Trivalent phosphorus compounds

Trivalent Phosphorus Compounds. Trivalent phosphoms compounds reduce hydroperoxide to alcohols ... 

In contrast to tetravalent phosphorus compounds, trivalent phosphoms atoms, such as in trimethylphosphine, have very small coupling constants, V= 1.8 Hz. Pentavalent phosphorus compounds such as those shown, have 7, % and V coupling constants that vary. Usually, Vhp coupling is 0 Hz. 

In a later paper Speziale and Smith 109) investigated the reaction of trivalent phosphorus compounds with N-monosubstituted a-trichloro-acetamides and a-trichloroacetamide. The products were imidoyl chlorides (129) and dichloroacetonitrile (130), respectively. The intermediacy of enamines (131) was assumed. For the monosubstituted amides the enamine... 

In this paper Speziale and Smith 109) described experiments which led them to modify the mechanism proposed earlier 108) for the reaction of trivalent phosphorus compounds with haloamides. The first step is considered to be attack of the trivalent phosphorus compound on a chlorine atom of the halo amide (132) to produce a resonance-stabilized enolate ion (133). This is reasonable since under conditions where the trichloroamide... 

By application of the Corey-Winter reaction,vicinal diols 1 can be converted into olefins 3. The key step is the cleavage of cyclic thionocarbonates 2 (1,3-dioxolanyl-2-thiones) upon treatment with trivalent phosphorus compounds. The required cyclic thionocarbonate 2 can be prepared from a 1,2-diol 1 and thio-phosgene 4 in the presence of 4-dimethylaminopyridine (DMtVP) ... 

In addition there are certain other methods for the preparation such compounds. Upon heating of the thionocarbonate 2 with a trivalent phosphorus compound e.g. trimethyl phosphite, a -elimination reaction takes place to yield the olefin 3. A nucleophilic addition of the phosphorus to sulfur leads to the zwitterionic species 6, which is likely to react to the phosphorus ylide 7 via cyclization and subsequent desulfurization. An alternative pathway for the formation of 7 via a 2-carbena-l,3-dioxolane 8 has been formulated. From the ylide 7 the olefin 3 is formed stereospecifically by a concerted 1,3-dipolar cycloreversion (see 1,3-dipolar cycloaddition), together with the unstable phosphorus compound 9, which decomposes into carbon dioxide and R3P. The latter is finally obtained as R3PS ... 

A similar situation occurs in trivalent phosphorus compounds, or phosphines. It turns out, though, that inversion at phosphorus is substantially slower than Inversion at nitrogen, so stable chiral phosphines can be isolated. (R)- and (5)-metbylpropylphenylphosphine, for example, are configurationally stable for several hours at 100 °C. We ll see the Importance of phosphine chirality in Section 26.7 in connection with the synthesis of chiral amino adds. 

Photolyses of 3-substituted phenyl azides 53 in hot diethylamine containing pyrene, a singlet sensitizer, furnish mixtures of the 4- and 6-substituted 3ff-azepines 54 and 55. The isomers, however, were not separated and the yields were based on quantitative GC analysis of the reaction mixtures.176 Of mechanistic significance is that the ratios of the isomeric azepines obtained compare favorably with those observed in the deoxygenation of 3-nitroarenes with trivalent phosphorus compounds. 

The deoxygeneration of nitroarenes by trivalent phosphorus compounds in the presence of amines is a useful route to 3/f-azepin-2-amines (cf. compounds 32, Section 3.1.1.4.2.2.). Subsequently, it has been shown, by carrying out the reaction in strongly basic solution, that the process can be extended to the synthesis of 1H-. 3H- and 5//-2-benzazepines from nitronaph-thalenes 43 For example, 1-nitronaphthalenes 3 with dimethyl phosphite in the presence of sodium methoxide and a primary or secondary aliphatic amine, yield the dimethyl 5//-2-ben-zazepin-3-yl phosphonates 4 accompanied, in some cases, by the isomeric 3//-2-bcnzazepin-3-yl phosphonates 5. 

The electrochemical generation and reactivity of phosphoniumyl and related charged radicals have been recently reviewed by Kargin and Bunikova [8]. In 1995, Yasui reviewed the reactivity of trivalent phosphorus compounds in single electron transfer (SET) processes [41] and, in 1990, the EPR features and reactivity of phosphoniumyl radicals were reviewed by Tordo [42]. 

