Alkoxycarbonyl Radicals Research Articles

Visible light-promoted C3-H alkoxycarbonylation of quinoxalin-2(1H)-ones or coumarins with alkyloxalyl chlorides.

Herein, we describe a green and efficient photoredox catalytic C3-H alkoxycarbonylation between quinoxalin-2(1H)-ones or coumarins and readily available alkyloxalyl chlorides under ambient conditions. A series of quinoxaline-3-carbonyl and coumarin-3-carbonyl compounds are prepared through the radical addition of in situ-generated alkoxycarbonyl radicals. Notably, this protocol features mild conditions, operational simplicity, and excellent functional group tolerance. More importantly, the carboxylated products can be readily derivatized into other important compounds that would be of great potential for the exploitation of pharmaceutically active compounds.

Alkoxycarbonylation-triggered nitrile insertion/remote C(sp2)–H and C(sp3)–H functionalization to access esterified quinazolinones and amidines

A new alkoxycarbonyl radical triggered nitrile insertion/remote C(sp2)–H and C(sp3)–H functionalization reaction is developed.

Synthesis of Isoquinolinediones via the Radical Addition/Cyclization of N‐Alkyl‐N‐methacryloylbenzamides with Monoalkyl Oxalates

AbstractA photocatalytic reaction of N‐alkyl‐N‐methacryloylbenzamides with monoalkyl oxalates is described. Monoalkyl oxalates undergo single‐electron oxidation/CO2 extrusion to generate alkoxycarbonyl radicals, followed by the addition and subsequent cyclization to give alkoxycarbonyl substituted isoquinolinediones. A wide variety of monoalkyl oxalates were amenable in this protocol, affording various alkoxycarbonyl substituted isoquinolinediones.

Synthesis of N-Phenylcarbamate by C–N Coupling Reaction without Metal Participation

AbstractWe have developed a new method for the synthesis of carbamates from amine and hydrazine formate. The reaction occurs in the presence of iodine and tert-butyl hydroperoxide, in which carbazates are produced via alkoxycarbonyl radical formation for cross-coupling reaction. The method exhibits broad functional group tolerance and affords a series of N-phenylcarbamates in moderate to good yields. Remarkably, our approach is metal free and utilizes cheap, readily available raw materials and relatively universal substrates.

Visible-Light-Induced 1,7-Enyne Dicyclization: Synthesis of Ester-Substituted Benzo[j]phenanthridines.

A novel alkoxycarbonyl-radical-triggered cascade cyclization of 1,7-enynes, with alkyloxalyl chlorides as the ester units, for the synthesis of benzo[j]phenanthridines is described. The reaction conditions exhibit excellent compatibility with a broad range of alkoxycarbonyl radical sources and realize the installation of an ester group in the polycyclic compound. This radical cascade cyclization reaction features excellent functional group tolerance, mild reaction conditions, and good to excellent yields.

Synthesis of Ester-Containing Chroman-4-Ones via Cascade Radical Annulation of 2-(Allyloxy)Arylaldehydes with Oxalates under Metal Free Conditions.

A convenient and practical method for the synthesis of bioactive ester-containing chroman-4-ones through the cascade radical cyclization of 2-(allyloxy)arylaldehydes and oxalates is described. The preliminary studies suggest that an alkoxycarbonyl radical might be involved in the current transformation, which was generated via the decarboxylation of oxalates in the presence of (NH4)2S2O8.

Electrochemical Fe-catalysed radical cyclization for the synthesis of oxindoles.

We report an efficient and sustainable electrocatalytic approach for the synthesis of 3,3-disubstituted 2-oxindoles bearing ester groups from readily accessible N-arylacrylamides and carbazates. The reaction proceeds through an electrochemical iron-catalyzed radical addition/cyclization sequence with a commercially available iron catalyst and carbazates as alkoxycarbonyl radical precursors. This mild and operationally simple method transforms a wide range of structurally diverse N-arylacrylamides into oxindole derivatives in good yields and can be smoothly scaled up for the preparation of synthetically valuable oxindoles that are key intermediates for the synthesis of natural products.

Electrochemical Metal‐Catalyzed Azidoesterification of Alkenes

AbstractWe report an efficient and sustainable electrocatalytic approach for azidoesterification of alkenes. The reaction proceeds by electrochemical iron‐catalyzed oxidation of commercially available carbazates to produce alkoxycarbonyl radicals. Upon addition across alkenes, the generated transient carbon‐centered radicals get trapped by azido metal complexes to furnish the alkene difunctionalization products. This mild, operationally simple protocol transforms a wide variety of alkenes into the corresponding β‐azido esters in good to excellent yields, thereby providing a practical access to β‐amino acid derivatives from simple and readily available starting materials.

Pairing Iron and Nickel Catalysis for Electrochemical Esterification of Aryl Halides with Carbazates.

We report an electrocatalytic approach for esterification of aryl halides by pairing iron and nickel electrocatalysis. The reaction involves anodically iron-catalyzed oxidation of carbazates to produce alkoxycarbonyl radicals. The carbon-centered radicals then enter nickel catalysis that is powered by cathodic reduction to deliver the radical coupling products. Mechanistic data are consistent with arylnickel(II) species as the key intermediates enabling the desired carbon-carbon bond formation.

Photoredox-Catalyzed Allylic Defluorinative Alkoxycarbonylation of Trifluoromethyl Alkenes through Intermolecular Alkoxycarbonyl Radical Addition.

The gem-difluoroalkene moiety is an ideal carbonyl bioisostere in medicinal chemistry, but efficient synthesis of β-gem-difluoroalkene esters remains challenging so far. Herein, we disclose a photoredox-catalyzed allylic defluorinative alkoxycarbonylation of trifluoromethyl alkenes enabled by intermolecular alkoxycarbonyl radical addition. A wide variety of alcohol oxalate derivatives were amenable, affording various β-gem-difluoroalkene esters with excellent functional group tolerance. Notably, the potential synthetic value of this method is highlighted by successful late-stage modification for bioactive molecules.

Efficient access to aliphatic esters by photocatalyzed alkoxycarbonylation of alkenes with alkyloxalyl chlorides

Aliphatic esters are essential constituents of biologically active compounds and versatile chemical intermediates for the synthesis of drugs. However, their preparation from readily available olefins remains challenging. Here, we report a strategy to access aliphatic esters from olefins through a photocatalyzed alkoxycarbonylation reaction. Alkyloxalyl chlorides, generated in situ from the corresponding alcohols and oxalyl chloride, are engaged as alkoxycarbonyl radical fragments under photoredox catalysis. This transformation tolerates a broad scope of electron-rich and electron-deficient olefins and provides the corresponding β-chloro esters in good yields. Additionally, a formal β-selective alkene alkoxycarbonylation is developed. Moreover, a variety of oxindole-3-acetates and furoindolines are prepared in good to excellent yields. A more concise formal synthesis of (±)-physovenine is accomplished as well. With these strategies, a wide range of natural-product-derived olefins and alkyloxalyl chlorides are also successfully employed.

Photoredox Ni-Catalyzed Selective Coupling of Organic Halides and Oxalates to Esters via Alkoxycarbonyl Radical Intermediates

A new approach for radical cross coupling of organic halides and oxalates toward esters has been developed via photoredox nickel dual catalysis. This method has been demonstrated for transformation...

Copper-Catalyzed Coupling of Amines with Carbazates: An Approach to Carbamates.

A new approach for the preparation of carbamates via the copper-catalyzed cross-coupling reaction of amines with alkoxycarbonyl radicals generated from carbazates is described. This environmentally friendly protocol takes place under mild conditions and is compatible with a wide range of amines, including aromatic/aliphatic and primary/secondary substrates.

Photocatalytic acyl azolium-promoted alkoxycarbonylation of trifluoroborates

Despite recent advancements in the selective generation and coupling of organic radical species, the alkoxycarbonyl radical remains underexplored relative to other carbon-containing radical species. Drawing inspiration from new strategies for generating acyl radical equivalents utilizing dual N-heterocyclic carbene catalysis and photocatalysis, we have prepared dimethylimidazolium esters that can function as an alkoxycarbonyl radical surrogate under photocatalytic conditions. We demonstrate the synthetic utility of these azolium-based partners through the preparation of esters arising from the coupling of this radical surrogate with an oxidatively generated alkyl radical.

Photoinduced Oxidative Alkoxycarbonylation of Alkenes with Alkyl Formates

A photoinduced oxidative alkoxycarbonylation of alkenes initiated by intermolecular addition of alkoxycarbonyl radicals has been demonstrated. Employing alkyl formates as alkoxycarbonyl radical sources, a range of α,β-unsaturated esters were obtained with good regioselectivity and E selectivity under ambient conditions.

Alkoxycarbonyl radicals from alkyloxalyl chlorides: photoinduced synthesis of isoquinolinediones under visible light irradiation

Alkyloxalyl chlorides, generated from alcohols and oxalyl chlorides, are used as alkoxycarbonyl radicals in the reaction of N-acryloyl benzamides under photocatalysis at room temperature.

Iron-catalyzed radical cascade 6-endo cyclization of dienes towards fused nitrogen heterocycles initiated by an alkoxycarbonyl radical.

An iron-catalyzed radical cascade cyclization of dienes initiated by an alkoxycarbonyl radical has been developed in the presence of (NH4)2S2O8, leading to a series of fused nitrogen heterocyclic compounds under relatively mild reaction conditions. The reaction is triggered by the addition of an alkyoxycarbonyl radical derived from the cleavage of alkoxyformyl hydrazide. Afterward, the formed nucleophilic radical preferred addition to the electron-neutral vinyl rather than the electron-deficient vinyl, followed by cascade 6-endo cyclization and further radical cyclization.

Facile Preparation of Spirolactones by an Alkoxycarbonyl Radical Cyclization-Cross-Coupling Cascade.

An alkoxycarbonyl radical cyclization-cross-coupling cascade has been developed that allows functionalized γ-butyrolactones to be prepared in one step from simple tertiary alcohol-derived homoallylic oxalate precursors. The reaction succeeds with aryl and vinyl electrophiles and is compatible with heterocyclic fragments in both coupling partners. This chemistry allows for the rapid construction of spirolactones, which are of interest in drug discovery endeavors.

Facile Preparation of Spirolactones by an Alkoxycarbonyl Radical Cyclization–Cross‐Coupling Cascade

AbstractAn alkoxycarbonyl radical cyclization–cross‐coupling cascade has been developed that allows functionalized γ‐butyrolactones to be prepared in one step from simple tertiary alcohol‐derived homoallylic oxalate precursors. The reaction succeeds with aryl and vinyl electrophiles and is compatible with heterocyclic fragments in both coupling partners. This chemistry allows for the rapid construction of spirolactones, which are of interest in drug discovery endeavors.

ChemInform Abstract: Methoxycarbonyl Migration in 3‐Methylene‐1,4‐cyclohexadienes. An Extension of the von Auwers Rearrangement.

Upon heating, 3-methylene-1,4-cyclohexadienes possessing an alkoxycarbonyl substituent in position 6 undergo rearrangement and concomitant aromatization to give the corresponding arylacetates. This transformation represents a modification of the von Auwers rearrangement and proceeds by a radical chain mechanism. The intermediate alkoxycarbonyl radical can be intercepted allowing further useful synthetic variations.