Intramolecular Reductive Amidation of Unactivated Esters with Nitroarenes: A Telescoped Synthesis of Tetrahydropyrrolo/Pyrido[1,2-a]quinoxalinones

A reductive amidation of unactivated esters with nitroarenes, a key step in the telescopic synthesis of tetrahydropyrrolo[1,2-a]quinoxalinones and tetrahydropyrido[1,2-a]quinoxalinones, is reported. The process involves an intermolecular base-mediated SNAr reaction, followed by intramolecular reductive amidation employing sodium dithionite. The substrate scope coupled with the demonstration of the synthesis of pharmaceuticals is reported. The key features include nitro reduction at room temperature, easy purification without chromatography, amidation of unactivated esters without any externally added activating agent, and a telescopic process.

A Guide for Mono-Selective N-Methylation, N-Ethylation, and N-n-Propylation of Primary Amines, Amides, and Sulfonamides and Their Applicability in Late-Stage Modification

This review provides a comprehensive overview of mono-alkylation methodologies targeting crucial nitrogen moieties - amines, amides, and sulfonamides - found in organic building blocks and pharmaceuticals. Emphasizing the intersection of chemical precision with drug discovery, the central challenge addressed is achieving one-pot mono-selective short-chain N-alkylations (methylations, ethylations, and n-propylations), preventing undesired overalkylation. Additionally, sustainable, safe, and benign alternatives to traditional alkylating agents, including alcohols, carbon dioxide, carboxylic acids, nitriles, alkyl phosphates, quaternary ammonium salts, and alkyl carbonates, are explored. This review, categorized by the nature of the alkylating agent, aids researchers in selecting suitable methods for mono-selective N-alkylation.

Cobalt nanoparticle-catalysed N-alkylation of amides with alcohols

A protocol for efficient N-alkylation of benzamides with alcohols in the presence of cobalt-nanocatalysts is described. Key to the success of this general methodology is the use of highly dispersed cobalt nanoparticles supported on carbon, which are obtained from the pyrolysis of cobalt(ii) acetate and o-phenylenediamine as a ligand at suitable temperatures. The catalytic material shows a broad substrate scope and good tolerance to functional groups. Apart from the synthesis of a variety of secondary amides (>45 products), the catalyst allows for the conversion of more challenging aliphatic alcohols and amides, including biobased and macromolecular amides. The practical applicability of the catalyst is underlined by the successful recycling and reusability.

Monoselective N-Methylation of Amides, Indoles, and Related Structures Using Quaternary Ammonium Salts as Solid Methylating Agents

We herein report the use of phenyl trimethylammonium iodide (PhMe₃NI) as a safe, nontoxic, and easy-to-handle reagent for an absolutely monoselective N-methylation of amides and related compounds as well as for the N-methylation of indoles. In addition, we expanded the method to N-ethylation using PhEt₃NI. The ease of operational setup, high yields of ≤99%, high functional group tolerance, and especially the excellent monoselectivity for amides make this method attractive for late-stage methylation of bioactive compounds.

Mild Amide N-Arylation Enabled by Nickel-Photoredox Catalysis

This paper describes a mild strategy to promote amide arylations. Photoinduced oxidation of a Ni(II) aryl amido intermediate is proposed to facilitate the challenging C-N reductive elimination step at moderate temperatures. Notably, the mildly basic conditions employed facilitate access to a broad scope including protected amino acids, heterocycles, phenols, and sterically hindered substituents. Hence, this work presents an attractive strategy to enable late-stage functionalization of pre-existing amide moieties in commercial drugs and natural products.

Mild Sustainable Amide Alkylation Protocol Enables a Broad Orthogonal Scope

Herein, the development of a mild sustainable protocol to couple primary alkyl chlorides and bromides with amides is described. In contrast to current methodologies, our system does not require the use of strongly basic conditions, high temperatures, or the addition of an organometallic catalyst, thereby enabling access to a remarkably orthogonal scope. K₃PO₄ is used to facilitate the formation of secondary and tertiary amides, which are ubiquitous scaffolds in bioactive molecules and natural products. Alkylated amide products are obtained in good to excellent yields, with no substantial limitations observed based on the steric and electronic properties of either coupling partner.

Easy S-Alkylation of Arylthioureas and 2-Mercaptobenzothiazoles Using Tetraalkylammonium Salts under Transition-Metal-Free Conditions

A highly-efficient and practical method for S-alkylation of arylthioureas was reported. Using tetraalkylammonium salts as alkylation reagents, a series of 68 S-substituted aryl-isothioureas were obtained in good to excellent yields under transition-metal-free conditions. The protocol features simple performance, broad functional group tolerance, good to excellent yields, and easily available starting materials, showing potential synthetic value for the preparation of diverse biologically or pharmaceutically active compounds.

Visible-Light-Promoted Fe(III)-Catalyzed N-H Alkylation of Amides and N-Heterocycles

The combination of the radical chemistry of ligand-to-metal charge transfer with metal catalysis by a single iron salt helps to realize the visible-light-promoted N-H alkylation of amides and N-heterocycles. A wide variety of amides and nitrogen-containing heterocycles were tolerated in our protocol to give N-alkylated products. The applicability of this protocol was further demonstrated by late-stage alkylation of N-H-containing pharmaceuticals. Moreover, N-H-alkylated α-amino tetrahydrofurans could be transformed into versatile ring-opened amino alcohols under reducing conditions. A mechanistic study revealed that hydrogen atom transfer by a tert-butoxyl radical and a chlorine radical was responsible for the activation of C(sp³)-H precursors.

