Mild, Metal-Free and Protection-Free Transamidation of N-Acyl-2-piperidones to Amino Acids, Amino Alcohols and Aliphatic Amines and Esterification of N-Acyl-2-piperidones

Ring Opening of N-Acyl Lactams Using Nickel-Catalyzed Transamidation

We successfully developed a nickel-catalyzed transamidation method for the ring opening of N-acyl lactams. The method involves a reaction between N-benzoylpyrrolidin-2-one derivatives and aniline derivatives, with Ni(PPh3)2Cl2 serving as the catalyst, 2,2'-bipyridine as the ligand, and manganese as the reducing agent. This reaction led to the formation of ring-opening-amidated products in good yields. Notably, the method exhibited excellent efficiency for producing the corresponding ring-opening transamidation products for various ring sizes, including four-, five-, six-, seven-, and eight-membered ring lactams.

Reductive cross-coupling of N-acyl pyrazole and nitroarene using tetrahydroxydiboron: synthesis of secondary amides

We report on a new method for the synthesis of amides using acyl pyrazoles and nitroarenes under reducing conditions. It was found that acyl pyrazoles react with organo-nitro compounds in the presence of B2(OH)4, giving the corresponding amides in good yields. We demonstrated that benzoyl pyrazoles having various substituents and nitroarenes with different substituents can be used to produce a range of N-substituted benzamides. The method shows good functional group tolerance and has potential application in the synthesis of a variety of organic molecules.

B2(OH)4-Mediated Reductive Transamidation of N-Acyl Benzotriazoles with Nitro Compounds En Route to Aqueous Amide Synthesis

We herein developed a reductive transamidation reaction between N-acyl benzotriazoles (AcBt) and organic nitro compounds or NaNO₂ under mild conditions. This protocol employed the stable and readily available B₂(OH)₄ as the reducing agent and H₂O as the ideal solvent. N-Deuterated amides can be synthesized when conducting the reaction in D₂O. A reasonable reaction mechanism involving bond metathesis between the AcBt amide and amino boric acid intermediate was proposed to explain the unique nature of AcBt.

Amide N-C Bond Activation: A Graphical Overview of Acyl and Decarbonylative Coupling

This Graphical Review provides an overview of amide bond activation achieved by selective oxidative addition of the N-C(O) acyl bond to transition metals and nucleophilic acyl addition, resulting in acyl and decarbonylative coupling together with key mechanistic details pertaining to amide bond distortion underlying this reactivity manifold.

Highly Chemoselective Transamidation of Unactivated Tertiary Amides by Electrophilic N-C(O) Activation by Amide-to-Acyl Iodide Re-routing

The challenging transamidation of unactivated tertiary amides has been accomplished via cooperative acid/iodide catalysis. Most crucially, the method provides a novel manifold to re-route the reactivity of unactivated N,N-dialkyl amides through reactive acyl iodide intermediates, thus reverting the classical order of reactivity of carboxylic acid derivatives. This method provides a direct route to amide-to-amide bond interconversion with excellent chemoselectivity using equivalent amounts of amines. The combination of acid and iodide has been identified as the essential factor to activate the amide C-N bond through electrophilic catalytic activation, enabling the production of new desired transamidated products with wide substrate scope of both unactivated amides and amines, including late-stage functionalization of complex APIs (>80 examples). We anticipate that this powerful activation mode of unactivated amide bonds will find broad-ranging applications in chemical synthesis.

Nickel-Catalyzed Reductive Cross-Coupling of N-Acyl and N-Sulfonyl Benzotriazoles with Diverse Nitro Compounds: Rapid Access to Amides and Sulfonamides

Herein we report a Ni-catalyzed reductive transamidation of conveniently available N-acyl benzotriazoles with alkyl, alkenyl, and aryl nitro compounds, which afforded various amides with good yields and a broad substrate scope. The same catalytic reaction conditions were also applicable for N-sulfonyl benzotriazoles, which could undergo smooth reductive coupling with nitroarenes and nitroalkanes to afford the corresponding sulfonamides.

Synthesis of the Proposed Structures of Parvistemoamide and Their Transformations to Stemoamide Derivatives

The proposed structures of parvistemoamide have been achieved by macrolactamization, but none of the characterization data of synthetic samples matched with those of the natural sample. The transformation of the highly strained 10-membered lactam ring in parvistemoamide into the pyrrolo[1,2-a]-azepine nucleus in stemoamide is accomplished for the first time by either transannular cyclization or Pilli's transformation. This research may promote the total synthesis of other more complex stemoamide-type or medium-sized-ring-containing Stemona alkaloids.

