Preparation of Optically Pure Tertiary Phosphine Oxides via the Addition of P-Stereogenic Secondary Phosphine Oxide to Activated Alkenes

Functionalized P,C-stereogenic tertiary phosphine oxides were prepared by the addition of (RP)-menthyl phenylphosphine oxide to activated olefins, in high drP and drC, and were isolated in excellent yields. The reaction was readily catalyzed by Ca(OH)2 or occurred with gentle heating. A wide range of substrates, including vinyl ketones, esters, nitriles, and nitro alkenes, can be used in the reaction.

General synthesis of P-stereogenic compounds: the menthyl phosphinate approach

Easily prepared menthyl phosphinates of high diastereoisomeric purity provide versatile intermediates for the synthesis of P-stereogenic compounds.

Mechanism of phosphine borane deprotection with amines: the effects of phosphine, solvent and amine on rate and efficiency

The kinetics of borane transfer from simple tertiary phosphine borane adducts to a wide range of amines have been determined. All data obtained, including second-order kinetics, lack of cross-over, and negative entropies of activation for reaction of triphenylphosphine borane with quinuclidine and triethylamine, are consistent with a direct (SN 2-like) transfer process, rather than a dissociative (SN 1-like) process. The identities of the amine, phosphine, and solvent all impact substantially on the rate (k) and equilibrium (K) of the transfer, which in some cases vary by many orders of magnitude. P-to-N transfer is more efficient with cyclic amines in apolar solvents due to reduced entropic costs and ground-state destabilisation. Taken as a whole, the data allow informed optimisation of the deprotection step from the stand-point of rate, or synthetic convenience. In all cases, both reactants should be present at high initial concentration to gain kinetic benefit from the bimolecularity of the process. Ultimately, the choice of amine is dictated by the identity of the phosphine borane complex. Aryl-rich phosphine boranes are sufficiently reactive to allow use of diethylamine or pyrrolidine as a volatile low polarity solvent and reactant, whereas more alkyl-rich phosphines benefit from the use of more reactive amines, such as 1,4-diaza[2.2.2]bicyclooctane (DABCO), in apolar solvents at higher temperatures.

Chemoselective reduction of the phosphoryl bond of O-alkyl phosphinates and related compounds: an apparently impossible transformation

A method is reported for the phosphoryl bond cleavage of O-alkyl phosphinates, phosphinothioates and certain phosphonamidates to furnish the corresponding P(iii) borane adducts.

Reduction of secondary and tertiary phosphine oxides to phosphines

In this review, we summarise all the methods of phosphine oxide reduction and discuss their mechanistic aspects.

The synthesis of heteroleptic phosphines

This perspective presents an overview of modern synthetic approaches to heteroleptic phosphines.

Efficient synthesis of P-chiral biaryl phosphonates by stereoselective intramolecular cyclization

A series of P-chiral biaryl phosphonates were efficiently synthesized from diaryl 2-bromo arylphosphonates in high yields (up to 92%) and good enantioselectivities (up to 88% ee) through a palladium-catalyzed desymmetric intramolecular cyclization with a P-chiral biaryl monophosphorus ligand.

Gilheany D. First ever observation of the intermediate of phosphonium salt and ylide hydrolysis: P-hydroxytetraorganophosphorane

P-Hydroxytetraorganophosphorane, the putative intermediate in phosphonium salt & ylide hydrolysis reactions, has been observed and characterised for the first time, thus establishing unequivocally its existence & involvement in these reactions.

Synthetic and structural study of the coordination chemistry of a peri-backbone-supported phosphino-phosphonium salt

Coordination chemistry of an acenaphthene peri-backbone-supported phosphino-phosphonium chloride (1) was investigated, revealing three distinct modes of reactivity. The reaction of 1 with Mo(CO)4(nor) gives the Mo(0) complex [(1)Mo(CO)4Cl] (2), in which the ligand 1 exhibits monodentate coordination through the phosphine donor and the P-P bond is retained. PtCl2(cod) reacts with the chloride and triflate salts of 1 to form a mononuclear complex [(1Cl)PtCl2] (3) and a binuclear complex [((1Cl)PtCl)2][2TfO] (4), respectively. In both of these complexes, the platinum center adds across the P-P bond, and subsequent chloride transfer to the phosphenium center results in phosphine-chlorophosphine bidentate coordination. [((1)PdCl)2] (5) was isolated from the reaction of 1 and Pd2(dba)3 (dba = dibenzylideneacetone). Oxidative addition to palladium(0) results in a heteroleptic phosphine bridging phosphide coordination to the Pd(II) center. In addition, reaction of 1 with BH3·SMe2 leads to the bis(borane) adduct of the corresponding mixed tertiary/secondary phosphine (6), with BH3 acting as both a reducing agent and a Lewis acid. The new compounds were fully characterized, including X-ray diffraction. The ligand properties of 1 and related bonding issues are discussed with help of DFT computations.

A Convenient Synthetic Protocol to 1,2-Bis(dialkylphosphino)ethanes

1,2-Bis(dialkylphosphino)ethanes are readily prepared from the parent phosphine oxides, via a novel sodium aluminium hydride/sodium hydride reduction protocol of intermediate chlorophosphonium chlorides. This approach is amenable to multi-gram syntheses, utilises readily available and inexpensive reagents, and benefits from a facile non-aqueous work-up in the final reductive step.

Development of a redox-free Mitsunobu reaction exploiting phosphine oxides as precursors to dioxyphosphoranes

The development of a redox-free protocol for Mitsunobu inversion is described.

Organophosphorus catalysis to bypass phosphine oxide waste

The conversion of oxygen-containing compounds is often achieved by the use of phosphorus reagents. The newly formed phosphine oxide bond delivers the enthalpic gain that drives reactions, such as the Wittig, Mitsunobu, and Appel reaction, to completion. However, phosphine oxides are recognized as undesirable waste products and in the past decade several methods have emerged that address this issue by in situ regeneration of the phosphorus reagent. This Minireview outlines the two distinct strategies and underpinning research that led to these advances. The potential of the emerging field of phosphorus catalysis in chemistry is shown and new developments that may stimulate further research are described.