Metal-catalyzed additions of H–P(O) bonds to carbon–carbon unsaturated bonds

Synthesis of alkenylphosphine oxides via Tf2O promoted addition-elimination of ketones and secondary phosphine oxides

Herein, we describe an efficient method for the synthesis of alkenylphosphine oxides via a Tf2O promoted addition-elimination process. Various diarylphosphine oxides and alkylarylphosphine oxides react with ketones smoothly and produce alkenylphosphine oxides in moderate to excellent yields with abundant functional group compatibility. In addition, several transformations and applications of the product also demonstrate the potential value of the methodology.

Reductive Coupling of P(O)-H Compounds and Aldehydes for the General Synthesis of Phosphines and Phosphine Oxides

A novel strategy for the selective construction of a C(sp3)-P(III) or -P(V) bond from >P(O)-H compounds and aldehydes is disclosed. By using the H3PO3/I2 system, various secondary phosphine oxides could react with both aromatic and aliphatic aldehydes to afford valuable phosphines (isolated as sulfides) and phosphine oxides in good yields. This method features a wide substrate scope and simple reaction conditions and avoids the use of toxic halides and metals.

Preparation of Vinylphosphonates from Ketones Promoted by Tf2O

An efficient triflic anhydride promoted phosphorylation of ketone was disclosed, and vinylphosphorus compounds were prepared under solvent- and metal-free conditions. Both aryl and alkyl ketones could perform smoothly to give vinyl phosphonates in high to excellent yields. In addition, the reaction was easy to carry out and easy to scale up. Mechanistic studies suggested that this transformation might involve nucleophilic vinylic substitution or a nucleophilic addition-elimination mechanism.

Sustainable Production of Reduced Phosphorus Compounds: Mechanochemical Hydride Phosphorylation Using Condensed Phosphates as a Route to Phosphite

In pursuit of a more sustainable production of phosphorous acid (H₃PO₃), a versatile chemical with phosphorus in the +3 oxidation state, we herein report that condensed phosphates can be employed to phosphorylate hydride reagents under solvent-free mechanochemical conditions to furnish phosphite (HPO₃ ^2-). Using potassium hydride as the hydride source, sodium trimetaphosphate (Na₃P₃O₉), triphosphate (Na₅P₃O₁₀), pyrophosphate (Na₄P₂O₇), fluorophosphate (Na₂PO₃F), and polyphosphate ("(NaPO₃) _n ") engendered phosphite in optimized yields of 44, 58, 44, 84, and 55% based on total P content, respectively. Formation of overreduced products including hypophosphite (H₂PO₂ ^-) was identified as a competing process, and mechanistic investigations revealed that hydride attack on in-situ-generated phosphorylated phosphite species is a potent pathway for overreduction. The phosphite generated from our method was easily isolated in the form of barium phosphite, a useful intermediate for production of phosphorous acid. This method circumvents the need to pass through white phosphorus (P₄) as a high-energy intermediate and mitigates involvement of environmentally hazardous chemicals. A bioproduced polyphosphate was found to be a viable starting material for the production of phosphite. These results demonstrate the possibility of accessing reduced phosphorus compounds in a more sustainable manner and, more importantly, a means to close the modern phosphorus cycle.

Palladium-Catalyzed C-P(III) Bond Formation by Coupling ArBr/ArOTf with Acylphosphines

Palladium-catalyzed C-P bond formation reaction of ArBr/ArOTf using acylphosphines as differential phosphination reagents is reported. The acylphosphines show practicable reactivity with ArBr and ArOTf as the phosphination reagents, though they are inert to the air and moisture. The reaction affords trivalent phosphines directly in good yields with a broad substrate scope and functional group tolerance. This reaction discloses the acylphosphines' capability as new phosphorus sources for the direct synthesis of trivalent phosphines.

Heterogeneous Catalytic Method for the Copper(II)-Catalysed Addition of H-Phosphinates and Secondary Phosphine Oxides to Phenylacetylene

Copper(II) on 4 Å molecular sieve was found to be an efficient heterogeneous catalyst in the addition of different H-phosphinates and secondary phosphine oxides to phenylacetylene. All hydrophosphinylation reactions were completely regioselective, as only β-isomers were formed, and the E-alkenylphosphinates and E-alkenylphosphine oxides were synthesized in moderate to excellent yields. The catalyst could be reused multiple times in the reaction.

Graphic Abstract

Alkene homologation via visible light promoted hydrophosphination using triphenylphosphonium triflate

A hydrophosphination reaction of alkenes with triphenylphosphonium triflate under photocatalytic conditions is described. The reaction is promoted by naphthalene-fused N-acylbenzimidazole and is believed to proceed through intermediate formation of a phosphinyl radical cation. The resulting phosphonium salts are directly involved in the Wittig reaction leading to homologated alkenes.

