P-stereogenic Phosphines Research Articles

N-Heterocyclic Carbene Enabled Copper Catalyzed Asymmetric Synthesis of Pyrimidinyl Phosphine with both Axial and P-Stereogenicity.

P-stereogenic phosphines, renowned for their utility as ligands and catalysts, have been instrumental in the field of asymmetric catalysis. However, the catalytic asymmetric synthesis of chiral ligands possessing both axial and phosphine chirality remains a significant challenge. Here, we present the successful demonstration of a Cu-catalyzed asymmetric C-P construction using in situ generated secondary phosphine and heteroaryl chloride. By introducing a chiral NHC ligand and an achiral diphosphine auxiliary ligand, we effectively alleviated the poisoning effect caused by phosphine(III) compounds and suppressed the nonenantioselective background reaction. The reaction exhibited excellent enantioselectivity, with up to 96 % ee, and good diastereoselectivity, with up to 14 : 1 dr, when employing less sterically hindered secondary phosphines. This particular substrate poses a significant challenge due to its strong poisoning effect in copper catalysis.

Nickel-Catalyzed Enantioselective Alkylation of Primary Phosphines.

Functional molecules derived from stereogenic phosphorus centers have important applications in the discovery of drugs and agrochemicals. They are also widely utilized as chiral ligands or organocatalysts for diverse asymmetric transformations. However, access to P-stereogenic motifs has always been regarded as a highly challenging yet desirable goal in organic synthesis. The development of general and practical methods for the stereoselective construction of synthetically versatile P(III)-stereogenic phosphines is particularly appealing but remains elusive. Herein, we describe a nickel-catalyzed asymmetric alkylation of primary phosphines with alkyl halides for the synthesis of P-stereogenic secondary phosphine-boranes with high enantioselectivity and broad substrate scope. The resulting optically active secondary phosphine-boranes allow for further stereospecific transformations, thereby establishing a modular and efficient platform for the diversity-oriented construction of P-stereogenic phosphine compounds.

Nickel-Catalyzed Asymmetric Arylation of H-Phosphinates

AbstractAn asymmetric arylation of H-phosphinates with aromatic iodo or bromo compounds, catalyzed by cheap and easily available nickel(II) salts, provides access to P-stereogenic phosphinates. This method features mild reaction conditions and a good functional-group compatibility that includes aniline and phenol derivatives.

Synthesis of P-Stereogenic Phosphine Oxides via Nickel-Catalyzed Asymmetric Cross-Coupling of Secondary Phosphine Oxides with Alkenyl and Aryl Bromides.

A general and mild nickel-catalyzed enantioselective C(sp2 )-P cross-coupling for synthesizing P-stereogenic phosphine oxides has been developed. The asymmetric alkenylation/arylation of racemic secondary phosphine oxides with alkenyl/aryl bromides generated P-stereogenic phosphine oxides with high yields and enantioselectivities. Various functional groups were tolerated, and the applications of this method were demonstrated through late-stage functionalization and product transformations.

Pyridine-N-oxide catalyzed acylative desymmetrization of bisphenols: access to P-stereogenic phosphinates with low catalyst loadings

A catalytic stereoselective strategy to access P-stereogenic phosphinates through chiral 4-arylpyridine-N-oxide-catalyzed acylative desymmetrization of bisphenols has been reported.

Palladium-Catalyzed Stereoselective Cleavage of C-P Bond: Enantioselective Construction of Atropisomers Containing a P-Stereogenic Center.

The transition-metal-catalyzed C-P bond cleavage has emerged as a powerful tool for the formation of both C-C and C-P bond. However, the transition-metal-catalyzed stereoselective cleavage of C-P bond is still undeveloped. Herein, we report a palladium-catalyzed stereoselective cleavage of C-P bond for the construction of P-stereogenic phosphines and stereogenic axis. This protocol enables the quick synthesis of atropisomers bearing a P-stereogenic center in high yields, diastereo- and enantioselectivities of up to 98 % ee, >25 : 1 dr. The product is able to serve as chiral catalyst in phosphine catalyzed [3+2] cycloaddition of allenoates to imines, showing the great potential of the present methodology.

Ni-Catalyzed Enantioselective Benzylation of Secondary Phosphine Oxide.

