Phosphorus-Containing Nucleophiles

Reactions of several phosphorus-containing nucleophiles with acetylenic esters are reported in the literature. Tertiary phosphines react with acetylenic esters, yielding a variety of products, depending on the reaction conditions. The reaction of triphenylphosphine with DMAD, for example, in ether around —50° gives an unstable 1 2 adduct, formulated as cyclopropenylmethylidenephosphorane (425), which on 

Wilson and Tebby have studied the reaction of triphenylphosphine with different acetylenic esters in alcohol medium and have shown that /3-alkoxyvinylphosphonium ylides and vinyl ethers are formed through the alcoholysis of vinyl phosphonium intermediates. Thus, triphenylphosphine reacts with DMAD in methanol to give the phosphorane (432) [Eq. (62)]. The reaction with propiolic esters, on the 

The reaction of triethylphosphine with DMAD gives the phosphole (446), which was earlier formulated as (445) [Eq. (63)].  

The reaction of tetraphenylbisphosphine (447) with excess of DMAD gives the phosphine oxide 449, presumably formed through the intermediate phosphorane (448) [Eq. (64)]. On the other hand, the reac- 

Diphenylphosphine oxide reacts with diethyl acetylenedicarboxylate to give a 2 1 adduct (460), and it has been suggested that in this reaction the phosphine oxide reacts in the tervalent form [Eq. (68)]. On the 

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Mirskova, A.N., Seredkina, S.G., Kalikhman, I.D., and Voronkov, M.G., Synthesis and reactions of organyl chloroethynyl sulfides with phosphorus-containing nucleophiles, Izv. Akad. Nauk SSSR, Ser. Khim., 2818, 1985 Bull. Acad. Sci. USSR. Div. Chem. Sci. (Engl. Transl.), 2614, 1985. 

Furin, G.G., Phosphorus-containing nucleophiles in reactions with polyfluorinated organic compounds, Usp. Khim., 62, 201, 1993 Russ. Chem. Rev., 62, 243, 1993. 

The reactivity of phosphorus-containing nucleophiles towcu-ds polyfluoro organic... 

Peroxomonophosphoric acid (PMPA) oxidizes dimethyl sulphoxide in high yield in water and aqueous ethanol . In neutral solution the reaction mechanism was thought to be very complex but actually occurs by two different mechanisms that are very similar to those for sulphoxide oxidation by peracids in acidic and basic media. In an alkaline medium the mechanism involves nucleophilic attack by a phosphorus-containing species (probably POs ) on the sulphur atom of the sulphoxide, followed by O—O bond scission yielding the sulphone (equation 24). In acidic solution, on the other hand, the sulphoxide is the nucleophilic species as detailed in equation (25). It should be noted however that there is some evidence that these mechanisms are oversimplified since there are other nucleophilic species (such as H2P05 and HPO ") present in aqueous solutions of PMPA over a wide pH range . 

In spite of the general ambiphilicity of phosphonio-substituted phosphoHde derivatives, the aromaticity of the phosphoHde ring [10, 11] tends to reduce their electrophilicity while the intramolecular compensation of the negative charge by the phosphonio-substituents lowers at the same time their nucle-ophilicity [15, 16]. Bis-phosphonio-benzophospholides and -1,2,4-diaza-phospholides are therefore less reactive towards electrophiles and nucleophiles than other types of phosphorus containing multiple-bond systems and lack the notorious hydrolytic instabihty of many of these species [15, 16, 24]. Reactions are observed, however, with sufficiently strong electrophiles such as triflic acid or methyl triflate, or nucleophiles such as OH" or lithium alkyls, respectively. 

By contrast, the use of phosphines as catalysts is a more recent phenomenon and the development of chiral phosphines has been less well explored, possibly also because of synthetic difficulties associated with developing chiral nucleophilic phosphorus-containing scaffolds. 

This enzyme system catalyzes the oxidation of various nitrogen-, sulfur -, and phosphorus-containing compounds, which tend to be nucleophilic, although compounds with an anionic group are not substrates. For example, the N-oxidation of trimethylamine (Fig. 4.19) is catalyzed by this enzyme, but also the hydroxylation of secondary amines, imines, and arylamines and the oxidation of hydroxylamines and hydrazines ... 

SCHEME 5.4 Cyclization of polyacrylonitrile initiated by a nucleophilic phosphorus-containing species. 

Flavin-containing monoxygenase oxidizes a variety of xenobiotics that contain nucleophilic nitrogen, sulfur, and phosphorus atoms. An early assay for this enzyme was published by Cashman and Proudfoot (1988). A more recent assay, developed by Kawaji et al. (1993) uses benzydamine, a nonsteroidal anti-inflammatory drug, as a substrate. The benzydamine N-oxide formed is fluorescent. 

In addition, there may be an equilibrium in ring-opening polymerizations between onium ions and covalent species. This equilibrium has been observed in the polymerizations of cyclic ethers [29], oxazolines [68], and phosphorus-containing monomers [69], The position of the equilibrium and its dynamics depend on the relative nucleophilicities of the monomer and the counteranion, as well as on the nucleofugacity ot the leaving group. 

Substrates usefully employed in Mannich reactions are, in general, XH compounds having nucleophilic properties, with X being equal to C, N, or other heteroatoms (Fig. 4). In particular, CH compounds are suitably activated saturated and unsaturated derivatives, and NH substrates may be amines, amides, hetcrocyclcs, etc. Out of OH sub-stratcs, alcohols are mainly able to give stable Mannich products. Sulfur- and phosphorus-containing substrates are XH derivatives having the H atom bonded to the hetcroatom in the lower oxidation state, i.e., thiols, sulfinic acids, and, respectively, phosphine and phosphorous acid derivatives. As and Se compounds have also been successfully used. All these substrates are listed in more detail in Sec. D of this chapter. 

Other trivalent phosphoms-containing nucleophiles, such as trialkyl phosphites [P(OR3)j, dialkyl alkylphosphonites [R P(OR)2], or alkyl dialkylphosphinites [R 2P(OR)J, can convert primary carbohydrate halides 177, 178, 179 to corresponding phosphorus derivatives 180, 181, 182 via the Michaelis-Arbusov reaction (O Scheme 78) [ 122,123]. 

Interest in the Staudinger reaction of phosphines with azides, and the Mit-sunobu reaction involving nucleophilic attack by phosphorus at nitrogen in esters of diazodicarboxylic acids, has continued. Systems of the type (205) have been obtained from the reactions of secondary arylphosphines with azides. Treatment of these with butyllithium results in deprotonation to form the diaminophosphonium diazaylides (206). Phosphazenes have been prepared from azido-quinolines and -triazines, and also from diazoketones " and polycyanocyclopropanes. The Staudinger reaction has been employed in the synthesis of phosphorus-containing dendrimers, and in new approaches to amide and peptide synthesis. The reaction has also been used in a high-... 

Rings containing Nitrogen. - The reactions of aziridines with alkylidene-phosphoranes and with phosphorus(III) nucleophiles and the reactions of... 

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