Ru Doped Hydrotalcite Catalyzed Borrowing Hydrogen-Mediated N-Alkylation of Benzamides, Sulfonamides, and Dehydrogenative Synthesis of Quinazolinones

An efficient Ru doped hydrotalcite catalyzed N-alkylation of benzamides and sulfonamides with alcohols via borrowing hydrogen catalysis is illustrated. Various primary alcohols, including benzyl, heteroaryl, and aliphatic alcohols, were alkylated in good to excellent yields. To shed light on the mechanistic details, several control studies and deuterium labeling experiments were performed. Mechanistic studies underpin that the reaction is going via a borrowing hydrogen pathway rather than an S_N1 type mechanism. The reaction can be easily scaled up without any detrimental effect on the yield. The catalyst is also capable of synthesizing quinazolinone directly from 2-aminobenzamide and alcohols. Successful recyclability and high reactivity highlight the practical applicability of the catalyst.

A heteroditopic NHC and phosphine ligand supported ruthenium(ii)-complex: an effective catalyst for the N-alkylation of amides using alcohols

A heteroditopic Ru(ii)-bis-NHC complex in combination with dppe was developed as an effective catalyst system (0.2 mol% loading) for the N-alkylation of amides and selective mono-/di-alkylation of 4-aminobenzamide derivatives in excellent yields.

Direct N-alkylation of sulfur-containing amines

An efficient ruthenium-catalyzed method has been developed for the direct N-alkylation of sulfur-containing amines with alcohols, for the first time, by a step-economical and environmentally friendly hydrogen borrowing strategy. The present methodology features base-free conditions and broad substrate scope, with water being the only by-product. Moreover, this protocol has been applied to the synthesis of the pharmaceutical drug Quetiapine.

Monoacylation of Symmetrical Diamines in Charge Microdroplets

Monoacylation of symmetrical diamine is achieved when the primary α,ω-diamines (carbon numbers n = 3, 5 and 12) are diluted in ethyl acetate, and the resultant mixture is electrosprayed across a 10 mm distance in ambient air toward a mass spectrometer. The N-acylated product is formed in charged microdroplets without acidifying and activating agents and in the absence of heat. This result provided an insight into the orientation of the amines in the droplets, suggesting that the ester is activated to react with the amine at the droplet surface due to the high abundance of protons at the air-droplet interface.

Recent advances in pincer-nickel catalyzed reactions

Organometallic catalysts have played a key role in accomplishing numerous synthetically valuable organic transformations that are either otherwise not possible or inefficient. The use of precious, sparse and toxic 4d and 5d metals are an apparent downside of several such catalytic systems despite their immense success over the last several decades. The use of complexes containing Earth-abundant, inexpensive and less hazardous 3d metals, such as nickel, as catalysts for organic transformations has been an emerging field in recent times. In particular, the versatile nature of the corresponding pincer-metal complexes, which offers great control of their reactivity via countless variations, has garnered great interest among organometallic chemists who are looking for greener and cheaper alternatives. In this context, the current review attempts to provide a glimpse of recent developments in the chemistry of pincer-nickel catalyzed reactions. Notably, there have been examples of pincer-nickel catalyzed reactions involving two electron changes via purely organometallic mechanisms that are strikingly similar to those observed with heavier Pd and Pt analogues. On the other hand, there have been distinct differences where the pincer-nickel complexes catalyze single-electron radical reactions. The applicability of pincer-nickel complexes in catalyzing cross-coupling reactions, oxidation reactions, (de)hydrogenation reactions, dehydrogenative coupling, hydrosilylation, hydroboration, C-H activation and carbon dioxide functionalization has been reviewed here from synthesis and mechanistic points of view. The flurry of global pincer-nickel related activities offer promising avenues in catalyzing synthetically valuable organic transformations.

Recent advances in PIII-assisted deoxygenative reactions under photochemical or electrochemical conditions

The nucleophilic substitution reactions of hydroxyl groups are one of the most fundamental and widely spread transformations in organic chemistry. Among them, PIII-mediated deoxygenative nucleophilic substitution reactions, such as the Mitsunobu reaction, are frequently used strategies and often require stoichiometric oxidants to activate PIII reagents to induce the desired reactions. It has been illustrated that PIII reagents can be oxidized into the corresponding radical cations through single-electron oxidation by photocatalysis or electro-oxidation. These phosphine radical cations can react with alcohols or carboxylic acids to form the corresponding alkoxyphosphonium or acyloxyphosphonium intermediates, which are very reactive and easily get decomposed. The release of tri-substituted phosphine oxides as a driving force triggers the following nucleophilic substitution. This strategy does not require the use of stoichiometric oxidants and it eludes safety and stability problems. In this review, we summarise the recent advances and discoveries in PIII-assisted direct deoxygenative reactions under photochemical or electrochemical conditions.

Selective Methylation of Amides, N-Heterocycles, Thiols, and Alcohols with Tetramethylammonium Fluoride

We herein disclose the use of tetramethylammonium fluoride (TMAF) as a direct and selective methylating agent of a variety of amides, indoles, pyrroles, imidazoles, alcohols, and thiols. The method is characterized by operational simplicity, wide scope, and ease of purification. Our computational studies suggest a concerted methylation-deprotonation as the preferred reaction pathway.

Manganese-catalyzed direct C–C coupling of α-C–H bonds of amides and esters with alcohols via hydrogen autotransfer

Mn-catalyzed C-alkylation of amides and tert-butyl acetate using alcohols as alkylating agents is reported. This approach exhibits a broad substrate scope providing the C(α)-alkylated amides in good yields via hydrogen auto-transfer strategy.