Phosphorus nucleophiles, reactions with

The electrophilic phosphorus atom then undergoes nucleophilic reaction with the alcohol. An intriguing aspect of this reaction is the fate of the proton on the alcohol. There is no strong base present in the reaction mixture. A good possibility is that the carbojgrlate anion removes the proton from the alcohol as it is reacting with the phosphorus. 

No reactions of oxa- or thiadiazines with carbon or phosphorus nucleophiles or with electrophiles at nitrogen were reported during the time period of this review. 

Reaction with Phosphorus Nucleophiles. The ethyleneknine ring can be opened using phosphines (91) or alkaU metal phosphides (92) ... 

Phosphorus nucleophiles have received little attention compared with nitrogen nucleophiles in reactions with fluonnated systems Yields with phosphorus nucleophiles are sometimes low, but interesting materials are obtained [80, 81] (equations 42 and 43). 

When a Br nsted base functions catalytically by sharing an electron pair with a proton, it is acting as a general base catalyst, but when it shares the electron with an atom other than the proton it is (by definition) acting as a nucleophile. This other atom (electrophilic site) is usually carbon, but in organic chemistry it might also be, for example, phosphorus or silicon, whereas in inorganic chemistry it could be the central metal ion in a coordination complex. Here we consider nucleophilic reactions at unsaturated carbon, primarily at carbonyl carbon. Nucleophilic reactions of carboxylic acid derivatives have been well studied. These acyl transfer reactions can be represented by... 

OKO-l,3,7-triazanaphthalene (450) forms acyloxy derivatives in situ with phosphorus oxychloride and pentasulfide which undergo nucleophilic displacement with chloride ion and with a complex sulfide ion, respectively, to form the 4-chloro and 4-thioxo derivatives. The 4-carboxymethylthio compoimd failed to undergo the ring-opening reaction (see below) characteristic of more activated azino- and diazino-pyrimidines, but it did yield about 10% of the 4-0X0 displacement product. 

The nucleophilic properties of phosphorus in phosphaferrocene were demonstrated by reaction with n-butyllithium occurring at the phosphorus atom (81IC3252 820M312). 

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). 

As the phosphonium diylides, lithium phosphonium yldiides, first described by Schlosser and Corey (Ph3P=CR-Li R=H, C3H7) [60-62], have a high nucleophilicity and reactivity. Recently, the a-silylated lithium phosphonium yldiide 20 has been prepared from the stable phosphanyl-(silyl)carbene 19 and alkyl-lithium (Scheme 13). The first crystal X-ray diffraction study of such a reagent was proposed for 20 and its reaction with methyl iodide or phosphorus elec-... 

A. Nucleophilic Reactions of the P=0 Group.—Tris(trifluoromethyl)-phosphine oxide (33) reacts with hexamethyldisiloxane to give a phos-phorane, whose n.m.r. spectrum at — 140 °C shows non-equivalent trifluoromethyl groups. Although this unusual reaction clearly involves nucleophilic attack of the phosphoryl oxygen on silicon at some stage of the reaction, a full study of the mechanism has not been published. Tertiary phosphine oxides can be converted cleanly into dichlorophos-phoranes (34) by treatment with two moles of phosphorus pentachloride. Alkylation of the sodium salt of tetraphenylmethylenediphosphine dioxide (35) with alkyl halides, in dimethyl sulphoxide, has been reported to... 

This reaction may be visualized as proceeding by nucleophilic attack of tervalent phosphorus at the carbonyl group to give an intermediate such as (15). The structure of (16) was deduced from the fact that it was hydrolysed to the known phosphine oxide (17). Methylenephosphoranes (phosphorus ylides) may also be converted into monophosphazenes by reaction with benzonitrile ... 

This section deals with reactions that correspond to Pathway C, defined earlier (p. 64), that lead to formation of alkenes. The reactions discussed include those of phosphorus-stabilized nucleophiles (Wittig and related reactions), a a-silyl (Peterson reaction) and a-sulfonyl (Julia olefination) with aldehydes and ketones. These important rections can be used to convert a carbonyl group to an alkene by reaction with a carbon nucleophile. In each case, the addition step is followed by an elimination. 

Another general method for converting alcohols to halides involves reactions with halides of certain nonmetallic elements. Thionyl chloride, phosphorus trichloride, and phosphorus tribromide are the most common examples of this group of reagents. These reagents are suitable for alcohols that are neither acid sensitive nor prone to structural rearrangement. The reaction of alcohols with thionyl chloride initially results in the formation of a chlorosulfite ester. There are two mechanisms by which the chlorosulfite can be converted to a chloride. In aprotic nucleophilic solvents, such as dioxane, solvent participation can lead to overall retention of configuration.7... 

Sections I and J of Scheme 3.2 show reactions with sulfur and phosphorus nucleophiles. The reaction in Entry 25 is a useful method for introducing thiol groups. The solid thiourea is a convenient source of sulfur. A thiouronium ion is formed and this avoids competition from formation of a dialkyl sulfide. The intermediate is readily hydrolyzed by base. 

The reactions of white phosphorus with tetraalkylammonium cyanides in the presence of a crown ether in acetonitrile give rise to the dicyanophosphide ion, which is found to react with a variety of anionic phosphorus nucleophiles with displacement of cyanide ion to generate new P-P bonded compounds.7... 

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. 

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