An Efficient and Selective Nickel-Catalyzed Direct N-Alkylation of Anilines with Alcohols

NNO Pincer-Supported Pd(II)-Catalyzed Reductive N-Alkylation of Challenging Nitroarenes with Alcohols via Borrowing Hydrogen Strategy

A sustainable catalytic synthesis of selective monoalkylated amines from nitroarenes and alcohols by new palladium(II)-NNO pincer-type complexes has been described. Herein, a series of Pd(II) complexes [Pd(NNO)PPh3] (1-3) are synthesized and characterized by analytical and spectroscopic (IR, NMR, and HR-MS) methods. The solid-state molecular structures of two complexes are established by X-ray single-crystal diffraction. Furthermore, the catalytic N-alkylation of challenging nitroarenes with primary and secondary alcohols has been performed by the well-defined palladium(II) complexes via borrowing hydrogen strategy. The current protocol offers a wide range of monoalkylated amines (26 examples) with a maximum yield of 87% utilizing 1 mol % of catalyst loading. Gratifyingly, the catalytic system works well under mild reaction conditions and atom economy with water is the only byproduct. Furthermore, control experiments confirm the formation of probable intermediates (aniline, aldehyde, and imine), and deuterium labeling authenticates the borrowing hydrogen mechanism. A gram-scale synthesis of an alkylated product clearly demonstrates the synthetic efficacy of the present catalytic methodology.

Atomic-Level Asymmetric Tuning of the Co1-N3P1 Catalyst for Highly Efficient N-Alkylation of Amines with Alcohols

Despite the extensive development of non-noble metals for the N-alkylation of amines with alcohols, the exploitation of catalysts with high selectivity, activity, and stability still faces challenges. The controllable modification of single-atom sites through asymmetric coordination with a second heteroatom offers new opportunities for enhancing the intrinsic activity of transition metal single-atom catalysts. Here, we prepared the asymmetric N/P hybrid coordination of single-atom Co1-N3P1 by absorbing the Co-P complex on ZIF-8 using a concise impregnation-pyrolysis process. The catalyst exhibits ultrahigh activity and selectivity in the N-alkylation of aniline and benzyl alcohol, achieving a turnover number (TON) value of 3480 and a turnover frequency (TOF) value of 174-h. The TON value is 1 order of magnitude higher than the reported catalysts and even 37-fold higher than that of the homogeneous catalyst CoCl2(PPh3)2. Furthermore, the catalyst maintains its high activity and selectivity even after 6 cycles of usage. Controlling experiments and isotope labeling experiments confirm that in the asymmetric Co1-N3P1 system, the N-alkylation of aniline with benzyl alcohol proceeds via a transfer hydrogenation mechanism involving the monohydride route. Theoretical calculations prove that the superior activity of asymmetric Co1-N3P1 is attributed to the higher d-band energy level of Co sites, which leads to a more stable four-membered ring transition state and a lower reaction energy barrier compared to symmetrical Co1-N4.

Selective N-Alkylation of Aminobenzenesulfonamides with Alcohols for the Synthesis of Amino-(N-alkyl)benzenesulfonamides Catalyzed by a Metal-Ligand Bifunctional Ruthenium Catalyst

[(p-Cymene)Ru(2,2'-bpyO)(H2O)] was proven to be an efficient catalyst for the synthesis of amino-(N-alkyl)benzenesulfonamides via selective N-alkylation of aminobenzenesulfonamides with alcohols. It was confirmed that functional groups in the bpy ligand are crucial for the activity of catalysts. Furthermore, the utilization of this catalytic system for the preparation of a biologically active compound was presented.

Nickel-Catalyzed α-Alkylation of Arylacetonitriles with Challenging Secondary Alcohols

Nickel(II) complex 1 was utilized as a sustainable catalyst for α-alkylation of arylacetonitriles with challenging secondary alcohols. Arylacetonitriles with a wide range of functional groups were tolerated, and various cyclic and acyclic secondary alcohols were utilized to yield a large number of α-alkylated products. The plausible mechanism involves the base-promoted activation of precatalyst 1 to an active catalyst 2 (dehydrochlorinated product) which activates the O-H and C-H bonds of the secondary alcohol in a dehydrogenative pathway.

