Chao Qian

RANEY nickel-catalyzed reductive N-methylation of amines with paraformaldehyde: Theoretical and experimental study

RANEY® Ni-catalyzed reductive N-methylation of amines with paraformaldehyde has been investigated. This reaction proceeds in high yield with water as a byproduct. RANEY® Ni can be easily recovered and reused with a slight decrease of the yield. Using density functional theory (DFT), the mechanism of RANEY® Ni-catalyzed reductive N-methylation is discussed in detail. The reaction pathway involves the addition of amine with formaldehyde, dehydration to form the imine and hydrogenation. In the transition state of hemiaminal dehydration, the C–O bond cleavage of the aromatic amine is more difficult than that of the aliphatic amine. For the aromatic amine, a higher energy barrier must be overcome, which results in a relatively low yield. After addition of amine with formaldehyde and dehydration, imine is obtained and preferred to adsorb on the bridge site of the Ni(111) surface. The preferential pathways of imine hydrogenation involve the pre-adsorbed hydrogen atom attacking the nitrogen atom of the imine. The energy barrier of hydrogenation is much lower than that of addition and dehydration. Thus, the hydrogenation of imine is a relatively rapid reaction step. In the reductive N-methylation of secondary amine, the possible dehydration pathway is different from the one of the primary amine. In the dehydration of the secondary amine, the intermediate hemiaminal is initially adsorbed on the bridge site of the Ni(111) surface, then undergoes C–O bond cleavage, and eventually the hydroxyl is located in the bridge site. With the final hydrogenation, the product is obtained by adsorption on the top site of the Ni(111) surface.

Lewis basic ionic liquid as an efficient and facile catalyst for acetylation of alcohols, phenols, and amines under solvent-free conditions

The Lewis basic ionic liquid 1,8-diazabicyclo[5.4.0]undec-7-en-8-ium acetate was employed for the acetylation of various phenols, alcohols, and amines in good-to-excellent yields at 50xa0°C under solvent-free conditions in a short time. Compared with existing methods based on conventional catalysts and toxic solvents, the reported method is simple, mild and environmentally viable. Furthermore, the ionic liquid was conveniently separated from the products and easily recycled to catalyze other acetylation reactions with excellent yields.Graphical abstract.

Asymmetric reduction of imines with trichlorosilane catalyzed by valine-derived formamide immobilized onto magnetic nano-Fe3O4

Magnetic nano-Fe3O4-supported organocatalysts were synthesized by anchoring valine-derived formamide onto the surface of Fe3O4 magnetic nanoparticles, which were applied in the asymmetric reduction of imines with trichlorosilane at room temperature in toluene. The high level of yield and enantioselectivity catalyzed by magnetic nano-Fe3O4-supported organocatalysts was obtained. In the immobilization process, CuI-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) “click chemistry” was used as the anchored bridge. The magnetic nanoparticles can simplify the recovery of the organocatalyst and its separation from the reaction system. By an external magnet, the catalyst can be recycled and reused five times without a remarkable activity decline.

Combined experimental/theoretical study of D-glucosamine promoted Ullmann-type C–N coupling catalyzed by copper(I): does amino really count?

Ullmann type C–N coupling reaction catalyzed by copper(I) with D-glucosamine derivatives as promoters was studied by means of combined experimental/theoretical investigation. The catalytic role of D-glucosamine was addressed. In contrast with previous speculations, the amino group may not count in the catalytic cycle in which the oxidative addition/reductive elimination mechanism works. Experimental results are in good agreement with theoretical findings. Extensive work indicates the wide applicability of the C–N coupling strategy exploited in this work.

Combined experimental/theoretical study on D-glucosamine promoted regioselective sulfenylation of indoles catalyzed by copper

A combined experimental/theoretical investigation on the D-glucosamine promoted sulfenylation of indoles at the C3 position with sodium sulfinates catalyzed by copper is presented. The C3-sulfenylation of indoles shows good functional-group tolerance and yields. The 3-I-indole was identified as a crucial intermediate in the catalytic cycle. The catalytic role of [Cu(DMSO)2]2+ was addressed using quantum chemical calculations. In the interaction of [Cu(DMSO)2]2+ with indole, the [Cu(DMSO)2]2+ complex abstracts a hydrogen from the C3 of indole. The electronic origin for selective C–H bond activation of indole was revealed.

Efficient Ullmann C–N coupling catalyzed by a recoverable oligose-supported copper complex

The natural compound β-cyclodextrin supported copper complex (CuI@β-CD) was prepared and employed as catalyst for an Ullmann-type C–N coupling reaction of N-nucleophiles and aryl halides under mild conditions. Reactions with different substrates were examined, and moderate to excellent yields were obtained. In addition to the high efficiency, the reaction system is also noticeable due to the excellent recoverability and reusability of the catalyst.

N-alkylation of ethylenediamine with alcohols catalyzed by CuO-NiO/γ-Al2O3

A simple method for N-alkylation of 1,2-diaminoethane with different alcohols in a fixed-bed reactor using cheap CuO-NiO/γ-Al2O3 as the catalyst has been developed. The present catalytic system was applicable in the N-alkylation of 1,2-diaminoethane with both primary and secondary alcohols. Mono-N-alkylation of 1,2-diaminoethane with low-carbon alcohols resulted in high yields; the yields of tetra-N-alkylation of 1,2-diaminoethane with low-carbon alcohols declined markedly with the increase of the molecular volume of alcohols.

N-Methylation of amines with methanol in a hydrogen free system on a combined Al2O3–mordenite catalyst

N-Methyl amines play a major role in the production of medicines, pesticides, surfactants and dyes. N-Methylation of primary or second amines with methanol is considered to be a green path for the synthesis of N-methyl amines and the catalyst is key. In this article, the combined Al2O3–mordenite catalyst (mass fraction of alumina is 40%) with good activity, selectivity, lifetime and stability was prepared for N-methylation of various amines with methanol in a hydrogen free system in a fixed bed reactor, and characterized by XRD, N2 adsorption and NH3-TPD. Furthermore, the methanol adsorption was investigated by in situ FTIR, and the result indicated that methoxyl species may be the active species for the N-methylation of amines.

N-Hydroxyphthalimide catalyzed allylic oxidation of steroids with t-butyl hydroperoxide

A new and optimized procedure for the allylic oxidation of Δ(5)-steroids with t-butyl hydroperoxide in the presence of catalytic amounts of N-hydroxyphthalimide (NHPI) under mild conditions was developed, showing excellent regioselectivity and chemoselectivity (functional group compatibility). It was found that Co(OAc)2 could enhance the catalytic ability of NHPI resulting in better yields and shorter reaction times. The reaction mechanism and the scope of the reaction with a variety of Δ(5)-steroidal substrates were also investigated.

Improved synthesis of 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone and its derivatives

Improved synthesis of 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone has been developed. The dropwise addition of secondary amines was shown to reduce the dosages of amines drastically. In optimized conditions, the dosages of the catalysts were only 0.3–0.5xa0M of 2,6-di-tert-butylphenol. Removing the water generated in the step of Mannich base formation was found to hugely accelerate the whole reaction and improve the product yield. The catalytic activity of several annular secondary amines including morpholine and piperidine in this reaction has been researched. Most of the amines led to good yields. Using this method, 2,6-di-tert-butylphenol reacted with a wide range of aromatic aldehydes to produce nine diverse 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone derivatives of up to 75xa0% yield.Graphical Abstract