A novel and convenient preparation of hypophosphite esters

Hypophosphite addition to alkenes under solvent-free and non-acidic aqueous conditions

Hypophosphite adds to alkenes in high yields under solvent-free conditions at elevated temperature, including α,β-unsaturated carboxylates. The reaction proceeds by a radical mediated pathway. Hypophosphite addition is also effective under non-acidic aqueous conditions employing radical initiators. These methods complement other hypophosphite addition reactions and simplify the synthesis of polyfunctional H-phosphinates.

Let's Make White Phosphorus Obsolete

Industrial and laboratory methods for incorporating phosphorus atoms into molecules within the framework of Green Chemistry are in their infancy. Current practice requires large inputs of energy, involves toxic intermediates, and generates substantial waste. Furthermore, a negligible fraction of phosphorus-containing waste is recycled which in turn contributes to negative environmental impacts, such as eutrophication. Methods that begin to address some of these drawbacks are reviewed, and some key opportunities to be realized by pursuing organophosphorus chemistry under the principles of Green Chemistry are highlighted. Methods used by nature, or in the chemistry of other elements such as silicon, are discussed as model processes for the future of phosphorus in chemical synthesis.

UV-mediated hydrophosphinylation of unactivated alkenes with phosphinates under batch and flow conditions

A UV-mediated hydrophosphinylation of unactivated alkenes with H-phosphinates and hypophosphorous acid under radical free conditions is presented. The reaction affords selectively a large number of structurally diverse organophosphorous compounds in moderate to good yields under mild reaction conditions in the presence of an organic sensitizer as catalyst irradiated by UV-A LEDs. Furthermore, the high yielding hydrophosphinylation in continuous flow is disclosed.

First principles optimally tuned range-separated density functional theory for prediction of phosphorus–hydrogen spin–spin coupling constants

The novel optimally tuned range-separated approximations for predicting NMR spin–spin coupling constants are proposed and benchmarked numerically.

Recent advances in H-phosphonate chemistry. Part 1. H-phosphonate esters: synthesis and basic reactions

This review covers recent progress in the preparation of H-phosphonate mono- and diesters, basic studies on mechanistic and stereochemical aspects of this class of phosphorus compounds, and their fundamental chemistry in terms of transformation of P-H bonds into P-heteroatom bonds. Selected recent applications of H-phosphonate derivatives in basic organic phosphorus chemistry and in the synthesis of biologically important phosphorus compounds are also discussed.

In search of the appropriate theoretically justified mixing coefficient in parameter-free hybrid functionals for computing the NMR parameters

The parameter-free hybrid density functionals, with theoretically justified mixing coefficients, are recommended to predict the NMR parameters.

Phosphinate chemistry in the 21st century: a viable alternative to the use of phosphorus trichloride in organophosphorus synthesis

Organophosphorus compounds are important in everyday applications ranging from agriculture to medicine and are used in flame retardants and other materials. Although organophosphorus chemistry is known as a mature and specialized area, researchers would like to develop new methods for synthesizing organophosphorus compounds to improve the safety and sustainability of these chemical processes. The vast majority of compounds that contain a phosphorus-carbon bond are manufactured using phosphorus trichloride (PCl3) as an intermediate. However, these reactions require chlorine, and researchers would like to avoid the use of PCl3 and develop safer chemistry that also decreases energy consumption and minimizes waste. Researchers have already proposed and discussed two primary strategies based on elemental phosphorus (P4 or Pred) or on phosphine (PH3) as alternatives to PCl3. However, phosphinates, an important class of phosphorus compounds defined as any compound with a phosphorus atom attached to two oxygens, R(1)R(2)P(O)(OR) (R(1)/R(2) = hydrogen/carbon), offer another option. This Account discusses the previously neglected potential of these phosphinates as replacements of PCl3 for the preparation of organophosphorus compounds. Because of their strong reductive properties, industry currently uses the simplest members of this class of compounds, hypophosphites, for one major application: electroless plating. In comparison with other proposed PCl3 surrogates, hypophosphorous derivatives can offer improved stability, lower toxicity, higher solubility, and increased atom economy. When their reducing power is harnessed to form phosphorus-carbon or phosphorus-oxygen bonds, these compounds are also rich and versatile precursors to organophosphorus compounds. This Account examines the use of transition metal-catalyzed reactions such as cross-coupling and hydrophosphinylation for phosphorus-carbon bond formation. Because the most important industrial organophosphorus compounds include compounds triply or quadruply bound to oxygen, I also discuss controlled transfer hydrogenation for phosphorus-oxygen bond formation. I hope that this Account will further promote research in this novel and exciting yet much underdeveloped area of phosphinate activation.

Inhibition of glutamate racemase by substrate-product analogues

D-Glutamate is an essential biosynthetic building block of the peptidoglycans that encapsulate the bacterial cell wall. Glutamate racemase catalyzes the reversible formation of D-glutamate from L-glutamate and, hence, the enzyme is a potential therapeutic target. We show that the novel cyclic substrate-product analogue (R,S)-1-hydroxy-1-oxo-4-amino-4-carboxyphosphorinane is a modest, partial noncompetitive inhibitor of glutamate racemase from Fusobacterium nucleatum (FnGR), a pathogen responsible, in part, for periodontal disease and colorectal cancer (Ki=3.1±0.6 mM, cf. Km=1.41±0.06 mM). The cyclic substrate-product analogue (R,S)-4-amino-4-carboxy-1,1-dioxotetrahydro-thiopyran was a weak inhibitor, giving only ∼30% inhibition at a concentration of 40 mM. The related cyclic substrate-product analogue 1,1-dioxo-tetrahydrothiopyran-4-one was a cooperative mixed-type inhibitor of FnGR (Ki=18.4±1.2 mM), while linear analogues were only weak inhibitors of the enzyme. For glutamate racemase, mimicking the structure of both enantiomeric substrates (substrate-product analogues) serves as a useful design strategy for developing inhibitors. The new cyclic compounds developed in the present study may serve as potential lead compounds for further development.