A nickel-catalyzed benzylic substitution of secondary phosphine oxide was described, affording the dialkylated P-stereogenic tertiary phosphine oxides with high to excellent enantioselectivities. The reaction was performed under mild conditions with commercially available benzyl chlorides and bench stable secondary phosphine oxides, exhibiting broad functional group tolerance. It represented a practical example for the preparation of P-stereogenic phosphine compounds.

Ni-catalyzed asymmetric hydrophosphinylation of conjugated enynes and mechanistic studies.

The catalytic asymmetric synthesis of P-stereogenic phosphines is an efficient strategy to access structurally diverse chiral phosphines that could serve as organocatalysts and ligands to transition metals and motifs of antiviral drugs. Herein, we describe a Ni catalyzed highly regio and enantioselective hydrophosphinylation reaction of secondary phosphine oxides and enynes. This method afforded a plethora of alkenyl phosphine oxides which could serve as valuable precursors to bidentate ligands. A new type of mechanism was discovered by combined kinetic studies and density functional theory (DFT) calculations, which was opposed to the widely accepted Chalk–Harrod type mechanism. Notably, the alkene moiety which could serve as a directing group by coordinating with the Ni catalyst in the transition state, plays a vital role in determining the reactivity, regio and enantioselectivity.

Direct visible-light-induced synthesis of P-stereogenic phosphine oxides under air conditions.

Over the past two decades, visible-light-induced transformations have been regarded as being among the most environmentally benign and powerful strategies for constructing complex molecules and diverse synthetic building blocks in organic synthesis. However, the development of efficient photochemical processes for assembling enantiomerically pure molecules remains a significant challenge. Herein, we describe a simple and efficient visible-light-induced C–P bond forming reaction for the synthesis of P-chiral heteroaryl phosphine oxides in moderate to high yields with excellent ee values (97–99% ee). Even in the absence of transition metal or photoredox catalysts, a variety of P-chiral heteroaryl phosphine oxides, including chiral diphosphine oxide 41, have been directly obtained under air conditions. Density functional theory (DFT) calculations have shown that the reaction involves intersystem crossing and single electron transfer to give a diradical intermediate under visible light irradiation.

Nickel-Catalyzed Asymmetric Synthesis of P-Stereogenic Vinyl Phosphines

AbstractAddition reaction to alkynes is an efficient strategy for constructing valuable alkenyl compounds. However, the elusive regioselectivity has been a persistent challenge. In the context of hydrophosphination reaction which could afford valuable P-stereogenic phosphines, the control of enantioselectivity as well as regioselectivity were especially tricky. Here, we highlighted our recent work on the nickel-catalyzed regio- and enantioselective hydrophosphination of unactivated alkynes with in situ generated secondary phosphines.1 Introduction2 Hydrophosphination of Alkynes3 Derivatization Reactions4 Mechanism Research5 Summary and Outlook

Ni-catalyzed highly enantioselective synthesis of sulfur protected P-stereogenic supramolecular phosphine

Ni-catalyzed highly enantioselective synthesis of sulfur protected P-stereogenic supramolecular phosphine

Ni-Catalyzed Enantioselective Allylic Alkylation of H-Phosphinates.

The asymmetric synthesis of P-stereogenic phosphinates through allylic alkylation of H-phosphinates has been developed. With H-phosphinates and allylic acetates as the starting materials, a variety of allylic P-chiral phosphinates were accessed in high enantioselectivities of up to 92% ee and generally high yields. In addition, a further study demonstrated the applicability of this protocol, including the scale-up synthesis and facile transformation of chiral products from phosphinates to phosphine oxides with organolithium reagents under mild reaction conditions.

Copper(I)-Catalyzed Asymmetric Alkylation of Unsymmetrical Secondary Phosphines.

A copper(I)-catalyzed asymmetric alkylation of HPAr1Ar2 with alkyl halides is uncovered, which provides an array of P-stereogenic phosphines in generally high yield and enantioselectivity. The electrophilic alkyl halides enjoy a broad substrate scope, including allyl bromides, propargyl bromide, benzyl bromides, and alkyl iodides. Moreover, 11 unsymmetrical diarylphosphines (HPAr1Ar2) serve as competent pronucleophiles. The present methodology is also successfully applied to catalytic asymmetric double and triple alkylation, and the corresponding products were obtained in moderate diastereo- and excellent enantioselectivities. Some 31P NMR experiments indicate that bulky HPPhMes exhibits weak competitively coordinating ability to the Cu(I)-bisphosphine complex, and thus the presence of stoichiometric HPAr1Ar2 does not affect the enantioselectivity significantly. Therefore, the high enantioselectivity in this reaction is attributed to the high performance of the unique Cu(I)-(R,RP)-TANIAPHOS complex in asymmetric induction. Finally, one monophosphine and two bisphosphines prepared by the present reaction are employed as efficient chiral ligands to afford three structurally diversified Cu(I) complexes, which demonstrates the synthetic utility of the present methodology.

