Magnetically separable g‐C3N4 hybrid nanocomposite: Highly efficient and eco‐friendly recyclable catalyst for one‐pot synthesis of α‐aminonitriles

A magnetically separable graphitic carbon nitride nanocomposite (Fe₃O₄/g‐C₃N₄) as a catalyst for the three‐component condensation reactions of carbonyl compounds, amines and trimethylsilylcyanide was thoroughly investigated. The reaction of these three components was found to be efficient, economical and green and took place in the presence of a catalytic amount of the magnetically separable catalyst to yield the corresponding α‐aminonitriles in good to excellent yields. The prepared nanocomposite was characterized using scanning electron microscopy and energy‐dispersive X‐ray and Fourier transform infrared spectroscopies. The nanocomposite was also found to be reusable could be recovered easily and reused several times without distinct deterioration in its catalytic activity.     

Synthesis of α‐Aminonitriles and 5‐Substituted 1H‐Tetrazoles Using an Efficient Nanocatalyst of Fe3O4@SiO2–APTES‐supported Trifluoroacetic Acid

Fe₃O₄@SiO₂–APTES‐supported trifluoroacetic acid nanocatalyst was used for the one‐pot synthesis of α‐aminonitriles via a three‐component reaction of aldehydes (or ketones), amines, and sodium cyanide. This method produced a high yield of 75–96% using only a small amount of the catalyst (0.05 g) in EtOH at room temperature. The catalyst was also employed for the synthesis of 5‐substituted 1H‐tetrazoles from nitriles and sodium azide in EtOH at 80°C. The tetrazoles were produced with good‐to‐excellent yields in a short reaction time of 4 h. Both synthetic methods were carried out in the absence of an organic volatile solvent. Because the supported trifluoroacetic acid generated a solid acid on the surface, thus the acid corrosiveness was not a serious challenge. This heterogeneous nanocatalyst was magnetically recovered and reused several times without significant loss of catalytic activity.     

Mechanochemical Strecker Reaction: Access to α‐Aminonitriles and Tetrahydroisoquinolines under Ball‐Milling Conditions

A mechanochemical version of the Strecker reaction for the synthesis of α‐aminonitriles was developed. The milling of aldehydes, amines, and potassium cyanide in the presence of SiO₂ gave the corresponding α‐aminonitriles in good to high yields. The high efficiency of the mechanochemical Strecker‐type multicomponent reaction allowed the one‐pot synthesis of tetrahydroisoquinolines after a subsequent internal N‐alkylation reaction.     

Gallic acid grafted to amine‐functionalized magnetic nanoparticles as a proficient catalyst for environmentally friendly synthesis of α‐aminonitriles

An effective approach of one‐pot catalytic Strecker reaction between aromatic aldehydes, aniline or toluidine and trimethylsilyl cyanide in the presence of amine‐functionalized Fe₃O₄@SiO₂ nanoparticles grafted with gallic acid (GA) as a powerful catalyst was developed. The fabricated reusable catalyst demonstrated high efficiency in the synthesis of α‐aminonitriles along with facile work‐up procedure. Fe₃O₄@SiO₂‐NH₂‐GA was characterized by Fourier transform‐infrared spectroscopy, scanning electron microscopy image, vibrating‐sample magnetometer curve, energy‐dispersive X‐ray analysis and thermogravimetric analysis.     

Niobium(V) chloride‐catalyzed synthesis of α‐aminonitriles with simultaneous reaction of aldehydes,amines and trimethylsilyl cyanide

A simple and efficient one‐pot method has been developed for the synthesis of α‐aminonitriles by concurrent reaction of aldehydes, amines and trimethylsilyl cyanide with a catalytic amount of NbCl₅ (10 mol%) in CH₃CN at room temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

Design,synthesis, characterization and catalytic performance of a new cellulose‐based magnetic nanocomposite in the one‐pot three‐component synthesis of α‐aminonitriles

A sulfonated magnetic cellulose‐based nanocomposite was prepared and characterized using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction and Fourier transform infrared spectroscopy. Then, it was used as a green nanocatalyst for the synthesis of α‐aminonitriles by a one‐pot three‐component condensation reaction of aldehydes or ketones, amines and trimethylsilylcyanide in ethanol at room temperature. The reaction procedure is simple, yields are very high, reaction time is very short and the catalyst can be easily separated from the reaction mixture and reused in subsequent reactions without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Fe(OTf)3‐Catalyzed α‐Benzylation of Aryl Methyl Ketones with Electrophilic Secondary and Aryl Alcohols

Acid‐catalyzed Friedel–Crafts alkylation of 1,3‐dicarbonyl compounds with electrophilic alcohols, is known to be an effective C? C bond forming reaction. However, until now, this reaction has not been amenable for α‐alkylation of aryl methyl ketones because of the notoriously low nucleophilicities of these compounds. Therefore, α‐alkylation of aryl methyl ketone relies on precious metal catalysts and also, the use of primary alcohols is mandatory. In this study, we found that a system composed of a Fe(OTf)₃ catalyst and chlorobenzene solvent is sufficient to promote the title Friedel–Crafts reaction by using benzhydrols as electrophiles. 3,4‐Dihydro‐9‐(2‐hydroxy‐4,4‐dimethyl‐6‐oxo‐1‐cyclohexen‐1‐yl)‐3,3‐dimethyl‐xanthen‐1(2 H)‐one was also applicable as an electrophile in this type of benzylation reaction. On the basis of this result, a three‐component reaction of salicylaldehyde, dimedone, and aryl methyl ketone was also developed, and this provided an efficient way for the synthesis of densely substituted 4H‐chromene derivatives.     

Solving the loss of orthogonality during the polyaddition of α‐azide‐ω‐alkyne monomers catalyzed by Cu(PPh3)3Br: Application to the synthesis of high‐molar mass polytriazoles

Polyaddition of an α‐azide‐ω‐alkyne monomer by Cu(PPh₃)₃Br catalyzed 1,3‐dipolar cycloaddition was thoroughly studied as a model system to investigate the orthogonality of this click chemistry process. Indeed, loss of chain‐end functionality and occurrence of side reactions have a tremendous impact on the molar mass of polymers obtained by step growth polymerization. Particularly, SEC, ¹H, and ³¹P NMR experiments have highlighted the occurrence of a Staudinger side‐reaction between azide chain‐ends and PPh₃ from the copper(I) catalyst that dramatically alters M_n of the resulting polytriazoles. A significant enhancement of M_n could be achieved by using an alternative catalyst and optimized experimental conditions, that is, dilution and reaction time. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2470–2476, 2010     

Novel nano molten salt tetra‐2,3‐pyridiniumporphyrazinato‐oxo‐vanadium tricyanomethanide as a vanadium surface‐free phthalocyanine catalyst: Application to Strecker synthesis of α‐aminonitrile derivatives

Efficient and recyclable novel nano tetra‐2,3‐pyridiniumporphyrazinato‐oxo‐vanadium tricyanomethanide, {[VO(TPPA)][C(CN)₃]₄}, as a vanadium surface‐free phthalocyanine‐based molten salt catalyst was successfully designed, produced and used for the Strecker synthesis of α‐aminonitrile derivatives through a one‐pot three‐component reaction between aromatic aldehydes, trimethylsilyl cyanide and aniline derivatives under neat conditions at 50 °C. This catalyst was well characterized using Fourier transform infrared, UV–visible, X‐ray photoelectron and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, scanning and high‐resolution transmission electron microscopies, inductively coupled plasma mass spectrometry and thermogravimetric analysis. The catalyst can be simply recovered and reused several times without significant loss of catalytic activity.     

