Nucleophiles carbon-phosphorus bond formation

In addition to the above-mentioned carbon-phosphorus bond formation, the reaction of dienes with nucleophiles is also catalyzed by a palladium complex. 

While technically not "organometallics," enamines are reagents that can provide nucleophilic carbon for new bond formation. Two groups of researchers have reported on the use of such reagents for the formation of new carbon-phosphorus bonds through displacement of chloride from phosphorus.72 73 For example, displacement of bromide from phosphorus tribromide has been used for the introduction of a new thiophosphoryl functionality adjacent to an original carbonyl group (Equation 4.28).72 This approach provides a facile access to (3-ketophosphonates. 

Instability in the supposedly stable phosphorus-carbon bond displays itself not only in unfortunate ways, leading as it does to side reactions and the formation, in synthesis, of unwanted by-products, but also in a constructive manner, forming the basis of reaction sequences of outstanding value in synthesis, as for example in alkene-forming reactions. Instability is an inherent property of (a-hydroxyalkyl)phosphonic acids which manifests itself in phosphorus-carbon bond cleavage as a result of the action of heat or of alkali, and which can lead either to dissociation into precursors or to rearrangement to phosphates (a-oxoalkyl)phosphonic derivatives are susceptible to attack by nucleophiles, a process which also results in carbon-phosphorus bond fission. 

Reactions of vinylphosphonates j2 with an equimolar amount of lithium dialkylcuprates J result in the formation of complexes 3 containing two different organic ligands. These complexes react with electrophiles in various ways. In each of them a diverse ligand plays the role of a nucleophile. Hydrolysis of 3 or alkylation with alkyl halides affords the corresponding phosphonates k and 5 comprising extended saturated carbon chains bonded to phosphorus. However, in a number of reactions with aldehydes, the complexes 3 were found to undergo almost completely selective transformation into carbinols 6... 

By far the most important type of reaction displayed by halophosphines is nucleophilic substitution. This is pivotal to the preparation of many other three-coordinate compounds containing either solely P—C, P—O, P—N bonds, or mixed combinations. These reactions are often exothermic and frequently carried out at low temperatures. For the synthesis of phosphorus(III) compounds containing a P—O or P—N bond it is often necessary to add a base (triethylamine or pyridine are frequently used) to capture the hydrogen halide eliminated from these condensation reactions. In the case of P—C bond formation, a variety of routes are possible using various carbon-derived nucleophiles. 

A representation of some nucleophilic displacement reactions utilizing bromoethane (ethyl bromide, CH3CH2Br) as a prototypical primary alkyl substrate upon which the various nucleophiles act. The display of synthetic versatility in the Sn2 reaction producing the many varieties of compounds illustrates carbon-oxygen, carbon-sulfur, carbon-nitrogen, carbon-phosphorus, and carbon-carbon bond formation and should not be taken to exclude other possibilities. The details of the conditions might be specified as in Table 7.4 for each case but are omitted here for brevity. 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

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