A Convenient and General Iron-Catalyzed Reduction of Amides to Amines

Phenalenyl-ruthenium synergism for effectual catalytic transformations of primary amines to amides

The synthesis of amides holds great promise owing to their impeccable contributions as building blocks for highly valued functional derivatives. Herein, we disclose the design, synthesis and crystal structure of a mixed-ligand ruthenium(II) complex, [Ru(η6-Cym)(O,O-PLY)Cl], (1) where Cym = 1-isopropyl-4-methyl-benzene and O,O-PLY = deprotonated form of 9-hydroxy phenalenone (HO,O-PLY). The complex catalyzes the aerobic oxidation of various primary amines (RCH2NH2) to value-added amides (RCONH2) with excellent selectivity and efficiency under relatively mild conditions with common organic functional group tolerance. Structural, electrochemical, spectroscopic, and computational studies substantiate that the synergism between the redox-active ruthenium and π-Lewis acidic PLY moieties facilitate the catalytic oxidation of amines to amides. Additionally, the isolation and characterization of key intermediates during catalysis confirm two successive dehydrogenation steps leading to nitrile, which subsequently transform to the desired amide through hydration. The present synthetic approach is also extended to substitution-dependent tuning at PLY to tune the electronic nature of 1 and to assess substituent-mediated catalytic performance. The effect of substitution at the PLY moiety (5th position) leads to structural isomers, which were further evaluated for the catalytic transformations of amine to amides under similar reaction conditions.

Copper-Catalyzed Borrowing Hydrogen Reaction for α-Alkylation of Amides with Alcohols

We report the first example of copper-catalyzed α-alkylation of acetamides with alcohols via a borrowing hydrogen strategy. Catalyzed by the in situ-generated copper particles, acetamides and various substituted benzyl or alkyl alcohols were transformed into functionalized amides in good yields with excellent selectivity. Compared with previous work, this process is simple using commercially available Cu(OAc)2 as a precatalyst, without an additional ligand or a metal complex, and easier. Mechanistic studies revealed that aldehyde and α,β-unsaturated amides were the intermediates of this reaction and also disclosed the role of copper in alcohol dehydrogenation and C═C bond hydrogenation.

Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to α,β-Unsaturated Lactams: Enantioselective Construction of All-Carbon Quaternary Stereocenters in Saturated Nitrogen-Containing Heterocycles

Stereogenic nitrogen-containing heterocycles are ubiquitous in natural products and pharmaceutical compounds, but methods for their enantioselective construction have remained elusive. We report a general method for the asymmetric conjugate addition of arylboronic acids to β-alkyl/aryl α,β-unsaturated lactams that affords chiral β,β-disubstituted lactams. The transformation is operationally simple and air- and moisture-tolerant and uses a commercially available (S)-t-Bu-PyOx ligand. The method is high-yielding (up to 95% yield) and enantioselective (up to 97% ee) for a wide range of arylboronic acids and α,β-unsaturated lactams, including those with different ring sizes.

Mild Divergent Semireductive Transformations of Secondary and Tertiary Amides via Zirconocene Hydride Catalysis

The mild catalytic partial reduction of amides to imines has proven to be a challenging synthetic transformation, with many transition metals directly reducing these substrates to amines. Herein, we report a mild, catalytic method for the semireduction of both secondary and tertiary amides via zirconocene hydride catalysis. Utilizing just 5 mol % of Cp2ZrCl2, the reductive deoxygenation of secondary amides is demonstrated to furnish a diverse array of imines in up to 94% yield with excellent chemoselectivity and without the need for glovebox handling. Moreover, a novel reductive transamination of tertiary amides is also achievable when the catalytic protocol is carried out in the presence of a primary amine at room temperature, providing access to an expanded assortment of imines in up to 98% yield. Through slight procedural tuning, the single-flask conversion of amides to imines, aldehydes, amines or enamines is feasible, including multicomponent syntheses.

Palladium-Catalyzed Desulfurative Hiyama Coupling of Thioureas to Achieve Amides via Selective C–N Bond Cleavage

Palladium-catalyzed Hiyama coupling of active thioureas via selective C–N bond cleavage is reported. Notably, the new approach employed active thioureas as coupling partners in the presence of arylsilanes to give amides in good yield. Further, this strategy, which utilized CuF2 as a key oxidant and activator, afforded various amide products under mild conditions and an easy to handle procedure without extra base.

Silver(i)-catalyzed oxidative coupling of hydrosilanes with DMF to symmetrical and unsymmetrical disiloxanes

An alternative route to symmetrical and unsymmetrical disiloxanes, utilizing a 0.5% AgNTf2 catalyst to enable oxidative coupling of hydrosilanes with DMF as an oxygen source, is reported.

