and amines are involved in the process.     

Kinetic studies of the N-alkylation of secondary amines with 1,2-dichloroethane

The reactions of 1,2-dichloroethane with 2-(ethylamino)ethanol or diethylamine have been investigated in several solvents from 51 to 80°C. A reaction mechanism has been proposed where 1,2-dichloroethane reacts with the secondary amines in both bimolecular substitution (SN 2) and elimination (E2) reactions; the substitution product is rapidly converted in an aziridinium ion and undergoes a consecutive reaction with the starting amine to give a tetrasubstituted ethylenediamine. The rate constants as well as the activation energies of these reactions have been determined. © 1994 John Wiley & Sons, Inc.     

Solvent engineering: an effective tool to direct chemoselectivity in a lipase-catalyzed Michael addition

A solvent engineering strategy was implemented in order to control the chemoselectivity in a lipase-catalyzed Michael addition reaction. This strategy was revealed as a high-effective tool for the selective synthesis of Michael adduct 3 or aminolysis product 4 from benzylamine 1 and methyl crotonate 2. Chemoselectivity of the enzymatic process was elucidated in terms of polarity of the medium, hence, adduct 3 was preferentially accumulated in hydrophobic medium, whereas in polar solvents the amide 4 was preferentially formed.     

Reductive N-alkylation of aromatic amines and nitro compounds with nitriles using polymethylhydrosiloxane

The potential utility of polymethylhydrosiloxane (PMHS) as a reducing agent for reductive N-alkylation of aromatic amines and nitro compounds using nitriles as an alkylating agent and Pd(OH)₂/C as a catalyst is described. The application of this method for the synthesis of several heterocyclic compounds is also reported.     

Manganese dioxide catalyzed N-alkylation of sulfonamides and amines with alcohols under air

By simply running the reactions under air and solvent-free conditions using catalytic amounts of manganese dioxide, a practical and efficient N-alkylation method for a variety of sulfonamides and amines using alcohols as green alkylating reagents was developed.     

CpIr-catalyzed N-alkylation of amines with alcohols. A versatile and atom economical method for the synthesis of amines

A versatile and highly atom economical catalytic system consisting of [Cp^∗IrCl₂]₂/NaHCO₃ (Cp^∗=pentamethylcyclopentadienyl) for the N-alkylation of amines with primary and secondary alcohols as alkylating reagents has been developed. For example, the reaction of equimolar amounts of aniline and benzyl alcohol in the presence of [Cp^∗IrCl₂]₂ (1.0 mol % Ir) and NaHCO₃ (1.0 mol %) in toluene at 110 °C gives N-benzylaniline in 94% yield. The present catalytic system is applicable to the N-alkylation of both primary and secondary amines, and only harmless water is produced as co-product. A wide variety of secondary and tertiary amines can be synthesized with high atom economy under mild and less-toxic conditions. One-pot sequential N-alkylation leading to tertiary amines bearing three different substituents is also described.     

Direct N-alkylation of amines with alcohols using AlCl_3 as a Lewis acid

A substitution reaction of amines with alcohols for N-alkylated amines has been developed using inexpensive AlCl_3 without any ligand or additive.Either aromatic or aliphatic amines and primary or secondary alcohols perform the AlCl_3-mediated reaction smoothly to afford various N-alkylated amines in satisfactory yields.     

Reusable Co-nanoparticles for general and selective N-alkylation of amines and ammonia with alcohols

A general cobalt-catalyzed N-alkylation of amines with alcohols by borrowing hydrogen methodology to prepare different kinds of amines is reported. The optimal catalyst for this transformation is prepared by pyrolysis of a specific templated material, which is generated in situ by mixing cobalt salts, nitrogen ligands and colloidal silica, and subsequent removal of silica. Applying this novel Co-nanoparticle-based material, >100 primary, secondary, and tertiary amines including N-methylamines and selected drug molecules were conveniently prepared starting from inexpensive and easily accessible alcohols and amines or ammonia.

A general cobalt-catalyzed N-alkylation of amines with alcohols by borrowing hydrogen methodology to prepare different kinds of amines is reported.     

Copper-catalyzed N-alkylation of amides and amines with alcohols employing the aerobic relay race methodology

By employing aerobic oxidation to aldehydes as a more effective alcohol activation strategy, we developed a green Cu-catalyzed N-alkylation method for various amides and amines with alcohols. This reaction is more advantageous than the literature methods for it uses a ligand-free copper catalyst, can be readily carried out under milder aerobic conditions and generates water as the only byproduct. More importantly, based on our mechanistic studies and also supported by the literature, rather than following the previously-proposed mechanisms, we deduce that the newly-proposed relay race process should be the most possible and a more rational mechanism for the reactions, especially under aerobic conditions.     

