Reductive Rearrangement of Tetraphenyldiphosphine Disulfide To Trigger the Bisthiophosphinylation of Alkenes and Alkynes

Rhodium(I) Complexes with a η1-Fluorenyl-P-phosphanylphosphorane Ligand

The first example of a P-phosphanylphosphorane, Flu═PCy2-PCy2 (L2; Flu = 9-fluorenyl), has been easily prepared by P-phosphination of lithiated 9-dicyclohexylphosphinofluorene (FluPCy2, L0) with chlorodicyclohexylphosphane. L2 constitutes a new type of P(III)-P(V) organophosphorus compound, a σ3λ3-σ4λ5 species that is stable under an inert atmosphere in the solid state. The reaction of L2 with [Rh(diene)2]BR4 causes metalation of the benzylic carbon (C9) of fluorene, giving κ2-C,P complexes in which fluorene is coordinated in the η1 form. A complex with the weakly coordinating BArF anion has been isolated and fully characterized, including its crystal structure obtained by X-ray diffraction.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Dithiophosphinylation of Allenyl Acetates: Access to 1,2-Bis(diphenylphosphino)ethane-Type Bidentate Ligands

1,2-Bis(diphenylphosphino)ethanes (DPPEs) are versatile and immensely important ligands in transition metal catalysts. Here we report the dithiophosphinylation of readily available allenyl acetates to give DPPEs in high yields and regioselectivity. This protocol features a broad substrate scope and mild conditions, avoiding the use of transition metals and air-sensitive sources of phosphorus. Mechanism studies indicate that the reaction was accomplished via an SN2'-type addition-elimination followed by a 1,4-addition step.

Regioselective One-Pot Synthesis of Vicinal Bisphosphine Derivatives from Nitroalkenes by Hydrophosphinylation/Elimination/Hydrophosphinylation

Herein, a facile method is developed for the synthesis of vicinal bisphosphine derivatives based on a cascade of hydrophosphinylation, elimination, and hydrophosphinylation of secondary phosphine oxides with nitroalkenes. This cascade reaction provides step-economy access to a series of vicinal bisphosphine derivatives with high to excellent yields (up to 99%). This method was further extended to prepare, in one-pot, regioselective vicinal bisphosphine derivatives that incorporated two different phosphorus functional groups.

Phosphino-Phosphination Reactions: Frustrated Lewis Pair Reactivity of Phosphino-Phosphonium Cations with Alkynes

The phosphino-phosphonium cations of the form [R3 PPR'2 ]+ are labile and provide access to the constituent Lewis acidic and Lewis basic fragments. This permits frustrated Lewis pair-type addition reactions to alkynes, affording unprecedented phosphino-phosphination reactions and giving cations of the form [cis-R3 PCHC(R'')PR'2 ]+ . This reactivity is further adapted to prepare several examples of a rare class of dissymmetric cis-olefin-linked bidentate phosphines.

Understanding Reactive Sulfur Species through P/S Synergy

We investigated the differential oxidative and nucleophilic chemistry of reactive sulfur and oxygen anions (SSNO-, SNO-, NO2-, S42-, and HS-) using the simple reducing electrophile PPh2Cl. In the case of SSNO- reacting with PPh2Cl, a complex mixture of mono and diphosphorus products is formed exclusively in the P(V) oxidation state. We found that the phosphine stoichiometry dictates selectivity for oxidation to P=S/P=O products or transformation to P2 species. Interestingly, only chalcogen atoms are incorporated into the phosphorus products and, instead, nitrogen is released in the form of NO gas. Finally, we demonstrate that more reducing anions (S42- and HS-) also react with PPh2Cl with P=S bond formation as a key reaction driving force.

Photoinduced Synthesis of Bisphosphinated Quinoxalines via Radical Cyclization of o-Diisocyanoarenes with Diphosphines

The cycloaddition reaction of o-diisocyanoarenes with interelement compounds under light is a very important reaction system to clarify whether this reaction proceeds by radical cyclization or by aza-Bergman cyclization. In this study, a series of diphosphines with phosphorus-phosphorus single bonds were selected as interelement compounds, and their cycloaddition reactions with o-diisocyanoarenes under light were investigated in detail to achieve a novel photoinduced synthesis of bisphosphinated quinoxalines via the radical cyclization pathway. In addition, the photoinduced reaction of diphosphines with isocyanides having o-functional groups such as cyano and ethenyl groups allowed us to elucidate the reaction pathway and product selectivity of this bisphosphination. Furthermore, the one-pot synthesis of Pd^II -quinoxaline complex was successfully achieved by applying the developed reaction.

Metal-Free One-Pot Multi-Functionalization of Unsaturated Compounds with Interelement Compounds by Radical Process

In recent years, the importance of "environmentally friendly manufacturing" has been increasing toward the establishment of a resource-recycling society. In organic synthesis, as well, it is becoming increasingly important to develop new synthetic strategies with resource conservation and the recycling of elemental resources in mind, rather than just only synthesis. Many studies on the construction of frameworks of functional molecules using ionic reactions and transition-metal-catalyzed reactions have been reported, but most of them have focused on the formation of carbon-carbon bonds. However, it is essential to introduce appropriate functional groups at appropriate positions in molecules in order for the molecules to express their functions, and furthermore, the highly selective preparation of multiple functional groups is considered important for the creation of new functional molecules. In this review, we focus on radical reactions with high functional group selectivity and overview the recent progress in practical methods for the simultaneous introduction of multiple functional groups and propose future synthetic strategies that emphasize the recycling of elemental resources and environmental friendliness.