Disruption of redox homeostasis with synchronized activation of apoptosis highlights the antifilarial efficacy of novel piperine derivatives: An in vitro mechanistic approach

A series of novel piperine derivatives were synthesized with high yield and were evaluated for its antifilarial potential against the bovine filarial parasite Setaria cervi. Among 21 (3a-3u) compounds screened, three of them (3k, 3l, 3s) showed significant potential against all the developmental stages (oocytes, microfilariae and adult) of the filarial worm in time and dose dependent manner. 3l showed the highest efficacy among the selected three compounds. These three compounds were further evaluated for both in vitro and in vivo toxicity analyses which further fortified the benign nature of the selected compounds. The antifilarial activities they exhibited were clearly fuelled through disparity of the internal redox homeostasis as evidenced from the alterations in the enzymatic and non-enzymatic antioxidants level which ultimately shifted towards activation of pro-apoptotic signaling cascade eventually leading to the death of the parasites. The ability of the compound 3l to bind thioredoxin reductase and CED-3 protein are the key findings of this study. The present study supported with several biological experiments is therefore a maiden report on the antifilarial effectiveness of these novel piperine derivatives.

Metal-free transamidation of benzoylpyrrolidin-2-one and amines under aqueous conditions

N-Acyl lactam amides, such as benzoylpyrrolidin-2-one, benzoylpiperidin-2-one, and benzoylazepan-2-one reacted with amines in the presence of DTBP and TBAI to afford the transamidated products in good yields. The reactions were conducted under aqueous conditions and good functional group tolerance was achieved. Both aliphatic and aromatic primary amines displayed good activity under metal-free conditions. A radical reaction pathway is proposed.

Amide Synthesis through the In Situ Generation of Chloro- and Imido-Phosphonium Salts

We describe a methodology for the amidation of carboxylic acids by generating phosphonium salts in situ from N-chlorophthalimide and triphenylphosphine. Aliphatic, benzylic, and aromatic carboxylic acids can be transformed into their amide counter parts using primary and secondary amines. This functional group interconversion is achieved at room temperature in good to excellent yields. Mechanistic work shows the in situ formation of chloro- and imido-phosphonium salts that react as activating agents for carboxylic acids and generate an acyloxy-phosphonium species.

Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

In the past several years, tremendous advances have been made in non-classical routes for amide bond formation that involve transamidation and amidation reactions of activated amides and esters. These new methods enable the formation of extremely valuable amide bonds via transition-metal-catalyzed, transition-metal-free, or metal-free pathways by exploiting chemoselective acyl C–X (X = N, O) cleavage under mild conditions. In a broadest sense, these reactions overcome the formidable challenge of activating C–N/C–O bonds of amides or esters by rationally tackling nN → π*C=O delocalization in amides and nO → π*C=O donation in esters. In this account, we summarize the recent remarkable advances in the development of new methods for the synthesis of amides with a focus on (1) transition-metal/NHC-catalyzed C–N/C–O bond activation, (2) transition-metal-free highly selective cleavage of C–N/C–O bonds, (3) the development of new acyl-transfer reagents, and (4) other emerging methods.

1 Introduction

2 Transamidation of Amides

2.1 Transamidation by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)

2.2 Transition-Metal-Free Transamidation via Tetrahedral Intermediates

2.3 Reductive Transamidation

2.4 New Acyl-Transfer Reagents

2.5 Tandem Transamidations

3 Amidation of Esters

3.1 Amidation of Esters by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)

3.2 Transition-Metal-Free Amidation of Esters via Tetrahedral Intermediates

3.3 Reductive Amidation of Esters

4 Transamidations of Amides by Other Mechanisms

5 Conclusions and Outlook

New Efficient Eco-Friendly Supported Catalysts for the Synthesis of Amides with Antioxidant and Anti-Inflammatory Properties

A new environmentally friendly approach for the synthesis of idrocilamide (1), a marketed myorelaxant and anti-inflammatory agent, is reported herein. The synthetic strategy involves a solvent-free aminolysis reaction catalyzed by zinc-containing species (ZnCl₂ , montmorillonite K10 (MK10) impregnated with ZnCl₂ or eco-catalysts). The latter have been prepared from the aerial parts of Lolium perenne L. plants grown on contaminated soils from northern France without and with thermal activation at 120 °C and supported on MK10 (Ecocat1 and Ecocat2, respectively). The best aminolysis catalysts in the current study (ZnCl₂ and Ecocat2) were selected for additional aminolyses. Compared to ZnCl₂ , Ecocat2 had the advantage of being reusable over five test runs and constituted a sustainable catalyst allowing a green route to idrocilamide. Synthesized derivatives 1-4, 6 and 9 were first evaluated for their effect on reactive oxygen species (ROS) generation from macrophages and displayed antioxidant properties by preventing ROS production. Next, the analysis of the effect of molecules 1-4, 6 and 9 on macrophage migration between epithelial cells to human opportunistic fungus Candida albicans indicated that molecules 2-4, 6 and 9 exert anti-inflammatory properties via reducing macrophage migration while the parent idrocilamide (1) did not show any significant effect. This work opens the way for the discovery of new analogues of idrocilamide with improved properties.

Coupling of amides with ketones via C–N/C–H bond cleavage: a mild synthesis of 1,3-diketones

Amides react with enolizable ketones to give 1,3-diketones via C–N cleavage of amides and deprotonation of ketones.