Visible Light-Mediated Photocatalytic Metal-Free Cross-Coupling Reaction of Alkenyl Carboxylic Acids with Diarylphosphine Oxides Leading to β-Ketophosphine Oxides

Trivalent Phospha-Brook rearrangement enabled practical deoxygenative phosphonylation of carbonyls

Brønsted base-mediated [1,2]-phospha-Brook rearrangements have garnered considerable attention for developing new methodologies and efficiently constructing complex molecular structures. However, the strict reliance on pentavalent phosphonates imposes strong limitations on the reaction types, and the mechanistic constraint also excludes the involvement of trivalent phosphine in the same pathway. In this study, we employ Lewis acid rather than Brønsted base to shift the charge transfer from the previous O-P-C direction to a P-C-O process. This orthogonal approach can undergo the unprecedented C-O bond cleavage instead of traditional C-P bond splitting and enables the deoxygenative phosphorylation of carbonyl compounds under metal-free conditions to rapid access various tertiary phosphine oxides. The reaction demonstrates excellent substrate scope, remarkable functional group compatibility, and operational simplicity, offering significantly enhanced atom-economy compared to previous deoxygenative strategies. Additionally, detailed mechanistic studies reveal an unusual oxygen atom crossover and clearly elucidate the mechanism of this Lewis acid-mediated trivalent phospha-Brook rearrangement. These insights further deepen the understanding of trivalent phosphorus chemistry and pave the way for the design of related reactions.

Visible-Light-Induced Decarboxylative Annulation of α,β-Unsaturated Acids with Amines and α-Keto Acids for 2,4-Diarylquinoline Synthesis

An efficient and sustainable approach for the synthesis of 2,4-diarylquinolines has been developed via a visible-light-promoted metal-free three-component decarboxylative annulation pathway. This one-pot protocol combines readily available feed-stock α,β-unsaturated acids, aromatic amines, and α-keto acids in a cascade manner to access substituted quinolines under eco-benign conditions. Moreover, mechanistic insights suggest initial C-C cross coupling followed by decarboxylative 6π electrocyclic annulation to afford the desired products. The broad substrates scope and excellent functional group tolerance make this protocol more attractive and synthetically applicable toward the construction of complex N-heterocycles.

Photocatalytic Decarboxylative Cross-Coupling of α,β-Unsaturated Acids with Amines for α-Ketoamides via C-N Bond Formation

An unprecedented oxidative decarboxylative chemical domain of α,β-unsaturated acids and amines for C-N cross-coupled α-ketoamidation is disclosed. Molecular oxygen as a source oxygen in amide and water oxygen in the ketone segment furnished a green and sustainable synthesis of α-ketoamide from feedstock acids and amines. Mechanistically, photocatalyst travels with reductive quenching cycle, whereas pallado-cycle proceeded through oxidative C-N bond formation. Broad substrate scope, functional group tolerance, and CO2 and H2O as traceless byproducts make the present methodology more efficient and attractive.

Photocatalytic decarboxylation of free carboxylic acids and their functionalization

Visible light mediated decarboxylative functionalization of carboxylic acids and their derivatives has recently emerged as a novel and powerful toolkit for small molecule activation in diverse carbon-carbon and carbon-hetero bond forming reactions. Naturally abundant highly functionalized bench-stable carboxylic acid analogs have been employed as promising alternatives to non-trivial organometallic reagents for mild and eco-benign synthetic transformation with traceless CO2 by-products. In this highlight article, we focus on the development of various photodecarboxylative functionalization strategies along with intra/inter-molecular cyclization via concerted single electron transfer (SET) or energy transfer (ET) pathways. Moreover, widely explored carboxylic acids are systematically classified here into four categories; i.e., α-keto, aliphatic, α,β-unsaturated, and aromatic analogs for a concise overview to the readership. The association of decarboxylative radical species with coupling partners to construct C-C and C-N/O/S/P/X bonds for each analogous acid has been presented in brief.

Copper-Catalyzed Selective Three-Component 1,2-Phosphonoazidation of 1,3-Dienes

We report a copper-catalyzed selective 1,2-phosphonoazidation of conjugated dienes. This three-component reaction is achieved by using readily available P(O)-H compounds and bench-stable NaN3. Salient features of this strategy include its mild reaction conditions, broad functional group tolerance, and high chemoselectivity and regioselectivity. Moreover, the compatibility with the late-stage functionalization of drug molecules, the potential for scalable production, and the feasibility of further modifications of the products underscore the practical utility of this protocol in synthetic applications.