Hydroborative reduction of amides to amines mediated by La(CH2C6H4NMe2-o)3

La(CH2C6H4NMe2-o)3/HBpin is an efficient catalytic system for the deoxygenative reduction of primary, secondary and tertiary amides to amines.

Hydrosilylative reduction of primary amides to primary amines catalyzed by a terminal [Ni-OH] complex

A terminal [Ni-OH] complex 1, supported by triflamide-functionalized NHC ligands, catalyzes the hydrosilylative reduction of a range of primary amides into primary amines in good to excellent yields under base-free conditions with key functional group tolerance. Catalyst 1 is also effective for the reduction of a variety of tertiary and secondary amides. In contrast to literature reports, the reactivity of 1 towards amide reduction follows an inverse trend, i.e., 1° amide > 3° amide > 2° amide. The reaction does not follow a usual dehydration pathway.

Total Synthesis of Mycocyclosin and the Herqulines

Since the first reports of their isolation, mycocyclosin and the herquline family of natural products have attracted interest from the synthetic community for their uniquely strained macrocyclic architectures. This review describes the attempted and successful total syntheses of these natural products and provides a summary of the strategies developed in the years since their isolation.

1 Introduction

2 Biosynthesis

3 Early Studies

4 Total Synthesis of Mycocyclosin

5 Overview

6 Wood’s Total Syntheses of Herqulines B and C

7 Baran’s Total Syntheses of Herqulines B and C

8 Schindler’s Total Syntheses of Herqulines B and C

9 Conclusions

Biorenewable carbon-supported Ru catalyst for N-alkylation of amines with alcohols and selective hydrogenation of nitroarenes

A renewable carbon-supported Ru catalyst (Ru/PNC-700) facilely prepared via simple impregnation followed by the pyrolysis process for N-alkylation of anilines with benzyl alcohol and chemoselective hydrogenation of nitroarenes.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Recent advances in liquid hydrosilane-mediated catalytic N-formylation of amines with CO2

Carbon dioxide is an ideal raw material for the synthesis of complex organic compounds because of its rich, non-toxic, and good physical properties. It is of great significance to transform CO₂ into valuable fine chemicals and develop a green sustainable cycle of carbon surplus. Based on hydrosilane as a reducing agent, this work summarizes the recent applications of reductive amidation of CO₂ using different catalysts such as organocatalysts, ionic liquids (ILs), salts, transition metal complexes, and solvents. The main factors affecting the reductive amidation of CO₂ and the possible reaction mechanism are discussed. Moreover, the future orientation and catalytic systems of the formylation of amines with CO₂ and hydrosilane are prospected.

This review depicts different types of catalyst systems developed for upgrading of amines and carbon dioxide into N-formylated products in the presence of hydrosilane, with attention on reaction mechanism and process optimization.

Homoleptic Bis(trimethylsilyl)amides of Yttrium Complexes Catalyzed Hydroboration Reduction of Amides to Amines

Homoleptic lanthanide complex Y[N(TMS)₂]₃ is an efficient homogeneous catalyst for the hydroboration reduction of secondary amides and tertiary amides to corresponding amines. A series of amides containing different functional groups such as cyano, nitro, and vinyl groups were found to be well-tolerated. This transformation has also been nicely applied to the synthesis of indoles and piribedil. Detailed isotopic labeling experiments, control experiments, and kinetic studies provided cumulative evidence to elucidate the reaction mechanism.

Zn(ii)@TFP-DAQ COF: an efficient mesoporous catalyst for the synthesis of N-methylated amine and carbamate through chemical fixation of CO2

Selective N-methylation and carbamate formation reactions were demonstrated via the chemical incorporation of CO₂ using a Zn-loaded TFP-DAQ COF (covalent organic framework) as an active catalyst under mild reaction conditions.

Double Addition of Alkynyllithium Reagents to Amides/Lactams: A Direct and Flexible Synthesis of 3-Amino-1,4-diynes Bearing an Aza-Quaternary Carbon Center

An efficient and mild protocol for the direct and flexible synthesis of 3-amino-1,4-diynes bearing an aza-quaternary carbon from tertiary amides and lactams has been established. The one-pot method consists of in situ activation of amides with trifluoromethanesulfonic anhydride, followed by double addition of alkynyllithium reagents at a concentration of 0.5 mol·L^-1 in dichloromethane. This constitutes an extension of the method of direct reductive bisalkylation of amides that allows both employing alkynyllithium reagents as the first-addition nucleophiles and incorporating an alkynyl group as the first-introduced group.

