Synthesis of 2-Quinolinones via a Hypervalent Iodine(III)-Mediated Intramolecular Decarboxylative Heck-Type Reaction at Room Temperature

Iodine-Catalyzed [5 + 1] Carbonylation of 2-Alkenyl/Pyrrolylanilines with CS2 as the Carbonylating Reagent

Novel metal-free iodine (I2)-catalyzed [5 + 1] carbonylation of 2-alkenyl/pyrrolylanilines with carbon disulfide (CS2) as the carbonylating reagent has been developed. This innovative method allows for the synthesis of valuable derivatives such as 4-aryl-2-quinolinones and pyrrolyl-fused quinoxalinones. Notably, this work represents the first instance where CS2 has been utilized as a carbonylating reagent source. The protocol demonstrates the utilization of various substrates, leading to diverse reactions that afford excellent yields under mild conditions. The method also shows good compatibility with functional groups present in the substrates, further enhancing its synthetic utility. Importantly, the developed reaction exhibits scalability, enabling gram-scale synthesis, and shows promise for the synthesis of druglike molecules. In this catalytic system, CS2 serves as the carbonyl source, while dimethyl sulfoxide plays multiple roles, including acting as an oxidant and a solvent. Mechanistic studies have been conducted to elucidate the underlying processes, with the formation of quinolone-2-thiones identified as crucial intermediates, facilitating the carbonylation annulation process.

PIDA-mediated Oxidative Decarboxylation of Oxamic Acids. The Role of Radical Acidity Enhancement

The PIDA-mediated oxidative decarboxylation of oxamic acids in the presence of alcohols is shown to afford the corresponding urethanes under thermal conditions. Computational and experimental mechanistic exploration allows to rationalize the different reactivity of PIDA as compared to related cyclic BI-OAc and highlights the importance of the enhanced acidity of the proton in the carbamoyl radical intermediate.

Metal -free PhI(OAc)2-oxidized decarboxylation of propiolic acids towards synthesis of α-acetoxy ketones and insights into general decarboxylation with DFT calculations

A metal-free oxidative decarboxylation reaction of propiolic acids mediated by hypervalent iodine(III) reagents is described. This decarboxylative C-O bond-forming reaction used a combination of (diacetoxyiodo)benzene and aromatic, heteroaromatic or aliphatic propiolic acids to give the corresponding α-acetoxy ketones. Preliminary mechanistic studies based on both DFT calculations and high-resolution mass spectroscopy (HRMS) suggested that the reaction proceeded through decarboxylation to form a propargyl iodide intermediate. This reaction provides an attractive alternative to existing methods for the exclusive synthesis of α-acyloxy ketones.

Oxamic acids: useful precursors of carbamoyl radicals

This review article describes the recent development in the chemistry of carbamoyl radicals generated from oxamic acids. This mild and efficient method compares well with previous methods of generation of these nucleophilic radicals. The oxidative decarboxylation of oxamic acids can be mediated through thermal, photochemical, electrochemical or photoelectrochemical means, generating carbamoyl radicals, which may further add to unsaturated systems to provide a broad range of important amides. Oxidative decarboxylation of oxamic acids also offers a straightforward entry for the preparation of urethanes, ureas, and thioureas.

Synthesis of N-Arylindoles from 2-Alkenylanilines and Diazonaphthalen-2(1H)-ones through Simultaneous Indole Construction and Aryl Introduction

In this paper, an efficient synthesis of N-arylindoles through the cascade reaction of 2-alkenylanilines with diazonaphthalen-2(1H)-ones is presented. Mechanistically, this reaction involves the generation of a Ru-carbene complex from diazonaphthalen-2(1H)-one, followed by carbene N-H bond insertion with 2-alkenylaniline, intramolecular cyclization, and oxidative aromatization. In this reaction, the Ru(II) complex acts as a multifunctional catalyst to promote not only the carbene formation but also the intramolecular cyclization and the dehydrogenative aromatization. Meanwhile, air acts as a green and cost-effective oxidant. To our knowledge, this is the first example in which N-arylindoles were synthesized through simultaneous introduction of the N-aryl unit and construction of the indole scaffold. Notable advantages of this method include readily accessible and halide-free substrates, additive-free reaction conditions, good efficiency, excellent atom economy, and compatibility with diverse functional groups. In addition, the utility of the product thus obtained was showcased by its diverse structural transformations.

