Visible-Light-Driven Selective Alkenyl C–P Bond Cleavage of Allenylphosphine Oxides

Efficient C(sp3)-P(V) bond cleavage and reconstruction of free α-aminophosphonates via palladium catalysis

Transition metal-catalyzed cleavage and reconstruction of the C-P bond provides a highly efficient and rapid method for the transformation of organophosphine compounds. In this study, a novel and general protocol for the palladium-catalyzed C(sp3)-P(V) bond cleavage of free α-aminophosphonates and subsequent functionalization via C-P bond recombination has been developed. The reaction exhibits high reactivity between the C(sp3)-P bond and halides, accommodating a wide range of substrates and enabling the rapid synthesis of aryl, alkenyl, and alkyl organophosphine molecules. Additionally, the synthetic utility is validated by gram-scale synthesis, and the reaction process is corroborated by mechanistic experiments.

Electrochemically Enabled Hydroxyphosphorylation of 1,3-Enynes to Access Phosphinyl-Substituted Propargyl Alcohols

Catalytic difunctionalization with the direct activation of (O)P-H bonds has been recently established as a potentially robust platform to generate valuable organophosphorus compounds. In terms of 1,3-enynes, despite of the various catalytic methods developed for hydrophosphorylation, the radical-mediated hetero-functionalization of two different atoms has been less explored. In this study, we disclosed an electrochemically induced hydroxyphosphorylation of 1,3-enynes for the construction of phosphinyl-substituted propargyl alcohols. The system involves the direct activation of both arylphosphine oxides and oxygen in ambient air with no external metal or additive needed. The use of electrochemistry ensures the regioselective, atom-economic and eco-friendly for the difunctionalization process. This strategy highlights the advantages of mild reaction conditions, readily available starting materials and broad substrate scope, showing its practical synthetic value in organic synthesis.

Access Polyarylbipyrazoles via Palladium-Catalysis and Visible-Light-Driven C(sp3)-P(V) Cleavage Relay Strategy

An unprecedented palladium-catalyzed and visible-light-driven relay reaction of allenylphosphine oxide with in situ generated nitrile imines is presented for the direct synthesis of highly valuable polyarylbipyrazole skeletons. This one-pot strategy involves double 1,3-dipolar cycloaddition and C(sp3)-P(V) bond cleavage under photocatalyst-free and mild reaction conditions. The approach features simple operation, a high step economy, and a broad substrate scope, affording the corresponding products in moderate to excellent yields.

Tandem SN2 Nucleophilic Substitution/Phospho-Dieckmann Reaction: One-Step Synthesis of 2-Phosphonyl-3-hydroxybenzo[b]thiophenes

A novel and efficient tandem SN2 nucleophilic substitution/Dieckmann condensation reaction of α-iodomethyl phosphine oxide with methyl thiosalicylate derivatives has been developed by using NaOH as a base, which enables the expeditious synthesis of 2-phosphonyl-3-hydroxybenzo[b]thiophene derivatives in moderate to high yields under simple conditions. This research provides not only a convenient method for the functionalization of benzo[b]thiophenes at the 2-position and 3-position but also new organophosphorus molecules. Furthermore, several new phosphonyl-substituted benzo[b]thiophenes were obtained from the resultant 2-phosphonyl-3-hydroxybenzo[b]thiophenes.

Mn(iii)-mediated C-P bond activation of diphosphines: toward a highly emissive phosphahelicene cation scaffold and modulated circularly polarized luminescence

Transition metal mediated C-X (X = H, halogen) bond activation provides an impressive protocol for building polyaromatic hydrocarbons (PAHs) in C-C bond coupling and annulation; however, mimicking both the reaction model and Lewis acid mediator simultaneously in a hetero-PAH system for selective C-P bond cleavage faces unsolved challenges. At present, developing the C-P bond activation protocol of the phosphonic backbone using noble-metal complexes is a predominant passway for the construction of phosphine catalysts and P-center redox-dependent photoelectric semiconductors, but non-noble metal triggered methods are still elusive. Herein, we report Mn(iii)-mediated C-P bond activation and intramolecular cyclization of diphosphines by a redox-directed radical phosphonium process, generating phosphahelicene cations or phosphoniums with nice regioselectivity and substrate universality under mild conditions. Experiments and theoretical calculations revealed the existence of the unusual radical mechanism and electron-deficient character of novel phosphahelicenes. These rigid quaternary bonding skeletons facilitated versatile fluorescence with good tunability and excellent efficiency. Moreover, the enantiomerically enriched crystals of phosphahelicenes emitted intense circularly polarized luminescence (CPL). Notably, the modulated CPL of racemic phosphahelicenes was induced by chiral transmission in the cholesteric mesophase, showing ultrahigh asymmetry factors of CPL (+0.51, -0.48). Our findings provide a new approach for the design of emissive phosphahelicenes towards chiral emitters and synthesized precursors.