Evaluation of Approximate Exchange-Correlation Functionals in Predicting One-Bond (31)P-(1)H NMR Indirect Spin-Spin Coupling Constants

This work benchmarks density functional theory, with several different exchange-correlation functionals, for prediction of isotropic one-bond phosphorus-hydrogen NMR spin-spin coupling constants (SSCCs). Our test set consists of experimental SSCCs from 30 diverse molecules representing multiple phosphorus bonding environments. The results suggest the importance of a balance between the choice of correlation functional and the admixture of nonlocal exchange. Overall, standard DFT methods appear to suffice for usefully accurate predictions of (31)P-(1)H SSCCs.

Insights into a surprising reaction: the microwave-assisted direct esterification of phosphinic acids

It is well-known that phosphinic acids do not undergo direct esterifications with alcohols under thermal conditions. However, the esterifications take place under microwave (MW) irradiation due to the beneficial effect of MW. As a comparison, maximum 12-15% conversions were observed on traditional heating. It was proved experimentally that the MW-assisted esterifications are not reversible under the conditions applied that may be the consequence of the hydrophobic medium established by the long chain alcohol/phosphinic ester. Neither the thermodynamic, nor the kinetic data obtained by high level quantum chemical calculations justify the direct esterification of phosphinic acids under thermal conditions. The thermodynamic data show that there is no driving force for the reactions under discussion. As a consequence of the relatively high values of activation enthalpy (102-161 kJ mol(-1)), these esterifications are controlled kinetically. Comparing the energetics of the esterification of phosphinic acids and the preparative results obtained under MW conditions, one can see the potential of the MW technique in the synthesis of phosphinates. During our study, a series of new cyclic phosphinates with lipophilic alkyl groups was synthesized.

Strategies for the asymmetric synthesis of H-phosphinate esters

Access to P-chiral H-phosphinates via desymmetrization of hypophosphite esters was investigated. The use of chiral auxiliaries, chiral catalysts, and of a bulky prochiral group that could lead to kinetic resolution was explored. A chiral NMR assay for enantiomeric excess determination of H-phosphinates was developed. An asymmetric route to C-chiral H-phosphinates is also examined and an assay was developed.

Borane Complexes of the H(3)PO(2) P(III) Tautomer: Useful Phosphinate Equivalents

The preparation and reactivity of novel (R(1)O)(R(2)O)P(BH(3))H [R(1), R(2) = Et, TIPS] synthons is investigated. The direct alkylation of these compounds with lithium hexamethyldisilazide (LiHMDS) and various electrophiles, provided new series of phosphonite-borane complexes, which can be converted into H-phosphinates and boranophosphonates.

Recent Developments in the Addition of Phosphinylidene-Containing Compounds to Unactivated Unsaturated Hydrocarbons: Phosphorus-Carbon Bond-Formation via Hydrophosphinylation and Related Processes

The reactions of phosphinylidene-containing compounds with unactivated unsaturated hydrocarbons are reviewed. The review is organized by phosphorus-containing functional group types. Free-radical and metal-catalyzed additions of R(1)R(2)P(O)H to alkenes, alkynes, and related compounds, deliver functionalized organophosphorus compounds RP(O)R(1)R(2), including H-phosphinates, phosphinates, tertiary phosphine oxides, and phosphonates. The review covers the literature up to February 2008.

Synthesis of and evaluation of lipid A modification by 4-substituted 4-deoxy arabinose analogs as potential inhibitors of bacterial polymyxin resistance

Three sets of novel 4-deoxy-l-arabinose analogs were synthesized and evaluated as potential inhibitors of the bacterial resistance mechanism in which lipid A, on the outer membrane, is modified with 4-amino-4-deoxy-l-arabinose (l-Ara4N). One compound diminished the transfer of l-Ara4N onto lipid A. These results suggest that small molecules might be designed that would effect the same reversal of bacterial resistance observed in genetic knockouts.

Palladium-catalyzed dehydrative allylation of hypophosphorous acid with allylic alcohols

A novel palladium-catalyzed allylation of H3PO2 with allylic alcohols is described. The phosphorus-carbon bond-forming reaction produces allylic-H-phosphinic acids and water, in the absence of additives. Primary H-phosphinic acids are obtained in excellent yields, whereas secondary H-phosphinic acids react sluggishly. A reusable polymer-supported catalyst is also described. The reaction provides an environmentally sound approach to H-phosphinic acids.

NiCl2-catalyzed hydrophosphinylation

[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating.

Palladium-catalyzed hydrophosphinylation of alkenes and alkynes

Various palladium catalysts promote the addition of hypophosphorous derivatives ROP(O)H(2) to alkenes and alkynes in good yields and under mild conditions. Particularly, Cl(2)Pd(PPh(3))(2)/2 MeLi, and Pd(2)dba(3)/xantphos allow for phosphorus-carbon bond formation instead of transfer hydrogenation. Commercial aqueous solutions of hypophosphorous acid can be employed successfully at ambient temperature. With styrene and terminal alkynes, the regioselectivity (linear versus branched products) can be controlled to some extent with the catalytic system employed. The methodology considerably extends upon previous routes for the preparation of H-phosphinic acids and other organophosphorus compounds.