Phosphorus nucleophilic substitution

Phosphorus ylides are prepared from alkyl halides by a two step sequence The first step is a nucleophilic substitution of the 8 2 type by triphenylphosphme on an alkyl halide to give an alkyltriphenylphosphonium salt... 

The second most important nucleophilic substitution in pyridazine A-oxides is the replacement of a nitro group. Nitro groups at the 3-, 4-, 5- and 6-position are easily substituted thermally with a chlorine or bromine atom, using acetyl chloride or hydrobromic acid respectively. Phosphorus oxychloride and benzoyl chloride are used less frequently for this purpose. Nitro groups in nitropyridazine A-oxides are easily replaced by alkoxide. The... 

Kinetic studies have shown that the enolate and phosphorus nucleophiles all react at about the same rate. This suggests that the only step directly involving the nucleophile (step 2 of the propagation sequence) occurs at essentially the diffusion-controlled rate so that there is little selectivity among the individual nucleophiles. The synthetic potential of the reaction lies in the fact that other substituents which activate the halide to substitution are not required in this reaction, in contrast to aromatic nucleophilic substitution which proceeds by an addition-elimination mechanism (see Seetion 10.5). 

The replacement of a heterocyclic hydroxyl group (generally in the 0X0 form, Section II,E, 2,e) with thioxo or chloro groups by phosphorus pentasulfide or phosphorus oxychloride presumably proceeds through nucleophilic substitution (frequently acid-catalyzed, 21 and 86) of thiophosphoryloxy and dichlorophosphoryloxy intermediates. The 4-position in pyrimidine is more reactive than the 2-position and, at low temperature, this type of thionation of pyrimidine-2,4-diones is specific for the 4-position. In as-triazine... 

In the skeleton of many chelating diphosphines, the phosphorus atoms bear two aryl substituents, not least because the traditional route to this class of compounds involves the nucleophilic substitution with alkali metal diarylphosphides of enantiopure ditosylates derived from optically active natural precursors, approach which is inapplicable to the preparation of P-alkylated analogs. The correct orientation of these aryl substituents in the coordination sphere has been identified as a stereo chemically important feature contributing to the recognition ability of the metal complex [11,18-20]. 

Phosphine-borane 63a (75% ee) was obtained by reduction of compound (Sp)-62a using LDBB at -60°C and nucleophilic substitution with iodomethane in 72 % yield. The observed loss of optical purity may be ascribed to stereomutation of the generated tricoordinated phosphorus species. Recrystallization afforded (S)-63a in > 99% ee. On the other hand, severe racemization was observed using the same method with (Rp)-62b. An alternative strategy consisted of deborana-tion of (Rp)-62b using ZSl-methylpyrrolidine, methylation with methyl triflate. 

Diylide 1, by reaction with a phosphorus electrophile, Ph2PCl, lead instantaneously via a nucleophilic substitution and intramolecular prototropy to the formation of functionalized monoylides 10 (Scheme 11). 

Almost no attention has been paid to diphosphine sulfides employed as chiral ligands for palladium-catalysed nucleophilic substitution reactions. In this context, enantiomerically pure diphosphine sulfides derived from 2,2 -biphosphole, which combined axial chirality and phosphorus chiralities, were synthesised, in 2008, by Gouygou et al. through a four-step synthetic sequence. Among various palladium catalytic systems derived from this type of ligands and evaluated for the test reaction, that depicted in Scheme 1.62... 

Nucleophilic substitution reactions involving the replacement of chlorine (or bromine or fluorine) atoms on the phosphorus have been among the most well studied reactions of cyclophosphazenes... 

At the second stage of chlorine substitution in the tetramers there is a greater statistical probability for the incoming nucleophile to attack the phosphorus adjacent to =P(C1)(NHR), viz. P4 or P8, rather than the remote phosphorus, viz. P6 (Fig. 9). However, this statistical effect is countered by the electron releasing effect of the substituent already present on P2, which tends to deactivate P2 as well as P4 and P8 towards further nucleophilic substitution. It is observed that reactive amines such as dimethylamine (94) or ethylamine (95) react with N4P4C18 and... 

Partitioning of carbocations between addition of nucleophiles and deprotonation, 35, 67 Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutational isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudoration in permutational isomerization, 9, 25... 

The phosphine oxide (38) is known to undergo nucleophilic substitution reactions with cleavage of either a phosphorus-phenyl bond, or one of the heterocyclic... 

The mechanism for the reactions with phosphorus halides can be illustrated using phosphorus tribromide. Initial reaction between the alcohol and phosphorus tribromide leads to a trialkyl phosphite ester by successive displacements of bromide. The reaction stops at this stage if it is run in the presence of an amine which neutralizes the hydrogen bromide that is formed.9 If the hydrogen bromide is not neutralized the phosphite ester is protonated and each alkyl group is successively converted to the halide by nucleophilic substitution by bromide ion. The driving force for cleavage of the C—O bond is the... 

Two methods for the preparation of [l,2,3]triazolo[4,5-, pyridazine-4-thione 29 were reported by Bussolari et al. involving nucleophilic substitution of sulfur by displacement of the 4-chloro substituent from 28 and of the oxygen atom of 4-lactam derivative 30 using sodium thiosulfate and phosphorus pentasulfide, respectively (Scheme 18) <1996BMC1725>. 

An alternative approach to selective functionalisation of 75 <2002DEP10115921> involves a first nucleophilic substitution step, followed by reduction of the 7-8 double bond and concomitant removal of the 8-chloride. The reduced species is N-acetylated, and the key intermediate 79 can be functionalized at either of G-2 or of G-6 (Scheme 42). Phosphorus(lll) reduction is then used to remove the remaining chlorine, and the second aromatic ring is reinstated by peroxide oxidation. 

Several enzymic reactions that result in splitting of the pyrophosphate linkage and nucleophilic substitution at the phosphorus atom... 

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