Nucleophilic addition reactions phosphorus nucleophiles

Hexafluoroacetone azine accepts nucleophiles (ROH, RSH, R NH) in positions 1 and 2 to yield hydrazones [27] Phosphites give open-chain products via a skeletal rearrangement [22] Radical addition reactions are also reported [22] Treatment of tnfluoropyruvates with tosylhydrazine and phosphorus oxychlo-ride-pyndme yields tnfluoromethyl-substituted diazo compounds [24] (equation 3)... 

Nucleophilic Addition of Phosphorus Ylides The Wittig Reaction 721... 

Step 4 of Figure 27.7 Phosphorylation and Decarboxylation Three addition reactions are needed to convert mevalonate to isopentenyl diphosphate. Th first two are straightforward phosphorylations that occur by nucleophilic sul stitution reactions on the terminal phosphorus of ATP. Mevalonate is first cor verted to mevalonate 5-phosphate (phosphomevalonate) by reaction wit ATP in a process catalyzed by mevalonate kinase. Mevalonate 5-phosphat then reacts with a second ATP to give mevalonate 5-diphosphate (diphosphc mevalonate). The third reaction results in phosphorylation of the tertiar hydroxyi group, followed by decarboxylation and loss of phosphate ion. 

Highly stabilized phosphorus ylides are prepared from acetylenic esters, a carbon-based nucleophile, and triphenylphosphine in aqueous media.40 In acetone-water (2 1) solvent, the reaction proceeds via the conjugate addition of triphenylphosphine to dialkyl acetylenedicarboxy-lates the resulting vinyl triphenylphosphonium salts undergo Michael addition reaction with a carbon-nucleophile to give the corresponding highly stabilized phosphorus ylides. 

Ah initio calculations to map out the gas-phase activation free energy profiles of the reactions of trimethyl phosphate (TMP) (246) with three nucleophiles, HO, MeO and F have been carried out. The calculations revealed, inter alia, a novel activation free-energy pathway for HO attack on TMP in the gas phase in which initial addition at phosphorus is followed by pseudorotation and subsequent elimination with simultaneous intramolecular proton transfer. Ah initio calculations and continuum dielectric methods have been employed to map out the lowest activation free-energy profiles for the alkaline hydrolysis of a five-membered cyclic phosphate, methyl ethylene phosphate (247), its acyclic analogue, trimethyl phosphate (246), and its six-membered ring counterpart, methyl propylene phosphate (248). The rate-limiting step for the three reactions was found to be hydroxyl ion attack at the phosphorus atom of the triester. ... 

The most interesting properties of phosphoranes, i.e. their role as intermediates or transition states of nucleophilic addition reactions of four-coordinate phosphorus compounds and their intramolecular rearrangements according to BPR or TR, have already been fully considered. The synthetic potential of stable phosphoranes has been reviewed by Burger in great detail (B-79MI11702), and only some special aspects need be mentioned in this chapter. 

Peptides containing a P02 —CH2 linkage can be prepared using a variety of methods, including reactions with nucleophilic phosphorus, such as Arbuzov or conjugate addition reactions, and those in which the phosphorus serves as the electrophile. 

Addition of Hydrogen Halides to an Alkene Section 11.2 Addition of a Nitrogen Nucleophile to an Aldehyde or a Ketone Section 18.8 Figure 18.3 Addition of Phosphorus Ylides to an Aldehyde or a Ketone (The Wittig Reaction) Section 18.7 Figure 18.2... 

The reaction of cyanomethyllithium with 2,4,6-tri-t-butylphenyl-dichlorophosphine enables a one-step preparation of the functionalised phospha-alkene (144). A new route to phospha-alkenes is provided by nucleophilic attack at the vinylic CH2 of the halogenophosphine (145), with displacement of halogen from phosphorus. Thus, with DABCO as nucleophile, the novel system (146) is formed.Treatment of the phosphino-substituted ylides (147) with Lewis acids results in the 2-phosphonio-l-phospha-alkenes (148), reported to be sufficiently stable for X-ray analysis, but also undergoing various addition reactions. 

Nucleophilic Addition of Phosphorus Ylldeti The Wittig Reaction 781... 

A nucleophile adds, forming a trigonal bipyramidal pentacovaient intermediate that then ejects the leaving group in the microscopic reverse of the nucleophilic addition reaction. The pentacovaient intermediate is often short-lived, and this is shown by enclosing it in brackets. The pentacovaient intermediate bonds that are colinear are called axial (or apical) bonds, whereas the three bonds that lie in the plane perpendicular are called equatorial. Three common elements that can react by this pathway are silicon, phosphorus, and sulfur. Hydrolysis of phosphate esters like RNA occurs by this path. 

As shown in Fig. 8, two possibilities are conceivable for the addition step of the imine to the lanthanoid-phosphite complex Ha. To determine whether structure V or VI seems to be the more reasonable in the addition reaction of a dimethyl phosphite with the C=N double bond of cyclic imines, several hydrophos-phonylation experiments using different types of phosphites were carried out in the presence or absence of the Lewis acid boron trifluoride. As it was shown that a high level of Lewis acid activation of the imine is required independently from the nucleophilicity of the phosphorus nucleophile which was used, a transition state of type VI appeared to exist as the dominant transition state structure. 

Nucleophilic Addition of Phosphorus Ylide The Wittig Reaction... 

This reaction was first reported by Pudovik in 1950. It is a base-promoted nucleophilic addition of organophosphorus anion to alkenes or alkynes and is generally known as the Pudovik reaction. Occasionally, it is also referred to as the Pudovik addition. In addition, since Abramov discovered a similar addition reaction of phosphorus compounds to carbonyl compounds at the same time, the addition of organophosphorus compounds to activated unsaturated systems (e.g., alkenes, alkynes, ketones, aldehydes,and... 

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