Phosphorus nucleophilic reactivity

Taira, K., Mock, W. L., Gorenstein, D. G. (1984). Experimental tests of the stereoelectronic effect at phosphorus nucleophilic reactivity of phosphite esters. Journal of the American Chemical Society, 106,7831-7835... 

B. Aryl Derivatives.—The Ph3P=N group imparts high nucleophilic reactivity to the tervalent phosphorus atom in A -(diphenylphosphino)tri-phenylphosphazene, Ph3p=N PPha- Ready reactions occur with methyl iodide, phosphorus(in) halides, and bromine ... 

Compared with the variety of existing carbon or nitrogen nucleophiles that were subjected to nucleophilic addition to there are few examples for phosphorus nucleophiles. Neutral trialkylphosphines turn out to be to less reactive for an effective addihon to Cjq even at elevated temperatures [114], Trialkylphosphine oxides show an increased reactivity. They form stable fullerene-substituted phosphine oxides [115] it is not yet clear if the reaction proceeds via a nucleophilic mechanism or a cycloaddition mechanism. Phosphine oxide addition takes place in refluxing toluene [115], At room temperature the charge-transfer complexes of with phosphine oxides such as tri-n-octylphosphine oxide or tri-n-butylphosphine oxide are verifiable and stable in soluhon [116],... 

J. Shaskus and P. Haake, Ascorbic acid. 2. Nucleophilic reactivity of ascorbate anion towards acyl carbon and phosphorus, J. Org. Chem., 49 (1984) 197-199. 

White phosphorus, a strained tricyclic system has a low nucleophilic reactivity but is highly electrophilic. 2) Attack by a nucleophile produces a reactive phosphide ion which is rapidly protonated in hydroxylic media. For high yields of a required product it is essential to trap this ion with a suitable electrophile. 3) Owing to the mutual reaction of nucleophile and electrophile the number of useful combinations is limited. In principle a combination of hard nucleophile and soft electrophile is preferred. 

To get a broader concept of the nucleophilic reactivity of phosphorus acid derivatives towards organosilanes we studied mechanism of reactions of triorganosilyl halides with esters of tricoordinate and tetracoordinate phosphorus having the general formulae ... 

It seems likely that the magnitude of p represents the "extent of electron demand at phosphorus , in the T. S. or in other words is a measure of "electron transfer" in the T.S., a term (=z) which appears in the semi-empirical equations describing the nucleophilic reactivity of tricoordinated phosphorus. This concept is reinforced by (i) the observation (from the data of Bokonov. and Goetz ) that p-values based on the pKg values of protonated phosphines increase with increasing pKa, i.e. increase with a shift of the equilibrium (eqn. 4) to the left and... 

Since sulfonation of pyridine iV-oxide is about as difficult as is that of pyridine itself and takes place at the 3-position,17 it has been assumed18 that, in fuming sulfuric acid, pyridine iV-oxide reacts only in the salt form (3), when the prediction is that substitution at C-3 would take place. It is, however, difficult to account for the fact that bromination, even at 110° in the presence of iron powder, does not occur.17 Bromination in chloroform solution in the presence of acetic anhydride and sodium acetate (when the O-acetate is the the probable substrate) take place readily, however, to give 3,5-dibromopyridine JV-oxide.19 The predicted order of nucleophilic reactivity, on the basis of both atom localization energies and ground-state v-electron density calculations, is 4 > 2 > 3. The same order is predicted for the nucleophilic substitution reactions of the salts of pyridine JV-oxide. In actual practice, iV-alkoxypyridinium derivatives undergo nucleophilic attack preferentially at C-2.20-23 The reaction of some pyridine iV-oxides with phosphorus pentachloride may involve the formation... 

The nucleophilic reactivity of the C-5 oxygen is well documented however, no quantitative data are available. A-2-Thiazoline-5-ones (212) react at oxygen with acetyl chloride or acetic anhydride (447. 452). benzoyl chloride (447). methyl or phenyl isocyanate (467). carbamoyl chloride (453, 467). or phosphorus derivatives (468, 428) in the presence of bases to give 213, 214. 215. or 216 (Scheme 109). Strong bases such as... 

Reactions of vinyliodonium salts with nitrogen, oxygen, sulfur and phosphorus nucleophiles have been reported only sporadically and have not been examined in a systematic way. The earliest studies are qualitative, while later investigations are based on rather atypical vinyliodonium structures. Such reactions usually result in the replacement of iodobenzene by the nucleophile (equation 184). The MC pathway, a common mode of reactivity for alkynyliodonium salts, has not been documented for any vinyliodonium compound. 