Iron-Catalysed Reductive Amination of Carbonyl Derivatives with ω-Amino Fatty Acids to Access Cyclic Amines

An efficient method for the reductive amination of carbonyl derivatives with ω-amino fatty acids catalysed by an iron complex Fe(CO)₄ (IMes) [IMes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] by means of hydrosilylation was developed. A variety of pyrrolidines, piperidines and azepanes were selectively synthesised in moderate-to-excellent yields (36 examples, 47-97 % isolated yield) with a good functional group tolerance.

Base Metal Catalysts for Deoxygenative Reduction of Amides to Amines

The development of efficient methodologies for production of amines attracts significant attention from synthetic chemists, because amines serve as essential building blocks in the synthesis of many pharmaceuticals, natural products, and agrochemicals. In this regard, deoxygenative reduction of amides to amines by means of transition-metal-catalyzed hydrogenation, hydrosilylation, and hydroboration reactions represents an attractive alternative to conventional wasteful techniques based on stoichiometric reductions of the corresponding amides and imines, and reductive amination of aldehydes with metal hydride reagents. The relatively low electrophilicity of the amide carbonyl group makes this transformation more challenging compared to reduction of other carbonyl compounds, and the majority of the reported catalytic systems employ precious metals such as platinum, rhodium, iridium, and ruthenium. Despite the application of more abundant and environmentally benign base metal (Mn, Fe, Co, and Ni) complexes for deoxygenative reduction of amides have been developed to a lesser extent, such catalytic systems are of great importance. This review is focused on the current achievements in the base-metal-catalyzed deoxygenative hydrogenation, hydrosilylation, and hydroboration of amides to amines. Special attention is paid to the design of base metal catalysts and the mechanisms of such catalytic transformations.

A BEt3-Base Catalyst for Amide Reduction with Silane

Reported herein is the development of a simple but practical catalytic system for the selective reduction of amides with hydrosilane or hydrosiloxane. Low-cost and readily available triethylborane (1.0 M in THF), in combination with a catalytic amount of an alkali metal base, was found to catalyze the reduction of all three amide classes (tertiary, secondary, and primary amides) to form amines under mild conditions. In addition, the selective transformation of secondary amides to aldimines and primary amides to nitriles can also be achieved by using a proper combination of BEt₃ and base. The scope of these BEt₃-base-catalyzed amide hydrosilylation reactions has been explored in depth. Preliminary results of mechanistic studies suggest a modified Piers' silane Si-H···B activation mode wherein the hydride abstraction by BEt₃ is promoted by the coordination of an alkoxide or hydroxide anion to the Si center.

Selective reduction of formamides to O-silylated hemiaminals or methylamines with HSiMe2Ph catalyzed by iridium complexes

The reaction of (4-methyl-pyridin-2-iloxy)ditertbutylsilane (NSitBu-H, 1) with [IrCl(coe)2]2 affords the iridium(iii) complex [Ir(H)(Cl)(κ2-NSitBu)(coe)] (2), which has been fully characterized including X-ray diffraction studies. The reaction of 2 with AgCF3SO3 leads to the formation of species [Ir(H)(CF3SO3)(κ2-NSitBu)(coe)] (3). The iridium complexes 2 and 3 are effective catalysts for the reduction of formamides with HSiMe2Ph. The selectivity of the reduction process depends on the catalyst. Thus, by using complex 2, with a chloride ancillary ligand, it has been possible to selectively obtain the corresponding O-silylated hemiaminal by reaction of formamides with one equivalent of HSiMe2Ph, while complex 3, with a triflate ligand instead of chloride, catalyzed the selective reduction of formamides to the corresponding methylamine.

Haridasan R, Das A, Ahmed J, Mandal SK. Primary amides to amines or nitriles: a dual role by a single catalyst

We report the first earth abundant single mononuclear Mn(iii) complex which can selectively and catalytically transform primary amides to nitriles as well as reduce primary amides to amines.

Palladium doping of In2O3 towards a general and selective catalytic hydrogenation of amides to amines and alcohols

The first general heterogeneous hydrogenation of amides to amines and alcohols is performed under additive-free conditions and without product de-aromatization by applying a Pd-doped In₂O₃ catalyst.

A comparative analysis of hydrosilative amide reduction catalyzed by first-row transition metal (Mn, Fe, Co, and Ni) N-phosphinoamidinate complexes

Screening reveals (PN)Ni(x) pre-catalysts to be effective for the hydrosilative reduction of amides under mild conditions.

Hydride-catalyzed selectively reductive cleavage of unactivated tertiary amides using hydrosilane

The first hydride-catalyzed reductive cleavage of tertiary amides using the hydrosilane as reducing reagent has been developed. This transition-metal-free process may offer a versatile alternative to current systems for the selective reductive cleavage of amides.