Harnessing alcohols as sustainable reagents for late-stage functionalisation: synthesis of drugs and bio-inspired compounds

Alcohol is ubiquitous with unparalleled structural diversity and thus has wide applications as a native functional group in organic synthesis. It is highly prevalent among biomolecules and offers promising opportunities for the development of chemical libraries. Over the last decade, alcohol has been extensively used as an environmentally friendly chemical for numerous organic transformations. In this review, we collectively discuss the utilisation of alcohol from 2015 to 2023 in various organic transformations and their application toward intermediates of drugs, drug derivatives and natural product-like molecules. Notable features discussed are as follows: (i) sustainable approaches for C-X alkylation (X = C, N, or O) including O-phosphorylation of alcohols, (ii) newer strategies using methanol as a methylating reagent, (iii) allylation of alkenes and alkynes including allylic trifluoromethylations, (iv) alkenylation of N-heterocycles, ketones, sulfones, and ylides towards the synthesis of drug-like molecules, (v) cyclisation and annulation to pharmaceutically active molecules, and (vi) coupling of alcohols with aryl halides or triflates, aryl cyanide and olefins to access drug-like molecules. We summarise the synthesis of over 100 drugs via several approaches, where alcohol was used as one of the potential coupling partners. Additionally, a library of molecules consisting over 60 fatty acids or steroid motifs is documented for late-stage functionalisation including the challenges and opportunities for harnessing alcohols as renewable resources.

Recent advances in cross-coupling of alcohols via borrowing hydrogen catalysis

Application of the borrowing hydrogen strategy facilitates utilization of abundantly available alcohols for linear or branched long-chain alcohols. Selective synthesis of such alcohols is highly challenging and involves the utilization of transition metal catalysts towards the desired cross-coupled product. Herein, we have highlighted recent advances (from 2015 to 2023) towards the synthesis of higher alcohols. Major focus has been given to the development of ligands, including transition metal catalysts. Judicious catalyst design plays a key role in the alkylation process and is summarised in this review.

Manganese Complex Catalyzed Sequential Multi-component Reaction: Enroute to a Quinoline-Derived Azafluorenes

The development of innovative synthetic strategies for constructing complex molecular structures is the heart of organic chemistry. This significance of novel reactions or reaction sequences would further enhance if they permitted the synthesis of new classes of structural motifs, which have not been previously created. The research on the synthesis of heterocyclic compounds is one of the most active topics in organic chemistry due to the widespread application of N-heterocycles in life and material science. The development of a new catalytic process that employs first-row transition metals to produce a range of heterocycles from renewable raw materials is considered highly sustainable approach. This would be more advantageous if done in an eco-friendly and atom-efficient manner. Herein we introduce, the synthesis of various new quinoline based azafluorenes via sequential dehydrogenative multicomponent reaction (MCR) followed by C(sp3)-H hydroxylation and annulation. Our newly developed, Mn-complexes have the ability to direct the reaction in order to achieve a high amount of desired functionalized heterocycles while minimizing the possibility of multiple side reactions. We also performed a series of control experiments, hydride trapping experiments, reaction kinetics, catalytic intermediate and DFT studies to comprehend the detailed reaction route and the catalyst's function in the MCR sequence.

Construction of Oxygen Vacancy-Rich TiO2 Nanocrystals for Boosting the Ammonolysis of Caprolactam to 6-Aminocapronitrile

Hexamethylene diamine, an important chemical intermediate for polyamides, can be synthesized through the two-step route of caprolactam (CPL) ammonolysis to 6-aminocapronitrile (ACN), followed by hydrogenation. This method has received increasing attention from academia and industry. However, studies on the catalyst structure-performance correlation in CPL ammonolysis are still sporadic. In this work, a series of anatase TiO2 with different oxygen vacancy concentrations was prepared by chemical reduction using NaBH4. The oxygen vacancy on TiO2 surface, presented as Ti3+ sites, substantially enhances the adsorption and activation of NH3, which are demonstrated as the key steps in ammonolysis. Owing to the synergistic effect of Ti3+ and Ti4+ species, the CPL conversion rate and ACN selectivity of 85 and 97%, respectively, are achieved within 250 h. Density functional theory calculations showed that the intermediates on oxygen vacancy-rich TiO2 had a more favorable adsorption energy compared to those on intact TiO2, which is in good agreement with the experimental results.