Boron Lewis Acid-Catalyzed Hydrophosphinylation of N-Heteroaryl-Substituted Alkenes with Secondary Phosphine Oxides

We report the boron-catalyzed hydrophosphinylation of N-heteroaryl-substituted alkenes with secondary phosphine oxides that furnishes various phosphorus-containing N-heterocycles. This process proceeds under mild conditions and enables the introduction of a phosphorus atom into multisubstituted alkenylazaarenes. The available mechanistic data can be explained by a reaction pathway wherein the C-P bond is created by the reaction between the activated alkene (by coordination to a boron catalyst) and the phosphorus(III) nucleophile (in tautomeric equilibrium with phosphine oxide).

Synthesis of a Bolaamphiphilic Alkenyl Phosphonic Acid by Ru-catalyzed Olefin Cross Metathesis Reaction

We report the synthesis of bolaamphiphilic alkenyl phosphonic acid (BPC₁₂) through the olefin crossmetathesis reaction of vinylphosphonic acid with 1,11-dodecadiene in the presence of a Ru-carbene catalyst. BPC₁₂ possesses two trans-P-C=C moieties and is thus readily soluble in water up to 3.4 g L^-1, as confirmed by ¹H nuclear magnetic resonance (NMR) measurements. Surface tension measurements revealed that BPC₁₂ reduced the surface tension of water from 72.0 to 47.0 mN m^‒1. The occupied area per molecule at the air/water interface (A) of BPC₁₂ (216 Ų) was ten times larger than that of dodecenyl phosphonic acid PC₁₂ (23 Ų). Moreover, dynamic light scattering measurement of an aqueous BPC₁₂ solution (5 mM) revealed the formation of large aggregates with an average diameter of 81.8±27.0 nm.

Cross-Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

Alkynes are among the most fundamentally important organic compounds and are widely used in synthetic chemistry, biochemistry, and materials science. Thus, the development of an efficient and sustainable method for the preparation of alkynes has been a central concern in organic synthesis. Cross-dehydrogenative coupling utilizing E-H and Z-H bonds in two different molecules can avoid the need for prefunctionalization of starting materials and has become one of the most straightforward methods for the construction of E-Z chemical bonds. This Review summarizes recent progress in the preparation of internal alkynes by cross-dehydrogenative coupling with terminal alkynes.

Construction of P-Chiral Alkenylphosphine Oxides through Highly Chemo-, Regio-, and Enantioselective Hydrophosphinylation of Alkynes

Alkenylphosphine oxides have a wide spectrum of practical applications. However, chemo-, regio-, and enantiocontrolled construction of this structural motif still constitutes a significant synthetic challenge. Here we show that these compounds can be efficiently accessed by using a palladium/Xiao-Phos catalytic system, which leads to the highly regioselective formation of the anti-Markovnikov adducts through addition of a secondary phosphine oxide to an alkyne. Diverse (hetero)aryl and alkyl alkynes, as well as both terminal and internal alkynes can be employed as substrates. The kinetic resolution process makes it possible to produce alkenylphosphine oxide and recovered secondary phosphine oxides with high ee values. Further transformations of these two P-chiral scaffolds confirm the high practicability and application prospect of our synthetic strategies. Initial mechanistic studies strongly suggested that hydropalladation is likely responsible for the conversion process.

Conversion of triphenylphosphine oxide to organophosphorus via selective cleavage of C-P, O-P, and C-H bonds with sodium

For over half a century, thousands of tons of triphenylphosphine oxide Ph₃P(O) have been produced every year from the chemical industries as a useless chemical waste. Here we disclose efficient transformations of Ph₃P(O) with cheap resource-abundant metallic sodium finely dispersed in paraffin oil. Ph₃P(O) can be easily and selectively transformed to three reactive organophosphorus intermediates-sodium diphenylphosphinite, sodium 5H-benzo[b]phosphindol-5-olate and sodium benzo[b]phosphindol-5-ide-that efficiently give the corresponding functional organophosphorus compounds in good yields. These functional organophosphorus compounds are difficult to prepare but highly industrially useful compounds. This may allow Ph₃P(O) to be used as a precious starting material for highly valuable phosphorus compounds.

Copper-catalyzed tandem phosphorylative allenylation/cyclization of 1-(o-aminophenyl)prop-2-ynols with the P(O)–H species: access to C2-phosphorylmethylindoles

A novel method to synthesize C2-phosphorylmethylindoles via the carbocation formation initiated tandem phosphorylative allenylation/cyclization of 1-(o-aminophenyl)prop-2-ynols with the P(O)–H species has been developed.

Phospha-Michael reaction of tertiary phosphanes Ph2P–X (X=SiMe3, Cl) and N-triflyl-propiolamides

The uncatalyzed silylphosphanylation of acetylenic N-trifluoromethylsulfonyl-carboxamides by Ph2P–SiMe3, formally an insertion of a C,C triple bond into a P–Si bond, is reported. Some characteristic functional group transformations of the resulting 3-PPh2-2-SiMe3-N-triflyl-acrylamides were briefly explored: transamidation of the N-triflylamide group with allylamine, P oxidation and protodesilylation. A hydrophosphorylation of the acetylenic triple bond with chloro(diphenyl)phosphane is also reported.

