A phosphorus substituted

Reduction of A -Phosphorus-substituted Imines to A -Phosphorus-substituted Amines... 

The reduction of a-phosphorus-substituted ketones of the general form 7 has also been quite thoroughly researched (Table 7 84i -84s. The product alcohols arc intermediates in Horner -Wittig type alkene syntheses, and can be induced to undergo stcreospecific syn elimination on conversion to the corresponding sodium or potassium (but not lithium) alkoxides. It is often possible to purify the alcohols by crystallization, allowing the synthesis of stereochemically homogeneous alkencs. 

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... 

At this point, it is desirable for us to see just how it was originally proved that a given substitution reaction proceeds with inversion of configuration, even before the mechanism was known. Walden presented a number of examples in which inversion must have taken place. For example, (+)-malic acid could be converted to ( + )-chlorosuccinic acid by thionyl chloride and to (— )-chlorosuccinic acid by phosphorus pentachloride ... 

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). 

The strained hydrocarbon [1,1,1] propellane is of special interest because of the thermodynamic and kinetic ease of addition of free radicals (R ) to it. The resulting R-substituted [ 1.1.1]pent-1-yl radicals (Eq. 3, Scheme 26) have attracted attention because of their highly pyramidal structure and consequent potentially increased reactivity. R-substituted [1.1.1]pent-1-yl radicals have a propensity to bond to three-coordinate phosphorus that is greater than that of a primary alkyl radical and similar to that of phenyl radicals. They can add irreversibly to phosphines or alkylphosphinites to afford new alkylphosphonites or alkylphosphonates via radical chain processes (Scheme 26) [63]. The high propensity of a R-substituted [1.1.1] pent-1-yl radical to react with three-coordinate phosphorus molecules reflects its highly pyramidal structure, which is accompanied by the increased s-character of its SOMO orbital and the strength of the P-C bond in the intermediate phosphoranyl radical. 

The first chapter Heterophenes Carrying Phosphorus Functional Groups as Key Structures presents a detailed description of the recent advances made in this field. The recent studies of all-phosphorus-substituted aromatic compounds have revealed some unique properties of these heterocycles. 

Pyrido[2,l-r ][l,4,2]oxazaphosphorine derivatives 201 were prepared from perhydrooxazolopyridines 200 by treatment with trimethyl phosphite in the presence of SnCU. In this way, the product (R = H) was obtained as a mixture of two diastereomers originating from the different configuration on the phosphorus. In the case of a cyano substituted derivative (R = CN), a third diastereomer was also isolated in a very low yield (Equation 29) <1997T3627, 1997BML2477>. 

The solids considered in this section are phosphorus oxynitrides and nitridooxophosphates. They are pentavalent phosphorus(V) compounds and correspond to a partial substitution of nitrogen, under the nitride form N3, for oxygen 02 within P04 tetrahedra, resulting in the formation of mixed P(0, N)4 tetrahedra. 

The classical Friedel-Crafts approach toward attaching a phosphorus site directly to an aromatic ring would seem a promising route. Phosphorus-centered acid halides would be anticipated to participate in electrophilic aromatic substitution much in the manner of ordinary acyl halides. Early efforts confirmed this concept.48-52 However, difficulties have been encountered in the use of the classical conditions,53 and modifications to the approach have been necessary. 

Similar results for the replacement of halogen on an olefinic linkage by phosphorus have been accomplished using dialkyl phosphites with palladium(O) catalysts.4179 Another reaction involving replacement of a vinylic halide by phosphorus utilizes palladium catalysis with a trimethylsilyl-substituted phosphine (Figure 6.19).80... 

At low concentrations, defect clusters can be arranged at random, mimicking point defects but on a larger scale. This seems to be the case in zinc oxide, ZnO, doped with phosphorus, P. The favored defects appear to be phosphorus substituted for Zn, P n, and vacancies on zinc sites, Vzn. These defects are not isolated but preferentially form clusters consisting of (Pzn + 2V n). 

A variety of optically active 4,4-disubstituted allenecarboxylates 245 were provided by HWE reaction of intermediate disubstituted ketene acetates 244 with homochiral HWE reagents 246 developed by Tanaka and co-workers (Scheme 4.63) [99]. a,a-Di-substituted phenyl or 2,6-di-tert-butyl-4-methylphenyl (BHT) acetates 243 were used for the formation of 245 [100]. Addition of ZnCl2 to a solution of the lithiated phos-phonate may cause binding of the rigidly chelated phosphonate anion by Zn2+, where the axially chiral binaphthyl group dictates the orientation of the approach to the electrophile from the less hindered si phase of the reagent. Similarly, the aryl phosphorus methylphosphonium salt 248 was converted to a titanium ylide, which was condensed with aromatic aldehydes to provide allenes 249 with poor ee (Scheme 4.64) [101]. 

Aqui et al. investigated the cyclization of diethyl A-(3-substituted phe-nyl)aminomethylenemalonates (251) under different cyclization conditions (75JHC557). For cyclization, they applied a 4 7 mixture of concentrated sulfuric acid and acetic anhydride, polyphosphoric acid, polyphosphate (prepared from phosphorus pentoxide and diethyl ether in chloroform), phosphoryl chloride, and Dowtherm A (see Table VI). They found the most effective cyclization conditions were thermal cyclization (heating in Dowtherm A) and polyphosphate. 

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

In contrast to A5-phosphorus-substituted diazo derivatives, which have been known for a long time,22 the synthesis of the first o -diazophosphine was reported as recently as 1985.23 This compound, namely the [bis(diiso-propylamino)phosphino](trimethylsilyl)diazomethane la, was obtained by treatment of the lithium salt of trimethylsilyldiazomethane with 1 equiv of bis(diisopropylamino)chlorophosphine. 

The cavitands are essentially synthesized from their resorc[4]arene precursors which are readily obtained by resorcinol condensation with aldehydes. The main feature comes from the different configurations that are expected for this tetrameric species and the relative thermodynamical stability of each isomer, which has been widely investigated by several authors. In addition, the conformational mobility of the resorc[4]arene molecules will depend on substitution at the upper and lower rims [28, 36, 40, 41]. The first attempt to synthesize a phosphorus bridged cavitand was to treat resorc[4]arene la (1, R=CH3) with phenylphosphonic dichloride or phenylphosphonothioic dichloride. Only inseparable isomer mixtures were obtained and isolation of the desired cavitands was not possible [42]. The first isolated phosphorylated resorcinol-based cavitand was described in 1992 by Markovsky et al., who prepared compound D from la and four equivalents of o-phenylenechlorophos-phate in the presence of triethylamine [43, 44]. For this compound, a tautomeric temperature and solvent dependent equilibrium exists between the spirophosphorane structure and the cyclic phosphate form (Scheme 4). 

Synthesis of triphosphanes by Si—P bond cleavage with PCI3 and further reaction of the triphosphane formed with LiP(SiMe3)2 is described in Section IV. Starting with the lithium derivative of a suitably substituted diphosphane and linking it to the phosphorus atom... 

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