Recent advances in the selective semi-hydrogenation of alkyne to (E)-olefins

Considering the potential importance and upsurge in demand, the selective semi-hydrogenation of alkynes to (E)-olefins has attracted significant interest. This article highlights the recent advances in newer technologies and important methodologies directed to (E)-olefins from alkynes developed from 2015 to 2023. Notable features summarised include the catalyst or ligand design and control of product selectivity based on precious and nonprecious metal catalysts for semi-hydrogenation to (E)-olefins. Mechanistic studies for various catalytic transformations, including synthetic application to bioactive compounds, are summarised.

Titanium-Catalyzed Selective N-Alkylation of Amines with Alcohols via Borrowing Hydrogen Methodology

The N-alkylation of amines with alcohols using earth-abundant and nonprecious metal catalysts has gained considerable attention in the pharmaceutical industry. We described titanium-catalyzed synthetic protocol for N-alkylation of amines with alcohols via borrowing hydrogen or hydrogen autotransfer reactions. The methodology enables the selective monoalkylation of various substituted (hetero)aromatic amines in good to excellent yields (up to 97% yield). The importance of the protocol was further demonstrated by the applicability of earth-abundant metal catalysis and the synthesis of 32 N-alkylated amines. The work allows the utilization of titanium-based catalysts for various reactions to expand the nature blueprint in catalysis.

N-Alkylation of aromatic amines with alcohols by using a commercially available Ru complex under mild conditions

An N-alkylation procedure has been developed under very mild conditions using a known commercially available Ru-based catalyst. As a result, a wide range of aromatic primary amines has been selectively alkylated with several primary alcohols, yielding the corresponding secondary amines in high yields. The methodology also enables the methylation of anilines in refluxing methanol and the preparation of a set of heterocycles in a straightforward way.

Ce4+/Ce3+ Redox Effect-Promoted CdS/CeO2 Heterojunction Photocatalyst for the Atom Economic Synthesis of Imines under Visible Light

The employment of stoichiometric alcohols and amines for imine synthesis under mild and green reaction conditions is still a challenge in the field. In this work, based on our research foundation in the thermocatalytic synthesis of imines over ceria, a CdS/CeO2 heterojunction photocatalyst was constructed and successfully realized the atom-economic synthesis of imines under visible light without additives at room temperature. Mechanistic experiments and corresponding characterizations indicated that the CdS/CeO2 heterojunction can improve the separation efficiency of photogenerated carriers, which can be further enhanced by the Ce4+/Ce3+ redox pair by rapidly combining photogenerated e-. The in situ-reduced Ce3+ can better activate O2 to form Ce-O-O·, which, together with h+, efficiently accelerates alcohol oxidation, which is the rate-determined step for the synthesis of imines via oxidative coupling reaction of alcohol and amine. In addition, our photocatalyst exhibited fairly decent reusability and substrate universality. This work solves problems of using base additives and excess amine or alcohol in the reported photocatalytic systems and provides new insight for designing CeO2-based photocatalytic oxidation catalysts.

Nickel-Catalyzed Alkylation of Oxindoles with Secondary Alcohols

Herein, we have demonstrated a simple nickel-catalyzed C-3-selective alkylation of 2-oxindoles using a wide variety of secondary alkyl alcohols. As a special highlight, functionalization of the cholesterol derivative was reported. Control experiments, initial mechanistic studies, and deuterium-labeling experiments were performed for the alkylation process.

N-Alkylation of Amines by C1-C10 Aliphatic Alcohols Using A Well-Defined Ru(II)-Catalyst. A Metal-Ligand Cooperative Approach

A Ru(II)-catalyzed efficient and selective N-alkylation of amines by C1-C10 aliphatic alcohols is reported. The catalyst [Ru(L^1a)(PPh₃)Cl₂] (1a) bearing a tridentate redox-active azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L^1a) is air-stable, easy to prepare, and showed wide functional group tolerance requiring only 1.0 mol % (for N-methylation and N-ethylation) and 0.1 mol % of catalyst loading for N-alkylation with C3-C10 alcohols. A wide array of N-methylated, N-ethylated, and N-alkylated amines were prepared in moderate to good yields via direct coupling of amines and alcohols. 1a efficiently catalyzes the N-alkylation of diamines selectively. It is even suitable for synthesizing N-alkylated diamines using (aliphatic) diols producing the tumor-active drug molecule MSX-122 in moderate yield. 1a showed excellent chemo-selectivity during the N-alkylation using oleyl alcohol and monoterpenoid β-citronellol. Control experiments and mechanistic investigations revealed that the 1a-catalyzed N-alkylation reactions proceed via a borrowing hydrogen transfer pathway where the hydrogen removed from the alcohol during the dehydrogenation step is stored in the ligand backbone of 1a, which in the subsequent steps transferred to the in situ formed imine intermediate to produce the N-alkylated amines.