Copper-Catalyzed Stereoselective Radical Phosphono-hydrazonation of Alkynes

A copper-catalyzed stereoselective phosphono-hydrazonation of terminal alkynes with alkyl carbazates and diarylphosphine oxides is described. This methodology provides facile access to a variety of β-hydrazonophosphine oxides in satisfactory yields. The reaction proceeds under mild conditions and exhibits good functional group tolerance. A mechanism featuring persulfate-mediated oxidative generation of phosphinoyl radicals and copper-assisted hydrazonation is proposed.

Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization

The addition of interelement compounds with heteroatom-heteroatom single bonds to carbon-carbon unsaturated bonds under light irradiation is believed to be an atomically efficient method to procure materials with carbon-heteroatom bonds. In this study, we achieved the photoinduced bisphosphination of alkynes using the phosphorus interelement compound, tetraphenyldiphosphine monosulfide (1), to stereoselectively obtain the corresponding (E)-vic-1,2-bisphosphinoalkenes, which are important transition-metal ligands. The bisphosphination reaction was performed by mixing 1 and various alkynes and then exposing the mixture to light irradiation. Optimization of the conditions for the bisphosphination reaction resulted in a wide substrate range and excellent trans-selectivity. Moreover, the completely regioselective introduction of pentavalent and trivalent phosphorus groups to the terminal and internal positions of the alkynes, respectively, was achieved. We also found that the novel double-bond isomerization reaction of the synthesized bisphosphinated products occurred with a catalytic amount of a base under mild conditions. Our method for the photoinduced bisphosphination of carbon-carbon unsaturated compounds may have strong implications for both organic synthesis and organometallic and catalyst chemistry.

Copper-Catalyzed Vicinal Cyano-, Thiocyano-, and Chlorophosphorylation of Alkynes: A Phosphinoyl Radical-Initiated Approach for Difunctionalized Alkenes

A copper-catalyzed difunctional cyano-, thiocyano-, and chlorophosphorylation reaction of alkynes with P(O)-H compounds and coupling partners (TBACN, TMSNCS, TMSCl) is described. The reaction introduces versatile groups (-P(O)R₂ and -CN, -SCN, or -Cl) to form tri- and tetrasubstituted alkenyl phosphine oxides/phosphonates regio- and stereoselectively.

Highly regio- and stereoselective phosphinylphosphination of terminal alkynes with tetraphenyldiphosphine monoxide under radical conditions

The homolytic cleavage of the P^V(O)–P^III bond in tetraphenyldiphosphine monoxide simultaneously provides both pentavalent and trivalent phosphorus-centered radicals with different reactivities. The method using V-40 as an initiator is successfully investigated for the regio- and stereoselective phosphinylphosphination of terminal alkynes giving the corresponding trans-isomers of 1-diphenylphosphinyl-2-diphenylthiophosphinyl-1-alkenes in good yields. The protocol can be applied to a wide variety of terminal alkynes including both alkyl- and arylalkynes.

Photoinduced Syntheses and Reactivities of Phosphorus-Containing Interelement Compounds

The photoinduced reactions of tetraphenyldiphosphine disulfide with a range of organic dichalcogenides successfully afforded a series of phosphorus(V)-chalcogen interelement compounds via a radical process. The relative reactivities of the organic dichalcogenides (i.e., (PhS)₂, (PhSe)₂, and (PhTe)₂) toward the P^III or P^V groups in the diphosphine analogues under light were investigated in detail, and a convenient method was developed to form P-S or P-Se interelement compounds from tetraphenyldiphosphine disulfide and (PhS)₂ or (PhSe)₂ upon photoirradiation. Furthermore, the relative photochemical properties and reactivities of tetraphenyldiphophine (P-P interelement compound) and its analogues toward photoinduced radical addition reactions were also discussed. The formed P-E (E = S, Se) interelement compounds could be utilized for ionic reactions, and they could be transformed into various phosphine reagents via one-pot processes.

1,1-Addition of α-C2-Bridged Biphospholes with Alkynes

An unusual chemoselective 1,1-addition of α-C₂-bridged biphospholes to terminal alkynes is reported. The developed protocol provides simple access to the unknown 1,3-diphosphepines, which has potential applications in the coordination and catalyst chemistry. Their Pd and Mo complexes were studied by single-crystal X-ray diffraction analysis. This method features excellent chemoselectivity, high step and atom economy, mild reaction conditions, and wide substrate scope.

Synthesis of DPPP- and DPPPEN-Type Bidentate Ligands by Ring-Opening Diphosphination of Methylene- and Vinylcyclopropanes under Visible-Light-Promoted Photoredox Catalysis

A ring-opening diphosphination of methylene- and vinylcyclopropanes with tetraaryldiphosphines (Ar₂P-PAr₂) has been developed to afford the corresponding 1,3-diphenylphosphinopropane- and 1,3-diphenylphosphinopentane-type bidentate ligands, respectively. The reaction proceeds under bromine cation-initiated, visible-light-promoted photoredox catalysis at ambient temperature. Owing to the ready availability of functionalized diphosphines, the electronically diverse MeO- and CF₃-substituted bidentate ligands are also easily prepared.