Synthesis of 4‐((2‐hydroxynaphthalen‐1‐yl)(aryl)methyl)‐5‐methyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐ones using nano‐Zn‐[2‐boromophenyl‐salicylaldimine‐methylpyranopyrazole]Cl2 nanoparticles

Nano‐Zn‐[2‐boromophenyl‐salicylaldimine‐methylpyranopyrazole]Cl₂ (nano‐[Zn‐2BSMP]Cl₂) as a nanoparticle Schiff base complex and a catalyst was introduced for the solvent‐free synthesis of 4‐((2‐hydroxynaphthalen‐1‐yl)(aryl)methyl)‐5‐methyl‐2‐phenyl‐1H‐pyrazol‐3(2H)‐ones by the multicomponent condensation reaction of various aromatic aldehydes, β‐naphthol, ethyl acetoacetate, and phenyl hydrazine at room temperature.     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.     

Ethylene/α‐olefin copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Copolymerizations of ethylene with α‐olefins (i.e., 1‐hexene, 1‐octene, allylbenzene, and 4‐phenyl‐1‐butene) using the bis(β‐enaminoketonato) titanium complexes [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ ( 1a : R₁ = CF₃, R₂ = CH₃; 1b : R₁ = Ph, R₂ = CF₃; and 1c : R₁ = t‐Bu, R₂ = CF₃), activated with modified methylaluminoxane as a cocatalyst, have been investigated. The catalyst activity, comonomer incorporation, and molecular weight, and molecular weight distribution of the polymers produced can be controlled over a wide range by the variation of the catalyst structure, α‐olefin, and reaction parameters such as the comonomer feed concentration. The substituents R₁ and R₂ of the ligands affect considerably both the catalyst activity and comonomer incorporation. Precatalyst 1a exhibits high catalytic activity and produces high‐molecular‐weight copolymers with high α‐olefin insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6323–6330, 2005     

Synthesis α‐aminonitrile through anodic cyanation of N‐benzylpiperidine

Six‐membered cyclic α‐aminonitrile has been prepared from anodic cyanation of N‐benzylpiperidine. Good yields of α‐aminonitriles could be obtained through potentiostatic electrolysis under different conditions. The results also explain why high yield α‐aminonitriles could not be obtained under constant current electrolysis.     

Catalytic Enantioselective Reaction of α‐Aminoacetonitriles Using Chiral Bis(imidazoline) Palladium Catalysts

The catalytic enantioselective reaction of diphenylmethylidene‐protected α‐aminoacetonitriles with imines has been developed. Good yields and diastereo‐ and enantioselectivities were observed for the reaction of various imines using chiral bis(imidazoline)/Pd catalysts. The reaction of α‐aminonitriles with di‐tert‐butyl azodicarboxylate afforded chiral α,α‐diaminonitriles in high yields with high enantioselectivities.     

An Alternative to the Classical α‐Arylation: The Transfer of an Intact 2‐Iodoaryl from ArI(O2CCF3)2

The α‐arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ³‐iodanes. Here, we describe an alternative metal‐free α‐arylation using ArI(O₂CCF₃)₂ as the source of a 2‐iodoaryl group. The reaction is applicable to activated ketones, such as α‐cyanoketones, and works with substituted aryliodanes. This formal C? H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α‐(2‐iodoaryl)ketones are versatile synthetic building blocks.     

(C6F5)3B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

The development of an efficient method for the site‐selective substitution of unprotected phenols has long been considered as an attractive but challenging task. Herein, we describe a highly chemo‐ and ortho‐selective substitution reaction of phenols with α‐aryl α‐diazoacetates with commercially available (C₆F₅)₃B as the catalyst. This reaction proceeds under simple and mild conditions with high efficiency, it features a wide substrate scope and can be easily scaled up.     

Photoinduced and thermal reactions of α‐cyano‐β‐bromomethylcinnamide with 1‐benzyl‐1,4‐dihydronicotinamide

The photoinduced reaction of a mixture of (Z)‐α‐cyano‐β‐bromomethylcinnamide (1) and (E)‐α‐cyano‐β‐bromomethylcinnamide (2) with 1‐benzyl‐1, 4‐dihydronicotinamide produces a mixture of the (E)‐ and (Z)‐ isomers of α‐cyano‐β‐methylcinnamide (3 and 4). Using spin‐trapping technique for monitoring reactive intermediate, it is shown that the reaction proceeds via electron transfer‐debromination‐H abstraction mechanism. The thermal reaction of the same substrate with BNAH at 60°C in the dark gives three products: the (E)‐ and (Z)‐isomers of α‐cyano‐β‐methylcinnamide and a dehydrodimeric product; 2, 7‐dicyano‐3, 6‐diphenylocta‐2, 4, 6‐trien‐1, 8‐dioic amide (7). Based on product analysis, scavenger experiment and cyclic voltammetry, an electron transfer‐debromination‐disproportionation mechanism is proposed.     

B(C6F5)3/Chiral Phosphoric Acid Catalyzed Ketimine–Ene Reaction of 2‐Aryl‐3H‐indol‐3‐ones and α‐Methylstyrenes

The enantioselective ketimine–ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine–ene reactions of 2‐aryl‐3H‐indol‐3‐ones with α‐methylstyrenes were achieved by utilizing a B(C₆F₅)₃/chiral phosphoric acid (CPA) catalyst. These ketimine–ene reactions proceed well with low catalyst loading (B(C₆F₅)₃/CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2‐allyl‐indolin‐3‐ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C₆F₅)₃ significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen‐bonding interactions, especially the enhanced N?H???O hydrogen‐bonding interaction, differentiates the free energy of the transition states of CPA and B(C₆F₅)₃/CPA, thereby inducing the improvement of stereoselectivity.     

Highly Stereoselective β‐Mannopyranosylation via the 1‐α‐Glycosyloxy‐isochromenylium‐4‐gold(I) Intermediates

While the gold(I)‐catalyzed glycosylation reaction with 4,6‐O‐benzylidene tethered mannosyl ortho‐alkynylbenzoates as donors falls squarely into the category of the Crich‐type β‐selective mannosylation when Ph₃PAuOTf is used as the catalyst, in that the mannosyl α‐triflates are invoked, replacement of the ^?OTf in the gold(I) complex with less nucleophilic counter anions (i.e., ^?NTf₂, ^?SbF₆, ^?BF₄, and ^?BAr₄^F) leads to complete loss of β‐selectivity with the mannosyl ortho‐alkynylbenzoate β‐donors. Nevertheless, with the α‐donors, the mannosylation reactions under the catalysis of Ph₃PAuBAr₄^F (BAr₄^F=tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate) are especially highly β‐selective and accommodate a broad scope of substrates; these include glycosylation with mannosyl donors installed with a bulky TBS group at O3, donors bearing 4,6‐di‐O‐benzoyl groups, and acceptors known as sterically unmatched or hindered. For the ortho‐alkynylbenzoate β‐donors, an anomerization and glycosylation sequence can also ensure the highly β‐selective mannosylation. The 1‐α‐mannosyloxy‐isochromenylium‐4‐gold(I) complex ( Cα ), readily generated upon activation of the α‐mannosyl ortho‐alkynylbenzoate ( 1 α ) with Ph₃PAuBAr₄^F at ?35 °C, was well characterized by NMR spectroscopy; the occurrence of this species accounts for the high β‐selectivity in the present mannosylation.     

Self‐assembled three‐dimensional flower‐like α‐Fe2O3 nanostructures and their application in catalysis

Three‐dimensional flower‐like α‐Fe₂O₃ nanostructures have been successfully synthesized by a simple surfactant‐free environmental friendly solvolthermal process. The as‐prepared products were investigated by X‐ray powder diffraction, transmission electron microscopy, and field emission scanning electron microscopy. By adjusting the synthetic parameters, the shape of the α‐Fe₂O₃ nanostructures can be controlled. The three‐dimensional flower‐like α‐Fe₂O₃ nanostructures were found to be highly active as catalysts for phenol alkylation. The effects of various parameters, such as reaction temperature, reaction time and the amount of catalyst, were studied. The catalyst was stable and could be reused three times in normal atmosphere without suffering appreciable loss in catalytic activity. Copyright © 2009 John Wiley & Sons, Ltd.