Pd/ZnO在乙炔选择加氢反应中的不同催化机制研究(英文)

化学选择性是评价催化剂性能最重要的参数之一,它直接决定了产物的经济价值及后续的分离成本.传统的负载型金属催化剂由于其金属粒径分布不均,且不同原子数组成的粒子通常具有特征产物选择性,从而限制化学选择性的提高;另一方面,对于金属多原子活性中心,反应物在催化剂表面可以存在多种吸附构型进而衍化为不同产物,产物可控性差.因此,获得金属尺寸均一,且具有原子分散的活性中心,即单原子催化剂,成为官能团多相催化转化高选择性的迫切需求.本课题组通过400 oC还原1%-Pd/ZnO得到PdZn金属间化合物,依据其规律排布的Pd-Zn-Pd单元获得Pd基单原子催化剂.该催化剂在乙烯化工中少量乙炔的加氢转化反应中获得令人欣喜的催化性能——兼具有乙炔的高转化率和乙烯的高选择性.结合微量吸附量热、理论计算等表征,Pd活性中心在PdZn金属间化合物中的特殊空间排布是其优异催化性能的根源,即乙炔以较强的σ键吸附在两个相邻的单Pd金属中心,易吸附活化加氢生成乙烯,而乙烯则吸附于单Pd金属中心,较弱的π键形式吸附有利于其脱附避免过渡加氢.基于前期研究,构筑具有均一单金属中心的负载型单原子催化剂是获得高选择性的另一有效方法,且较之于PdZn金属间化合物催化剂,该类单原子催化剂兼具有原子利用率最大化的优点.本文采用等体积浸渍法制备Pd/ZnO催化剂,通过降低Pd金属含量(1 wt%→0.1 wt%→0.01 wt%)并在较低的温度下(100 oC)还原(H2-TPR表明高温还原形成PdZn金属间化合物型合金)得到负载型单原子催化剂(Pd1/ZnO SAC).高分辨电镜结果表明,当Pd负载量由1%降至0.1%,金属纳米颗粒的粒径尺寸显著降低,而在0.01%-Pd/ZnO催化剂表面,Pd活性中心则以单原子状态分散于载体ZnO表面.X-射线吸收光谱及电子能谱表明,随着负载量的降低,Pd活性物种具有更高的正电性.该催化剂在乙炔选择性加氢反应中表现出更加优越的催化性能,具有与PdZn催化剂相当的高选择性,而更优的比活性.这归结于Pd1/ZnO单原子催化剂的Pdδ+单原子活性中心有助于其与乙炔的静电相互作用并吸附活化加氢生成乙烯,并促使乙烯以较弱的π键吸附,从而易于从催化剂表面脱附获得高选择性.     

Synthesis of methyl carbamates from primary aliphatic amines and dimethyl carbonate in supercritical CO2: effects of pressure and cosolvents and chemoselectivity

[reaction: see text] At 130 degrees C, in the presence of CO2 (5-200 bar), primary aliphatic amines react with dimethyl carbonate (MeOCO2Me, DMC) to yield methyl carbamates (RNHCO2Me) and N-methylation side-products (RNHMe and RNMe2). The pressure of CO2 largely influences both the reaction conversion and the selectivity toward urethanes: in general, conversion goes through a maximum (70-80%) in the midrange (40 bar) and drops at lower and higher pressures, whereas selectivity is continuously improved (from 50% up to 90%) by an increase of the pressure. This is explained by the multiple role of CO2 in (i) the acid/base equilibrium with aliphatic amines, (ii) the reactivity/solubility of RNHCO2- nucleophiles with/in DMC, and (iii) the inhibition of competitive N-methylation reaction of the substrates. Cosolvents also affect the reaction: in particular, a drop in selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2- moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)n NH2, X = NH2, OH; n = 1, 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding methyl carbamates [XC6H4(CH2)n NHCO2Me] in 39-65% isolated yields.     

Synthesis and reactivity of a 9-membered azaenediyne: importance of proximity effect in N-alkylation

Synthesis of a 9-membered azaenediyne has been achieved for the first time via intramolecular N-alkylation; the importance of proximity of the reacting centres via cobalt carbonyl complexation of the acetylenic moiety and not the activation of propargylic carbon has been demonstrated.