Catalytic Asymmetric Synthesis of P-Stereogenic Phosphines: Beyond Precious Metals

AbstractMetal-catalyzed asymmetric synthesis of P-stereogenic phosphines is a potentially useful approach to a class of chiral ligands with valuable applications in asymmetric catalysis. We introduced this idea with chiral platinum and palladium catalysts, exploiting rapid pyramidal inversion in diastereomeric metal–phosphido complexes (ML*(PRR′)) to control phosphorus stereochemistry. This Account summarizes our attempts to develop related synthetic methods using earth-abundant metals, especially copper, in which weaker metal–ligand bonds and faster substitution processes were expected to result in more active catalysts. Indeed, precious metals were not required. Without any transition metals at all, we exploited related P-epimerization processes to prepare enantiomerically pure phosphiranes and secondary phosphine oxides (SPOs) from commercially available chiral epoxides.1 Introduction2 Copper-Catalyzed Phosphine Alkylation3 Copper-Catalyzed Tandem Phosphine Alkylation/Arylation4 Nickel-Catalyzed Phosphine Alkylation5 Proton-Mediated P-Epimerization in Synthesis of Chiral Phosphiranes6 Diastereoselective Synthesis of P-Stereogenic Secondary Phosphine Oxides (SPOs) from (+)-Limonene Oxide7 Conclusions

Catalytic Enantiodivergent Michael Addition by Subtle Adjustment of Achiral Amino Moiety of Dipeptide Phosphines.

SummaryOver the past decades, asymmetric catalysis has been intensely investigated as a powerful tool for the preparation of numerous chiral biologically active compounds. However, developing general and practical strategies for preparation of both enantiomers of a chiral molecule via asymmetric catalysis is still a challenge, particularly when the two enantiomers of a chiral catalyst are not easily prepared from natural chiral sources. Inspired by the biologic system, we report herein an unprecedented catalytic enantiodivergent Michael addition of pyridazinones to enones by subtle adjustment of achiral amino moiety of dipeptide phosphine catalysts. These two dipeptide phosphine catalysts, P5 and P8, could deliver both enantiomers of a series of N2-alkylpyridazinones in good yields (up to 99%) with high enantioselectivities (up to 99% ee) via the catalyst-controlled enantiodivergent addition of pyridazinones to enones.

Catalytic Asymmetric Diarylphosphine Addition to α-Diazoesters for the Synthesis of P-Stereogenic Phosphinates via P*-N Bond Formation.

The asymmetric catalytic P-H addition of racemic secondary phosphines to electrophilic α-diazoesters via P*-N bond formation is disclosed for the first time. Interaction between the diazoester and the palladium catalyst resulted in the unusually enhanced electrophilic ability of the terminal nitrogen in the diazo functionality, as opposed to the commonly expected formation of a metal carbene by nitrogen elimination. Further derivatization of the generated phosphinic hydrazones provided access to enantioenriched P-stereogenic diarylphosphinates via a simple transformation.

P-Stereogenic Amino-Phosphines as Chiral Ligands: From Privileged Intermediates to Asymmetric Catalysis.