Silver-catalysed double decarboxylative addition-cyclisation-elimination cascade sequence for the synthesis of quinolin-2-ones

An atom-efficient silver-catalysed double carboxylative strategy for the one-step synthesis of quinolin-2-ones via an addition-cyclisation-elimination cascade sequence of oxamic acids to acrylic acids, mediated either thermally or photochemically, is reported. The reaction was applicable to the synthesis of a broad range of quinolin-2-ones and featured a double-disconnection approach that constructed the quinolin-2-one core via the formal and direct addition of a C(sp²)-H/C(sp²)-H olefin moiety to a phenylformamide precursor.

Hypervalent Iodine(III)-Promoted Radical Oxidative C-H Annulation of Arylamines with α-Keto Acids

A novel catalyst-free radical oxidative C-H annulation reaction of arylamines with α-keto acids toward benzoxazin-2-ones synthesis under mild conditions was developed. This hypervalent iodine(III)-promoted process eliminated the use of a metal catalyst or additive with high levels of functional group tolerance. Hypervalent iodine(III) was both an oxidant and a radical initiator for this reaction. The synthetic utility of this method was confirmed by the synthesis of the natural product cephalandole A.

4-Aminoalkyl Quinolin-2-one Derivatives via Knorr Cyclisation of ω-Amino-β-Keto Anilides

In a high-yielding and solvent-free procedure N-ethoxycarbonyl protected ω-amino-β-keto anilides undergo Knorr cyclisation in neat polyphosphoric acid to provide straightforward route to 4-aminoalkyl quinolin-2-one derivatives with variable length of the alkyl chain.

Ring expansion and ring opening of 3-halooxindoles with N-alkoxycarbonyl-O-tosylhydroxylamines for divergent access to 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas

The reaction of N-alkoxycarbonyl-O-tosylhydroxylamines with indol-2-ones in situ generated from 3-halooxindoles has been developed for divergently accessing 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas in good to excellent yields.

Silver-Catalyzed Decarboxylative Radical Addition/Cyclization of Oxamic Acids with Alkenes towards Quinolin-2-ones

An efficient silver-catalyzed tandem decarboxylative radical addition/cyclization of oxamic acids with alkenes has been developed. This method provides a novel and straightforward protocol toward a variety of 4-aryl-3,4-dihydroquinolin-2(1H)-ones, 4-(α-carbonyl)-3,4-dihydroquinolin-2(1H)-ones, and quinolin-2(1H)-ones in aqueous solution.

Construction of trisubstituted chromone skeletons carrying electron-withdrawing groups via PhIO-mediated dehydrogenation and its application to the synthesis of frutinone A

The construction of the biologically interesting chromone skeleton was realized by PhIO-mediated dehydrogenation of chromanones under mild conditions. Interestingly, this method also found application in the synthesis of the naturally occurring frutinone A.

Transition-metal free direct C–H functionalization of quinoxalin-2(1H)-ones with oxamic acids leading to 3-carbamoyl quinoxalin-2(1H)-ones

A practical transition-metal free decarboxylative coupling reaction of oxamic acids with quinoxalin-2(1H)-ones has been developed under mild conditions.

A cascade approach to 3D cyclic carbamates via an ionic decarboxylative functionalization of olefinic oxamic acids

An m-CPBA-mediated intramolecular epoxidation-decarboxylative alkoxylation cascade reaction of olefinic oxamic acids has been developed.