Visible-Light-Induced Palladium-Catalyzed Construction of Polyarylfuran Skeletons via Cascade Aryl Radical Cyclization and C(sp3)-P(V) Bond Cleavage

Herein, a novel and expedient method was established for the synthesis of polyarylfuran derivatives. The coupling of allenylphosphine oxide and bromophenol or bromonaphthol enabled by visible light and palladium catalysis directly furnishes polyarylfuran skeletons, which involves a radical tandem cyclization and cascade C(sp³)-P(V) bond cleavage. This protocol features easy operation, a broad substrate scope, and a high step economy, affording polyarylfurans in moderate to good yields.

Substituents Regulate the Cyclization of Conjugated Alkynes to Accurately Construct Cyclo-(E)-[3]dendralenes

Substituent-regulated cyclization of conjugated alkynes with acid catalysis was developed in this paper, and it provides a straightforward synthesis of cyclic-(E)-[3]dendralenes. Depending on the electronic effect of the aromatic ring pairing, a variety of phosphinyl quintuplet/hexa cyclo-[3]dendralenes with diverse substitution patterns are accessible, with good efficiency and high stereoselectivity. This self-cyclization process achieves the first precise construction of a phosphinylcyclo-(E)-[3]dendralene from conjugated alkynes to aromatization.

Electro-Triggered Cascade Cyclization to Access Phosphinyl-Substituted N-Containing Heterocycles

An electro-triggered cascade cyclization strategy was disclosed with concomitant phosphinylation and N-heterocycle construction. It provides a novel and environmentally friendly approach to access phosphinyl-substituted N-heterocycles with no external metal catalyst, oxidant, or heating. Mechanistic studies have revealed that anodic oxidation of H-phosphorus compounds occurs first to generate the key P-centered radical directly and cathodic reduction leads to the concurrent release of molecular hydrogen or methane. This protocol features simple operation, broad substrate scope, clean and mild conditions, and atom and step economy to form heterocycle-containing organophosphorus scaffolds.

Radical modulated regioselective difunctionalization of vinyl enynes: tunable access to naphthalen-1(2H)-ones and allenic alcohols

A novel and efficient radical-modulated difunctionalization of vinyl enynes has been disclosed using TEMPO as a radical regulator. Facile access to structurally diverse 3-bromo-naphthalen-1(2H)-ones and 4-bromo-allenic alcohols was realized via 1,2-addition/1,2-migration or 1,4-addition, respectively. This protocol represents the first example of radical-modulated metal-free difunctionalization of 1,3-enynes with high regioselectivity.

Metal-free C(aryl)–P bond cleavage: Experimental and computational studies of the Michael addition/aryl migration of triarylphosphines to alkenyl esters

The nucleophilic addition and aryl migration of triarylphosphines to alkynyl esters in the presence of water results in the formation of 3-(diarylphosphoryl)-3-aryl propanoic acid derivatives through a metal-free C(aryl)–P bond...

Visible-light-facilitated P-center radical addition to C[double bond, length as m-dash]X (X = C, N) bonds results in cyclizations

Visible-light-facilitated phosphorus radical reactions have been developed as a powerful and sustainable tool for the synthesis of various organophosphorus compounds. In general, these reactions require stoichiometric amounts of oxidants, and reductants, bases, and radical initiators, leading to uneconomical and complicated processes. Progress has been made over the past few years toward using reactions that proceed under eco-benign and mild reaction conditions. Furthermore, these reactions have broad functional group tolerance, with some facile and economical pathways. Herein, we summarize the discoveries and achievements pertaining to C-P bond formation through a visible light photocatalysis procedure with high atom economy, made by our group and other research groups. It was established that greener and more environmentally friendly approaches do not require an additional oxidant or base. Moreover, we have designed and synthesized a new type of P-radical precursor, which can take part in reactions without the requirement for any additional bases, oxidants, and additives. This breakthrough, pertaining to novel visible-light-induced transformations, will be discussed and a plausible mechanism is proposed, based on corresponding experiments and the literature.

Visible-Light-Induced 1,4-Hydroxysulfonylation of Vinyl Enynes with Sulfonyl Chlorides: The Bridge of Chloride Linking Water and Enynes

A novel visible-light-induced 1,4-hydroxysulfonylation of vinyl enynes with sulfonyl chlorides has been established, providing a highly efficient protocol to access multisubstituted sulfonyl allenic alcohols. Control experiments and mechanistic studies disclose that the target products result from sequential reactions of hydroxyl and tosyl radicals, among which chloride anion plays a key role to generate the requisite ^•OH, thus bridging water and enynes. Moreover, the vinyl pendant is believed to decisively affect the site-selectivity of hydroxyl radical.

Visible light mediated functionalization of allenes

This review summarizes the visible light mediated strategies for the functionalization of allenes.

Photocatalytic transition-metal-free direct 3-alkylation of 2-aryl-2H-indazoles in dimethyl carbonate

A general transition-metal-free photocatalytic decarboxylative 3-alkylation reaction of 2-aryl-2H-indazoles was developed under visible-light irradiation under mild conditions.

Visible-Light-Induced Phosphorylation of Imidazo-Fused Heterocycles under Metal-Free Conditions

A metal-free and base-free procedure for the phosphorylation of imidazo[1,2-a]pyridines with phosphine oxides under the irradiation of visible light at room temperature in green solvent was reported, featuring mild and sustainable conditions, convenient operation, as well as good functional group compatibility.