Synthesis of 1,4-Diazacycles by Hydrogen Borrowing

We report the syntheses of 1,4-diazacycles by diol-diamine coupling, uniquely made possible with a (pyridyl)phosphine-ligated ruthenium(II) catalyst (1). The reactions can exploit either two sequential N-alkylations or an intermediate tautomerization pathway to yield piperazines and diazepanes; diazepanes are generally inaccessible by catalytic routes. Our conditions tolerate different amines and alcohols that are relevant to key medicinal platforms. We show the syntheses of the drugs cyclizine and homochlorcyclizine in 91% and 67% yields, respectively.

N-Heterocyclic Carbene-Supported Nickel-Catalyzed Selective (Un)Symmetrical N-Alkylation of Aromatic Diamines with Alcohols

The "borrowing hydrogen" (BH) approach for the N-alkylation of phenylenediamines using alcohols as coupling partners is highly challenging due to the selectivity issue of the generated products. Furthermore, the development of base-metal systems that can potentially substitute precious metals with competitive activity is a major challenge in BH catalysis. We present herein an efficient protocol for the N,N'-di-alkylation of aromatic diamines using an in situ-generated Ni-NHC complex from NiCl₂ and the ligand L1, which gave access to a wide range of N,N'-di-alkylated orthophenylene diamines (rather than the generally observed benzimidazole derivatives), meta- and para-phenylene diamines along with 2,6-diamino pyridine derivatives in good to excellent yields. Moreover, the catalyst system was also successful in the derivatization of a clinically important drug molecule, Dapsone. Notably, the present protocol could be applied effectively to synthesize unsymmetrically substituted N,N'-di-alkylated diamines via sequential alkylation and is the first report in the base-metal system to the best of our knowledge. Diverse control experiments including the deuterium incorporation studies suggest that the present protocol proceeds via a BH sequence.

Zn(II)-Catalyzed Selective N-Alkylation of Amines with Alcohols Using Redox Noninnocent Azo-Aromatic Ligand as Electron and Hydrogen Reservoir

We report a sustainable and eco-friendly approach for selective N-alkylation of various amines by alcohols, catalyzed by a well-defined Zn(II)-catalyst, Zn(L^a)Cl₂ (1a), bearing a tridentate arylazo scaffold. A total of 57 N-alkylated amines were prepared in good to excellent yields, out of which 17 examples are new. The Zn(II)-catalyst shows wide functional group tolerance, is compatible with the synthesis of dialkylated amines via double N-alkylation of diamines, and produces the precursors in high yields for the marketed drugs tripelennamine and thonzonium bromide in gram-scale reactions. Control reactions and DFT studies indicate that electron transfer events occur at the azo-chromophore throughout the catalytic process, which shuttles between neutral azo, one-electron reduced azo-anion radical, and two-electron reduced hydrazo forms acting both as electron and hydrogen reservoir, enabling the Zn(II)-catalyst for N-alkylation reaction.

A binuclear Cu(II) complex as an efficient photocatalyst for N-alkylation of aromatic amines

Visible-light driven photoreactions using transition metal complexes as catalysts are currently a research hotspot in developing environmentally friendly sustainable processes. To develop a potential copper-based photocatalyst, a binuclear Cu(II) complex has been synthesized using a Mannich base ligand viz. 2,4-dichloro-6-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)phenol (H₂L). The photocatalyst has been characterized using ESI-MS and single crystal X-ray diffraction. Under the irradiation of visible light, the catalyst can catalyze hydrogen auto-transfer in N-alkylated amine formation and benzyl alcohol oxidation reactions with excellent conversion. A plausible mechanistic pathway for catalytic reactions has been explored through ESI-MS spectrometric, UV-Vis spectroscopic and computational studies.

Half-Sandwich Iridium Complexes with Hydrazone Ligands: Synthesis and Catalytic Activity in N-Alkylation of Anilines or Nitroarenes with Alcohols via Hydrogen Autotransfer

Here, we synthesize a series of hydrazone-based N,O-chelate half-sandwich iridium complexes through a facile route. All air-stable iridium complexes show high catalytic activity in N-alkylation of a broad scope of aniline derivatives and alcohols with liberating water as the sole byproduct. This reaction provides a smooth route to synthesize diverse monoalkylated amines in good to excellent yields at moderate temperature with a low catalyst loading. Moreover, the challenging N-alkylation process using nitroarene substrates as coupling partners is also carried out in this catalytic system. The mechanistic study shows that the present iridium catalysis process proceeds through a hydrogen borrowing mechanism. All iridium(III) complexes 1-4 are characterized by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis.

Highly Chemoselective Ni-Catalyzed Protecting-Group-Free 2,2'-Biphenol Synthesis and Mechanistic Insights

The utilization of readily available starting materials to produce useful molecules is often challenged by selectivity issues. In this study, a Ni-catalyzed protecting-group-free C-C coupling protocol is described for the efficient synthesis of 2,2'-biphenol derivatives. Its remarkable chemoselectivity control ability, wide substrate scope, and excellent functional group tolerance highlight this newly developed strategy. Detailed mechanistic studies have demonstrated that potassium tert-butoxide acts as a critical agent to prevent the occurrence of protonation events.

Intermolecular diastereoselective annulation of azaarenes into fused N-heterocycles by Ru(II) reductive catalysis

Derivatization of azaarenes can create molecules of biological importance, but reductive functionalization of weakly reactive azaarenes remains a challenge. Here the authors show a dearomative, diastereoselective annulation of azaarenes, via ruthenium(II) reductive catalysis, proceeding with excellent selectivity, mild conditions, and broad substrate and functional group compatibility. Mechanistic studies reveal that the products are formed via hydride transfer-initiated β-aminomethylation and α-arylation of the pyridyl core in the azaarenes, and that paraformaldehyde serves as both the C1-building block and reductant precursor, and the use of Mg(OMe)2 base plays a critical role in determining the reaction chemo-selectivity by lowering the hydrogen transfer rate. The present work opens a door to further develop valuable reductive functionalization of unsaturated systems by taking profit of formaldehyde-endowed two functions.

Four- and five-coordinate nickel(ii) complexes bearing new diphosphine-phosphonite and triphosphine-phosphite ligands: catalysts for N-alkylation of amines

The reaction of Ph2PCH2OH with PhPCl2 and PCl3 in the presence of Et3N afforded new phosphonite compounds PhP(OCH2PPh2)21 and P(OCH2PPh2)32, respectively. The reaction between 1 and [NiCl2(DME)] in dichloromethane gave the five-coordinate complex [NiCl2(1-κ3 P,P,P)] 3. Conversely, 1 reacts with [NiCl2(DME)] in the presence of NH4PF6 in dichloromethane to yield the four coordinate ionic complex [NiCl(1-κ3 P,P,P)][PF6] 4. The reactions between 1, [NiCl2(DME)] and KPF6 in the presence of RNC (R = Xylyl, t Bu and iPr) in dichloromethane yielded the five coordinate monocationic [NiCl(1-κ3 P,P,P)(RNC)][PF6] (R = Xylyl) and dicationic [Ni(1-κ3 P,P,P)(RNC)2][PF6]2 (R = t Bu and iPr) complexes, respectively. The analogous reaction of 2 with [NiCl2(DME)] in the presence of KPF6 gave complex [NiCl(2-κ4 P,P,P,P)][PF6], 8. The structures of all complexes were determined by single crystal X-ray diffraction studies and supported by spectroscopic methods. To demonstrate their catalytic application, N-alkylation reactions between primary aryl amines, benzyl and 4-methoxy benzyl alcohols were found to proceed smoothly in the presence of 2.5 mol% of complexes bearing ligand 1 and <0.5 mmol of KOBu t in toluene at 140 °C. The C-N coupled products were formed in very good yields. Its substrate scope includes sterically encumbered, heterocyclic amines and aliphatic alcohol.