A fundamental route for the preparation of simple tetraalkylphosphonium salts is the reaction of a tertiary phosphine with a haloalkane or other substrate upon which a simple nucleophilic substitution reaction can occur. (In comparing phosphorus nucleophiles with the corresponding nitrogen-centered nucleophiles, it must be remembered that the phosphorus is significantly more nucleophilic than is the nitrogen. For example, while triphenylamine is devoid of nucleophilic character in reaction with ordinary haloalkanes, triphenylphosphine exhibits high reactivity.) Reactivity of the phosphorus in such nucleophilic substitution reactions, as with other types of nucleophiles, decreases with increasing substitution about the electrophilic site of the substrate. 

Whether one looks at C or X attack, the data given in Table 24 suggest that polarizability or the softness factor is important in determining nucleophilicity. Phosphorus nucleophiles appear to be more reactive than structurally similar nitrogen nucleophiles, e.g. with chlorophenylacetylene, A (Bu3P, DMF)/A (TED, MeCN) = 260 at 30 °C As compared with oxygen, sulphur compounds are... 

Preparation and Structure.—A -Ray crystal structures of benzoylmethylene-triphenylphosphorane (1) and arsorane (2) suggest that the phosphorus ylidic bond has more double bond character, which is in agreement with the greater nucleophilic reactivity of (2). P-Chloroalkylidenephosphorane (3) and (a-chloro-alkyl)phosphine (4) isomers undergo substituent-dependent interconversion by intramolecular 1,2-chlorine shift. ... 

Depending on their reactivity towards carbonyl components, the phosphorus ylides can be classified into three groups [3,5]. When R and/or R is an electron donor, e.g. an alkyl group, the nucleophilicity of the ylide, and thus its reactivity towards carbonyl groups, are increased. These ylides are termed reactive or non-stabilized . Strongly electron-withdrawing groups such as esters, nitriles, and ketones, on the other hand, stabilize the carbanion and thus reduce the nucleophilic reactivity of the ylide. These are so-called stable ylides . 

One of the routes leading to P-stereogenic phosphines is electrophilic substim-tion at the phosphorus atom of secondary phosphines, as a result of asymmetric catalysis in which a catalyst activates a phosphorus nucleophile or a carbon electrophile, creating an asymmetric environment, i.e., creating preference for one of Si or Re face sides at the reactive center [103-113]. Upon reaction with chiral metal complexes, racemic secondary phosphines are converted into diaste-reomeric metal-phosphide complexes A or B, which interconvert rapidly through the inversion at phosphorus. If the equilibrium A B is faster than the reaction of A or B with an electrophile E, then P-stereogenic phosphines 196, in which pyramidal inversion is slow, can be formed enantioselectively. The product ratio in this dynamic kinetic asymmetric transformation depends both on and on the rate constants ks and (Scheme 63). 

Summary Aryl ligands carrying oxygen, phosphorus or sulfur donor atoms in the side chain are introduced at silicon. Here we report on the synthesis of silyl chlorides and silyl triflates. The interaction between the silicon centre and the donor atom are discussed on the basis of NMR and X-ray crystallographic data. In the reaction of bis[2-(methoxymethyl)phenyl]methylsilyl triflate 8 with nucleophiles, reactivity of oxonium as well as of siliconium ions is observed. 

In general, phosphorus compounds prefer to react by electron-pair mechanisms, utilising the nucleophilic reactivity of the lone-pair electrons in the case of trivalent compounds, and the electrophilic-ity of the P atom in pentavalent derivatives. However, some phosphorus reactions proceed by a free radical mechanism (Chapter 13.4). 

By far the main interest in the reaction of halo [ C] acetates with phosphorus nucleophiles is for the preparation of phosphoryl-stabilized carbanions for use in Wittig and related reactions. The presence of the additional electron-withdrawing ester group provides additional stabilization, significantly modifying the reactivity of the ylide species and the stereochemical course of its reactions. The two phosphorus reagents discussed here include the triphenylphosphonium salt type 158. precursors of Wittig methylenetriphe-nylphosphoranes, and the trialkylphosphonoacetate type 159. applied in the Horner-Wadsworth-Emmons family of reactions . ... 

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