Reactions at Phosphorus

Thermolysis of dimethylphosphine oxide at 770K leads to the elimination of water to give 2-phosphapropene (46).27 Cleavage of the normally stable P=0 bond is explained by reference to an energy hypersurface calculated by MNDO methods. This suggests that there is an entropy-favoured dissipation of the activation energy stored in the 

The reactions of allenylphosphine oxides leading to five-membered phosphorus heterocycles have been reviewed.  

Juaristi, L. Valle, C. Mora-Uzeta, B. A. Valenzuela, P. Joseph-Nathan, and M. F. Fredrich, J. Org. Chem., 1982, 47, 5038. 

The chemical and electrochemical oxidations of triphenylphosphine sulphide and phosphorothioates in acetonitrile have been investigated.In both reactions, triphenylphosphine sulphide initially gives a product formulated as a dimeric di-cation (39), but this rapidly decomposes on removal of the solvent or exposure to air. Triphenylphosphine oxide and sulphide form radical anions on treatment with potassium in ether at low temperature or by one-electron reduction at a Hg cathode in DMF. The photo-oxidation (sensitized by polymer-supported Rose Bengal) of triphenylphosphine selenide to the oxide has been shown to be highly solvent-dependent. 

The oxide (40) is thermally stable to at least 140° C, whereas the parent l-phenyl-3-benzophosphepin (41) decomposes to naphthalene and, presumably, phenylphosphinidene at 80 °C.  

Diaryl secondary phosphine oxides have been used to synthesize biphosphine ligands (42) via a substitution-reduction sequence.  

Phosphine oxides (31) bearing two or three pyridyl groups undergo ligand displacement on reaction with organometallic reagents to give substituted 

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The same fluoroalkoxy substituents, however, are able to enhance substitutional reactivity of fluorinated polyphosphazenes by originating methatetical exchange reactions on polymers in the presence of new nucleophiles and under appropriate experimental conditions. Thus, a series of exchange reactions at phosphorus atoms bearing the trifluoroethoxy substituents in PTFEP have been describedbyH.R. Allcock [508] (Fig. 13),Cowie [482,483] (Fig. 14), and Ferrar [509] (Fig. 15), while surface modification of PTFEP films were reported by Allcock [514,515] (Fig. 16 or 17) and by Lora [516] (Fig. 18). 

So far, all evidence is consistent with the interpretation that enzymatic reactions at phosphorus proceed with inversion by an in-line associative mechanism. There has been no need to invoke adjacent mechanisms, metaphosphate intermediates, or pseudorotation. Results are summarized in Table 8.1. 

This section emphasizes work done in the last few years. The reader is referred to other sources for reviews of older work236 or more general discussions of nucleophilic reactions at phosphorus.237"245 More general discussions of enzymic phosphoryl and nucleotidyl transfer are available,246 248 and the role of divalent metal ions has been reviewed.249"251... 

The activating effect of Mg2+ upon the cleavage of the phosphoryl group from the ATP could reflect the enhancement of an SN2 reaction at phosphorus by electron withdrawal and charge neutralization via coordination to the metal (equation 1). Support for an SN2 mechanism comes from a consideration57 of the inhibition by vanadate. Coordination of the transferable phosphoryl group would inhibit the SN1 mechanism. 

Independently on the final result the stereochemical course of SPDE catalyzed hydrolysis of argue against the presumption, that "all enzymatic reactions at phosphorus proceed with inversion and that, therefore, they occur without pseudorotation at phosphorus" /18/. 

We wish to report that on treatment with a solution of sodium hydroxide in aqueous dioxan, (A) was converted by endocyclic P-0 cleavage into (C). Alkylation of (C) with methyl iodide followed by acetylation with acetic anhydride/pyridine resulted in (D), which reacted with a dilute solution of anhydrous hydrogen chloride in methanol to give R-(+)-ethyl 0,S-dimethyl phosphoro-thioate (E). Since both S-alkylation and O-acetylation involve no reaction at phosphorus, and available evidence suggests that under the conditions used acid catalysed P-N cleavage in N,N-dialkyl phosphoramidothioates occurs with inversion (6), the observed sequence (Scheme 2) implies that endocyclic P-0 cleavage occurs with retention of configuration at phosphorus. 

The value of AH is large for reactions at the carbon atom (AH 40 kcal./mole), and hence this determines the reactivity at both saturated and unsaturated carbon atoms. (K 1 and K ->- 1 respectively). The contribution of K A H is much smaller for the reaction at phosphorus, hence the first term determines the relative reactivity in reaction (d), (particularly in the non-polar solvents used in such reactions). These examples are sufficient to illustrate the inadequacy of the SHAB rule when conjugated nucleophiles are considered. 

The phosphorus reagent is first attacked by the OH group (an 5 2 reaction at phosphorus) and the displacement of an oxyanion bonded to phosphorus is now a good reaction because of the anion stabilization by phosphorus. 0 iGy... 

Now the alkoxide anion can attack the positively charged phosphorus atom. This is a good reaction in two ways. First, there is the obvious neutralization of charge and, second, the P-O bond is very strong. This reaction, which we have drawn as an S>j2 reaction at phosphorus, really goes through a pentacovalent intermediate shown to the right, but you will usually see it drawn in a concerted fashion. r -i... 

Step 7 is a nucleophilic acyl substitution reaction at phosphorus, in which ADP reacts with 1,3-diphosphoglycerate, yielding ATP and 3-phosphoglycerate (phosphate transfer). 

Step 10 is a substitution reaction at phosphorus that forms ATP and enolpyruvate, which tautomerizes to pyruvate (phosphate transfer). 

Reactions at Phosphorus Atom with Retention of the Three-Membered Ring... 

Complexes of 1,3-benzazaphosphole systems with other metal carbonyl compounds (Cr, Mo, as well as W) also follow the same pattern, reaction at phosphorus <1998EJI1079>, and exactly comparable behavior was seen in the formation of complexes 61 and 62 from dihydrothiazole-fused and dihydrooxazole-fused 1,3-azaphospholes, respectively <1999JOM(577)337>. 

The reactions of P-halophospha-alkenes with carbenes provide a new route to 1-chloro-lH-phosphirines (181). Such compounds are highly reactive, and a study of nucleophilic displacement reactions at phosphorus has been facilitated by preparation of the related P-W(CO)5 complexes.The first pentacoordinate systems derived from phosphirenes, (182), have been formed in the reactions of P-halo- or P-cyano-phosphirenes with tetrachloro-o-quinone. Evidence has been presented for the rearrangement of P-chlorophosphirenium ions (183) to the vinylphosphenium ions (184)... 

In the next step, alcohol 76 is deprotonated by 75 providing the corresponding alcoholate 77 and intermediate 78. Then, the positively charged phosphorus atom of 78 is attacked by alkoxide 77 in an Sn2 reaction at phosphorus, displacing the stabilized carbamate anion 79. 

Oxygen and phosphorus have a strong affinity as we saw in the conversion of alcohols to bromides with PBt3 and in the Wittig reaction (Chapter 14, p. 000) and so the new alkoxide ion immediately attacks the positively charged phosphorus atom displacing a second nitrogen anion stabilized in the same way as the first. This is an 5 2 reaction at phosphorus. 

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