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

The facile synthesis of organophosphorus compounds is of great importance for the development of new synthetic methods by using air-stable sources of phosphorus. In this respect, a synthetic method that is based on a reductive rearrangement and is capable of converting air-stable pentavalent phosphorus compounds into reactive trivalent phosphorus compounds is a powerful tool. Tetraphenyldiphosphine disulfide, which is a shelf-stable solid, was the focus of this study, and it was shown to undergo reductive rearrangement to trigger the bisthiophosphinylation of a variety of alkenes, such as terminal, cyclic, internal, and branched alkenes, 1,3-dienes, and terminal alkynes when exposed to light without any catalyst, base, or additive.

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds

A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [( p- tBu-C₆H₄)₂CH]₂M(L _n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI₂(THF) _n ( n = 0-2) and [( p- tBu-C₆H₄)₂CH]^-Na⁺. In complex 1, the benzhydryl ligands are bound to the metal center in η²-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η³-fashion. In complex 2, one ligand is η³-coordinated while the second one is η⁴-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C₆D₆ at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C₆D₆ solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 °C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH₂ toward the internal C═C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph₂PH and PhPH₂ was realized due to the application of Yb(II) complex as a catalyst.

Synthesis of Bis(phosphanyl)alkane Monosulfides by the Addition of Diphosphane Monosulfides to Alkenes under Light

Bis-phosphanated compounds are regarded as the most ubiquitous privileged ligand structures in transition-metal catalysis. The development of highly atom economical reactions is of great importance for their syntheses because less atom economical methods often require complicated purification procedures under inert atmospheres to remove excess starting materials and byproducts. Herein, the photoinduced addition reactions of diphosphane monosulfides bearing P^V (S)-P^III single bonds to alkenes is disclosed. These reactions require only equimolar amounts of the diphosphane monosulfide relative to the alkene and facilitate highly selective introduction of two different types of phosphorus-containing groups, such as thiophosphoryl and phosphanyl groups, into a variety of alkenes without any catalyst, base, or additive.

Zinc-catalyzed regioselective C–P coupling of p-quinol ethers with secondary phosphine oxides to afford 2-phosphinylphenols

A highly regioselective C–P coupling reaction of p-quinol ethers with secondary phosphine oxides is developed as a new synthesis method for 2-phosphinylphenols by using Zn(OTf)₂ as the catalyst.

Enantiodivergent synthesis of 1,2-bis(diphenylphosphino)ethanes via asymmetric [3 + 2]-cycloaddition

The present work provides efficient access to chiral 1,2-bis(diphenylphosphino)ethanes (DPPEs) directly from diphosphine oxide alkenes and azomethine ylides via asymmetric [3 + 2] cycloaddition. Both enantiomers of the products can be obtained in good to excellent diastereo- and enantioselectivities (up to >20 : 1 dr and 99% ee).

Enantioselective Coupling of Dienes and Phosphine Oxides

We report a Pd-catalyzed intermolecular hydrophosphinylation of 1,3-dienes to afford chiral allylic phosphine oxides. Commodity dienes and air stable phosphine oxides couple to generate organophosphorus building blocks with high enantio- and regiocontrol. This method constitutes the first asymmetric hydrophosphinylation of dienes.

Decarboxylative cross-coupling reactions for P(O)-C bond formation

Phosphorus-containing compounds are one of the most important classes of organic compounds, which have wide applications in organic chemistry, medicinal chemistry, agricultural chemistry, and materials chemistry. In particular, organophosphorus compounds bearing a P(O)-C bond have attracted significant attention in recent decades due to their widespread biological and pharmacological activities. In this review, we will highlight the most important developments in the construction of P(O)-C bonds through decarboxylative C-P cross-coupling reactions. The literature has been surveyed from 2011 to May 2018.

Direct C-OH/P(O)-H dehydration coupling forming phosphine oxides

A t-BuONa-mediated C-OH/P(O)-H cross dehydration coupling to produce alkylphosphine oxides is developed. This reaction employed readily available alcohols and P(O)-H compounds as the starting materials, providing an efficient alternative method for constructing sp3 C-P bonds. A reasonable reaction path involving dehydration and subsequent regio-selective hydrophosphorylation of the resulting alkenes was proposed.

Palladium-catalysed coupling of α-halo vinylphosphonate and α-phosphonovinyl sulfonate with alkylzincs: straightforward and versatile synthesis of α-alkyl vinylphosphonates

Easy and efficient access to α-alkylated vinylphosphonates via Pd-catalysed Negishi coupling!

Eosin Y-catalyzed, visible-light-promoted carbophosphinylation of allylic alcohols via a radical neophyl rearrangement

An eosin Y-catalyzed, visible-light-promoted phosphinylation-induced 1,2-rearrangement reaction of allylic alcohols to prepare various β-aryl-γ-ketophosphine oxides is presented.