SET reactions involving phosphoniumyl radicals have been developed by Yasui et al. [41,55], particularly for the dediazoniation of arenediazonium salts [56] (Scheme 20) and for the oxidation of trivalent phosphorus compounds [41,57] (Scheme 21). 

The trapping of alkyl, alkoxyl and alkylthiyl radicals by trivalent phosphorus compounds, followed by either a-scission or p-scission of the ensuing phosphoranyl radical, is a powerful tool for preparation of new trivalent or pen-tavalent phosphorus compounds [59]. However, the products of these reactions strongly depend on the BDE of the bonds, which are either formed or cleaved. For example, the addition of phenyl radicals on a three-coordinate phosphorus molecule occurs irreversibly, while that of dimethylaminyl (Me2N ) or methyl radicals is reversible, the amount of subsequent P-scission (formation of compound C) depending on the nature of Z and R (Scheme 25). For tertiary alkyl radicals and stabilized alkyl radicals no addition is observed (Scheme 25) [63]. 

For a number of benzylformic acids we used N-ethylmorpholine as catalyst and D20 as solvent/donor. Once again decarboxylation/deuteration occurs very rapidly and is complete within 4 min. The range of compounds that can be labeled in this manner has been further widened by the recent observation [75-77] that tributylpho-sphine and other trivalent phosphorus compounds (R3P, R= Bu, Ph, Me2N, OEt) catalyze the decarboxylation of a-iminoacids. By using deuterated/tritiated acetic... 

Another example of 6 electron cheletropic reaction is the addition of trivalent phosphorus compounds with the dienes... 

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

An alternative route to heterocycles of type 5 is the reaction of Si Ni with trivalent phosphorus compounds containing P-Cl bonds (16). For example, the reaction of Ph2PCl with Sl,N in a 3 1 molar ratio in CH3CN for 3h at reflux produces an 83% yield of (Ph2PU)2NSCl as moisture-sensitive, pale yellow crystals. 

Compared with peroxysulfur compounds, very few peroxyphosphorus compounds are reported. Phosphorus peroxide derivatives have been postulated as possible intermediates in certain biological transformations, although they have never been isolated in such systems . Monoperoxyphosphonic acid can be prepared in situ and applied for some common oxidation reactions ". Only one example of phosphorus peroxide, i.e. bis(phenylphosphinyl) peroxide, has been studied . It is believed that when trivalent phosphorus compounds are allowed to react with ozone and a source of singlet oxygen, phosphorus ozonides 54 are obtained (equation 89). ... 

Trivalent phosphorus compounds are more readily oxidized than the corresponding nitrogen derivatives on account of their higher nucleophilicity however, the oxidation of such highly reactive substrates by dioxiranes has been sparsely studied. Only about a handful of examples are available in the literature, such that little may be said about the general trends in reactivity and selectivity. 

From the product analyses of PET reactions of trivalent phosphorus compounds such as phosphines and phosphates, it is found that P reacts with nucleophiles such as water and alcohol to yield phosphine oxides and phosphates [92-95]. During a reaction of triphenylphosphines (P(CgH4-X-/ )3 with water to give phosphine oxides 0=P(C6H4-X-/ )3... 

The reagents most frequently used to reduce the A-oxides to the parent heterocycle are trivalent phosphorus compounds. These include the phosphorus trihalides, usually in chloroform or ethyl acetate, triphenylphosphine, and phosphite esters such as triethyl phosphite. Substituents which are easily reduced are not affected, although nitro groups... 

Trifluoromethyl hypofluorite reacts with various sulfides in trichlorofluoromethane at — 78 C forming difluoro- 624 and tctrafluorosulfancs 7,25 while fluorodesulfuration is observed in the reaction of amino acids, e.g. formation of 8.26 In a similar manner, trivalent phosphorus compounds react with trifluoromethyl hypofluorite to give difluoro-substituted derivatives 9.27... 

The most reliable method for generating nitrenes is the thermal or photochemical elimination of nitrogen from azides. An alternative method which is useful for indole and carbazole synthesis is the deoxygenation of aromatic nitro compounds with trivalent phosphorus compounds. Triethyl phosphite is the most commonly used reagent, though more reactive compounds may be useful in special cases (B-79MI30600). 

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