Among chiral phosphines, P-stereogenic phosphines provide unparalleled activity and selectivity and have thus emerged as "state-of-the-art" ligands for asymmetric hydrogenation and other industrially relevant processes. However, the synthesis of this type of ligand implies lengthy multistep sequences, which are a hurdle for many laboratories. There is a lack of methods for the rapid construction of P-stereogenic phosphine ligands. In this respect, P-stereogenic synthons that can be rapidly incorporated into a given ligand scaffold are highly desirable. Over the last 10 years, our group has unveiled that P-stereogenic aminophosphines can be rapidly assembled in a convenient fashion from the corresponding primary aminophosphine and/or the corresponding phosphinous acid.Using cis-1-amino-2-indanol as chiral auxiliary, we devised a multigram synthesis of tert-butylmethylaminophosphine borane and tert-butylmethylphosphinous acid borane, which are key intermediate synthons. Primary aminophosphine works as nucleophilic intermediates at nitrogen. From this synthon, aminodiphosphine (MaxPHOS) and secondary imino phosphoranes (SIP) ligands were synthesized. These ligands exhibit a tautomeric equilibrium between the PH and NH forms, and because of that, they do not undergo oxidation in air. NH/PH tautomerism does not jeopardize their configurational stability, and most importantly, in the presence of a metal source, the equilibrium is shifted toward the NH form, thus allowing coordination through phosphorus. Rh-MaxPHOS and Rh-SIP complexes have been used in asymmetric hydrogenation and [2 + 2 + 2] cycloaddition reactions with outstanding results. On the other hand, P-stereogenic phosphinous acid, upon activation, serves as an electrophilic reagent with amine nucleophiles, allowing SN2 reactions at phosphorus with complete inversion of configuration. This coupling technology exhibits a great potential because it allows the incorporation of the P*-phosphine fragment in numerous ligand structures, provided there is an amino group with which to react. In a mild and efficient process, phosphinous acid has been coupled to hydrazine to yield C2 diphosphines and to chiral benzoimidazole-amines to yield P-stereogenic benzoimidazole-phosphine ligands. The most powerful ligand system, however, arises from the condensation of three independent fragments: our phosphinous acid borane, an amino acid, and an amino alcohol, which yields a library of phosphino-oxazoline ligands named MaxPHOX. The corresponding Ir-MaxPHOX catalyst library was applied with excellent results in the asymmetric hydrogenation of α,β-unsaturated esters, 2-aryl allyl phthalimides, unfunctionalized tetrasubstituted alkenes, cyclic enamides, and N-aryl and N-methyl imines. It also has found application in asymmetric isomerization of alkenes.Overall, we developed key P-stereogenic building blocks that can be incorporated stereospecifically to ligand scaffolds and demonstrated that integration of the P*-aminophosphine fragment in a given catalytic system provides structural diversity that can be a critical contribution to obtaining optimal results and selectivity.

Copper(i)/Ganphos catalysis: enantioselective synthesis of diverse spirooxindoles using iminoesters and alkyl substituted methyleneindolinones.

A copper-catalyzed asymmetric 1,3-dipolar cycloaddition of glycine iminoesters with alkyl substituted 3-methylene-2-oxindoles is described. By using de novo design of P-stereogenic phosphines as ligands, spiro[pyrrolidin-3,3'-oxindole]s are generated in good to excellent yields with high asymmetric induction. A further reduced catalyst loading of 0.1 mol% is sufficient to achieve a satisfactory enantioselectivity of 90% ee. The DFT calculations suggest the second Michael addition of the 1,3-dipole to be the rate- and enantio-determining step. A key feature of this 1,3-dipolar cycloaddition is the wide substrate applicability, even with alkyl aldehyde-derived azomethine ylide; thus it has streamlined a highly enantioselective access to a new class of antiproliferative agents, MDM2-p53.

Palladium-catalyzed asymmetric hydrophosphorylation of alkynes: facile access to P-stereogenic phosphinates.

Despite the importance of P-chiral organophosphorus compounds in asymmetric catalysis, transition metal-catalyzed methods for accessing P-chiral phosphine derivatives are still limited. Herein, a catalytic enantioselective method for the synthesis of P-stereogenic alkenylphosphinates is developed through asymmetric hydrophosphorylation of alkynes. This process is demonstrated for a wide range of racemic phosphinates and leads to diverse P-stereogenic alkenylphosphinates directly.

Enantiodivergent Synthesis of Both PAMPO Enantiomers Using l-Menthyl Chloroacetate and Stereomutation at P in Classical Quaternisation Reactions

A practical protocol for efficient synthesis of both PAMPO enantiomers as well as related functionalised P-stereogenic phosphine oxides in 1–3 steps from effectively resolved (S P)-l-menthyl o-anisyl­-(phenyl)phosphinylacetate has been developed. Examples of non-stereo­selective quaternisation of a tertiary phosphine by alkyl halides have been revealed.