Iridium/graphene nanostructured catalyst for the N-alkylation of amines to synthesize nitrogen-containing derivatives and heterocyclic compounds in a green process

A facile iridium/graphene-catalyzed methodology providing an efficient synthetic route for C-N bond formation is reported. This catalyst can directly promote the formation of C-N bonds, without pre-activation steps, and without solvents, alkalis and other additives. This protocol provides a direct N-alkylation of amines using a variety of primary and secondary alcohols with good selectivity and excellent yields. Charmingly, the use of diols resulted in intermolecular cyclization of amines, and such products are privileged structures in biologically active compounds. Two examples illustrate the advantages of this catalyst in organic synthesis: the tandem catalysis to synthesize hydroxyzine, and the intermolecular cyclization to synthesize cyclizine. Water is the only by-product, which makes this catalytic process sustainable and environmentally friendly.

N-Alkylation of organonitrogen compounds catalyzed by methylene-linked bis-NHC half-sandwich ruthenium complexes

An efficient ruthenium-catalyzed N-alkylation of amines, amides and sulfonamides has been developed employing novel pentamethylcyclopentadienylruthenium(II) complexes bearing the methylene linked bis(NHC) ligand bis(3-methylimidazol-2-ylidene)methane. The acetonitrile complex 2 has proven particularly effective with a broad range of substrates with low catalyst loading (0.1-2.5 mol%) and high functional group tolerance under mild conditions. A total of 52 N-alkylated organonitrogen compounds including biologically relevant scaffolds were synthesized from (hetero)aromatic and aliphatic amines, amides and sulfonamides using alcohols or diols as alkylating agents in up to 99% isolated yield, even on gram-scale reactions. In the case of sulfonamides, it is the first example of N-alkylation employing a transition-metal complex bearing NHC ligands.

Synthesis of acridinones via palladium-catalyzed reductive annulation of 2-nitrobenzaldehydes and resorcinols

Through a palladium-catalyzed reductive annulation reaction of resorcinols and 2-nitrobenzaldehydes, reported is a new synthesis of acridinones with the features of operational simplicity, broad substrate scope, and readily available feedstocks.

Redox-Neutral Dehydrogenative Cross-Coupling of Alcohols and Amines Enabled by Nickel Catalysis

Presented herein is a facile and straightforward synthetic method for the construction of amides via Ni/NHC-catalyzed amidation of alcohols with amines. The strategy exhibits various advantages over existing methods, including...

Disarming the alkoxide trap to access a practical FeCl3 system for borrowing-hydrogen N-alkylation

Disarming the alkoxide trap using an in situ reduction strategy to access a practical FeCl3 and N-heterocyclic carbene system for borrowing-hydrogen N-alkylation.

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.

Coordinatively Unsaturated Hf-MOF-808 Prepared via Hydrothermal Synthesis as a Bifunctional Catalyst for the Tandem N-Alkylation of Amines with Benzyl Alcohol

The modulated hydrothermal (MHT) synthesis of an active and selective Hf-MOF-808 material for the N-alkylation reaction of aniline with benzyl alcohol under base-free mild reaction conditions is reported. Through kinetic experiments and isotopically labeled NMR spectroscopy studies, we have demonstrated that the reaction mechanism occurs via borrowing hydrogen (BH) pathway, in which the alcohol dehydrogenation is the limiting step. The high concentration of defective -OH groups generated on the metallic nodes through MHT synthesis enhances the alcohol activation, while the unsaturated Hf⁴⁺, which acts as a Lewis acid site, is able to borrow the hydrogen from the methylene position of benzyl alcohol. This fact makes this material at least 14 times more active for the N-alkylation reaction than the material obtained via solvothermal synthesis. The methodology described in this work could be applied to a wide range of aniline and benzyl alcohol derivates, showing in all cases high selectivity toward the corresponding N-benzylaniline product. Finally, Hf-MOF-808, which acts as a true heterogeneous catalyst, can be reused in at least four consecutive runs without any activity loss.

Heterogenizing a Homogeneous Nickel Catalyst Using Nanoconfined Strategy for Selective Synthesis of Mono- and 1,2-Disubstituted Benzimidazoles

A homogeneous Ni-phenanthroline catalyst was successfully immobilized into the cavities of a metal-organic framework, ZIF-8. The as-synthesized heterogeneous catalyst, Ni-Phen@ZIF, represents the first MOF based catalyst that enables dehydrogenative coupling of alcohols with aromatic diamines for selective synthesis of both mono- and 1,2-disubstituted benzimidazoles. The catalyst survived under harsh basic conditions, characterized by SEM, TEM, BET, PXRD, and EDX elemental mappings. The presence of the nanoconfined Ni-phenanthroline complex and the formation of extra Lewis acid sites during catalysis in the Ni-Phen@ZIF structure, confirmed by TPD analysis and kinetic experiments, might be responsible for higher activity and selectivity.