Blue-Light Driven Iron-Catalyzed Oxy-phosphinylation of Activated Alkenes for β-Ketophosphine Oxide Synthesis

We have developed an original blue-light mediated iron-catalyzed oxy-phosphinylation of activated alkenes by secondary phosphine oxides under air at room temperature. Various β-ketophosphine oxides were then obtained in 43-97 % isolated yields. Control experiments revealed that radical process is involved in the mechanism.

Copper-Catalyzed Aerobic Oxidative/Decarboxylative Phosphorylation of Aryl Acrylic Acids with P(III)-Nucleophiles

A copper-catalyzed aerobic oxidative/decarboxylative phosphorylation of aryl acrylic acids with P(III)-nucleophiles via the Michaelis-Arbuzov rearrangement for the synthesis of β-ketophosphine oxides, β-ketophosphinates, and β-ketophosphonates is reported. The present reaction could be conducted effectively without the use of a ligand and a base. Various kinds of aryl acrylic acids and P(III)-nucleophiles are tolerated in the transformation, generating the desired β-keto-organophosphorus compounds as a valuable class of phosphorus-containing intermediates with good to excellent yields. In addition, the possible mechanism and kinetic studies for the reaction have been explored by step-by-step control experiments and competitive experiments, and the results proved that this transformation may follow second-order chemical kinetics as well as involve a radical process.

Visible-Light-Induced Regioselective Radical Oxo-Amination of Alkenes with O2 as the Oxygen Source

An efficient and novel visible-light-induced oxo-amination of terminal alkenes for the construction of α-amino ketones with easily accessible and green O2 as the oxygen source has been developed. The transformation possesses the advantages of operational simplicity, a broad substrate scope, high atom economy, and mild reaction conditions. The mechanistic studies reveal that an energy transfer process probably occurs in the initial stage, and the reaction proceeds via β-scission of the alkoxyl radical species.

NIS-initiated photo-induced oxidative decarboxylative sulfoximidation of cinnamic acids

N-Iodosuccinimide catalyzed, visible-light-induced oxidative decarboxylative cross-coupling between cinnamic acids and NH-sulfoximines is presented. This strategy results in the formation of α-keto-N-acyl sulfoximines via the construction of two new CO bonds and one C-N bond. The in situ-generated N-iodosulfoximine serves as the light-absorbing species in the absence of any external photosensitizer. The keto carbonyl and amidic carbonyl oxygen in the resulting product originate from dioxygen and water respectively.

Nickel-Catalyzed Radical Ring-Opening Phosphorylation of Cycloalkyl Hydroperoxides Leading to Distal Acylphosphine Oxides

A facile and efficient nickel-catalyzed C-C bond cleavage/phosphorylation of various cycloalkyl hydroperoxides was developed. This radical ring-opening strategy provided practical access to structurally diverse distal ketophosphine oxides in one pot through concurrent C═O/C-P bond formation with high atom economy under mild room temperature and base-free conditions.

Copper-Catalyzed Radical Hydrazono-Phosphorylation of Alkenes

An efficient copper-catalyzed radical hydrazono-phosphorylation of alkenes with hydrazine derivatives and diarylphosphine oxides is described. The reaction provides a general and convenient method toward the synthesis of diverse β-hydrazonophosphine oxides in satisfactory yields. Based on conducted mechanistic experiments, a mechanism involving Ag-catalyzed oxidative generation of phosphinoyl radicals and subsequent addition to alkenes followed by Cu-assisted hydrazonation is proposed. Moreover, the practicability of the reaction is successfully demonstrated by its successful application on a gram scale.

Copper-Catalyzed Cross-Coupling of Alkyl and Phosphorus Radicals for C(sp3)-P Bond Formation

A Cu^I-catalyzed cross-coupling of alkyl- and phosphorus-centered radicals for C(sp³)-P bond formation is introduced. Diacyl peroxides, generated in situ from aliphatic acids and H₂O₂, serve as a source for alkyl radicals and also an initiator for the generation of phosphorus radicals from H-P(O) compounds.

Visible-light-mediated tandem phosphorylation/cyclization for the synthesis of phosphorylated oxindoles

The visible-light-mediated tandem phosphorylation/cyclization of N-arylacrylamides with H-phosphine oxides has been developed for the synthesis of phosphorylated oxindoles. This efficient and facile process was useful for the construction of a C-P bond and triggered the formation of a C-C bond with good compatibility with functional groups undermild reaction conditions.

Copper-catalyzed oxidative phosphonoheteroarylation of alkenes with phosphonates and N-heteroarenes via P–H/C–H functionalization

Copper-catalyzed oxidative phosphonoheteroarylation of alkenes with phosphonates and nucleophilic N-heteroarenes via P–H/C–H functionalization is depicted.