Reductive electrophilic C-H alkylation of quinolines by a reusable iridium nanocatalyst

The incorporation of a coupling step into the reduction of unsaturated systems offers a desirable way for diverse synthesis of functional molecules, but it remains to date a challenge due to the difficulty in controlling the chemoselectivity. Herein, by developing a new heterogeneous iridium catalyst composed of Ir-species (Ir^δ+) and N-doped SiO₂/TiO₂ support (Ir/N-SiO₂/TiO₂), we describe its application in reductive electrophilic mono and dialkylations of quinolines with various 2- or 4-functionalized aryl carbonyls or benzyl alcohols by utilizing renewable formic acid as the reductant. This catalytic transformation offers a practical platform for direct access to a vast range of alkyl THQs, proceeding with excellent step and atom-efficiency, good substrate scope and functional group tolerance, a reusable catalyst and abundantly available feedstocks, and generation of water and carbon dioxide as by-products. The work opens a door to further develop more useful organic transformations under heterogeneous reductive catalysis.

By developing a heterogeneous iridium catalyst composed of a N-doped SiO₂/TiO₂ support and Ir-species (Ir/N-SiO₂/TiO₂), its application in reductive electrophilic alkylation of quinolines with various aryl carbonyls or benzyl alcohols is presented.

Recent advances in transition metal-catalyzed (1,n) annulation using (de)-hydrogenative coupling with alcohols

(1,n) annulation reactions using (de)-hydrogenative coupling with alcohols or diols represent a straightforward technique for the synthesis of cyclic moieties. Utilization of such renewable resources for chemical transformations in a one-pot manner is the main focus, which avoids generation of stoichiometric waste. Application of such (1,n) annulation approaches drives the catalysis research in a more sustainable way and generates dihydrogen and water as by-products. This feature article highlights the recent (from 2015 to March 2021) progress in the synthesis of stereo-selective cycloalkanes and cycloalkenes, saturated and unsaturated N-heterocycles (cyclic amine, imide, lactam, tetrahydro β-carboline, quinazoline, quinazolinone, 1,3,5-triazines etc.) and other N-heterocycles with the formation of multiple bonds in a one pot operation. Mechanistic studies, new catalytic approaches, and synthetic applications including drug synthesis and post-drug derivatization, scope, and limitations are discussed.

Selective construction of fused heterocycles by an iridium-catalyzed reductive three-component annulation reaction

Catalytic conversion of ubiquitously distributed but less reactive N-heteroarenes into functional products remains to date a challenge. Here, through an initial pretreatment of N-heteroarenes with alkyl bromide, we describe a syn-selective construction of functional fused heterocycles via iridium catalyzed reductive annulation of N-heteroarenium salts with formaldehyde and cyclic 1,3-diketones or 4-hydroxycoumarins, proceeding with broad substrate scope, good functional group compatibility, readily available feedstocks, and high step and atom efficiency.

Recent advances in nickel-catalyzed C-C and C-N bond formation via HA and ADC reactions

In recent times, earth-abundant 3d-transition-metal catalysts have attracted much attention in contemporary catalysis. They have been widely employed as suitable alternatives to their counterparts noble metals. In particular, nickel catalysts provide distinctive redox properties; thus, their efficiency in sustainable organic transformations is manifold. In this review article, recent advances in nickel-catalyzed hydrogen auto-transfer (HA) and acceptorless dehydrogenative coupling (ADC) reactions for the construction of C-C and C-N bonds have been discussed.

[(PPh3)2NiCl2]-Catalyzed C-N Bond Formation Reaction via Borrowing Hydrogen Strategy: Access to Diverse Secondary Amines and Quinolines

Commercially available [(PPh₃)₂NiCl₂] was found to be an efficient catalyst for the mono-N-alkylation of (hetero)aromatic amines, employing alcohols to deliver diverse secondary amines, including the drug intermediates chloropyramine (5b) and mepyramine (5c), in excellent yields (up to 97%) via the borrowing hydrogen strategy. This method shows a superior activity (TON up to 10000) with a broad substrate scope at a low catalyst loading of 1 mol % and a short reaction time. Further, this strategy is also successful in accessing various quinoline derivatives following the acceptorless dehydrogenation pathway.