Excited-state cobaloxime catalysis enabled scalable oxidant-free dehydrogenative C–H phosphinoylation of undirected heterocycles

Visible-light-induced excited-state cobalt catalysis enables C(sp2)–H/C(sp3)–H phosphinoylation accompanied by H2 evolution. The reaction achieves the late-stage modification of more than 10 distinct classes of heterocycles and arenes.

Silver-Catalyzed Radical Ring-Opening of Cycloalkanols for the Synthesis of distal acylphosphine oxides

A novel silver-catalyzed ring-opening approach for the regioselective synthesis of distal acylphosphine oxides is described. A variety of distal acylphosphine oxides were prepared from the reaction of tertiary cycloalkanols (4...

Visible Light-Driven and Singlet Oxygen-Mediated Photochemical Cross-Dehydrogenative C3-H Sulfenylation of 4-Hydroxycoumarins with Thiols Using Rose Bengal as a Photosensitizer

A visible light (white light-emitting diode/direct sunlight)-driven photochemical synthesis of a new series of biologically interesting 3-(alkyl/benzylthio)-4-hydroxy-2H-chromen-2-ones has been achieved through a cross-dehydrogenative C₃-H sulfenylation of 4-hydroxycoumarins with thiols at ambient temperature in the presence of rose bengal in acetonitrile under an oxygen atmosphere. The notable features of this newly developed method are mild reaction conditions, energy efficiency, metal-free synthesis, good to excellent yields, use of low-cost materials, and eco-friendliness.

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.

Visible light-induced aerobic dioxygenation of α,β-unsaturated amides/alkenes toward selective synthesis of β-oxy alcohols using rose bengal as a photosensitizer

The first visible light-induced aerobic dioxygenation of alkenes for the selective synthesis of β-oxy alcohols was developed using non-toxic rose bengal as a photosensitizer.

Manganese(iii)-promoted tandem phosphinoylation/cyclization of 2-arylindoles/2-arylbenzimidazoles with disubstituted phosphine oxides

A simple and practical method for the synthesis of phosphoryl-substituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinolin-6(5H)-ones through manganese(iii)-promoted tandem phosphinoylation/cyclization of 2-arylindoles or 2-arylbenzimidazoles with disubstituted phosphine oxides was developed. In this transformation, new C-P bond and C-C bond were constructed simultaneously under silver-free conditions, exhibiting a broad substrate scope. It was noted that not only diarylphosphine oxides but also dialkyl and arylalkyl-phosphine oxides were compatible with the conditions.

Recent applications of Rose Bengal catalysis in N-heterocycles: a short review

The visible light harnessing ability of Rose Bengal, an organic dye, has been extensively employed in organic chemistry over the last few years. In visible light mediated reactions, this photoredox catalyst operates through multiple pathways and has the ability to provide distinctly different and valuable results. The most significant of these results are bond creation, bond functionalization, particularly for C–H and C–heteroatom bonds, and cross couplings. It is crucial to study these cases whenever these bond formations and couplings lead to the formation of heterocyclic compounds or their functionalization. The diverse biological activity and medicinal applications of heterocyclic compounds is an extensively explored area. This review primarily attempts to demonstrate the synthetic potential of Rose Bengal for synthesis and site selective functionalization of nitrogen containing heterocycles.

The recent applications of Rose Bengal as a photocatalyst for the synthesis and functionalization of N-heterocycles have been discussed.

Visible-light-driven metal-free aerobic synthesis of highly diastereoselective phosphinoylpyrroloindoles

A tandem C–P and C–C bond formation promoted by visible light at room temperature in a highly diastereoselective manner is described.

Visible light-mediated CP bond formation reactions

Organophosphorus compounds have attracted continuous attention in materials science, agrochemical and pharmaceutical fields due to their unique bioactivities. Thus, the development of novel and robust manners for the construction new CP bond has therefore gained great interests in synthetic organic chemistry. Because of their intrinsic sustainability and green chemistry character, visible light-induced photoredox catalysis has been widely applied in the construction of new chemical bonds, including the formation of CP bond. In this review, we summarized recent achievements in CP bond formation reactions initiated by visible light-induced photoredox catalysis, which mainly focusing on the discussion of reaction design and the mechanism.

An efficient preparation of β-ketophosphine oxides from alkynylphosphine oxides with benzaldehyde oxime as a hydroxide source

An effective transition-metal-free method has been developed for the preparation of β-ketophosphine oxides from alkynylphosphine oxides with benzaldehyde oxime.

Recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis

This review highlights the recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis.