Triphenylphosphane oxide

An intramolecular aza-Wittig reaction of 1,3-diketones (134) and hydra-zinobis(iminophosphoranes) (133) gives pyrazole (135) on elimination of two equivalents of triphenylphosphane oxide, as shown in Scheme 53 (75CB623). 

As Scheme 120 shows, more benzoxazepines are available by aza-Wittig cyclization of o-acyloxy-2-azidoacetophenone (331). The benzoyloxy derivatives, however, eliminate triphenylphosphane oxide but afford an acyclic product (332) for steric reasons (90S455). 

Oxygen functionalities bonded to a metalloid are replaced by fluorine when reacted with sulfur tetrafluoride. Triphenylphosphane oxide, phenylarsenic acid,219 and triphcnylantimony oxide and its bis(trifluoroacetoxy) derivative222 can be converted by sulfur tetrafluoride into the corresponding organophosphorus, organoarsenic and organoantimony fluorides 16,20 and 21. 

The dioxygen in complexes 3, 8, and 15 can be replaced by carbon monoxide this stabilizes copper in the 1 + oxidation state. Similar reactions occur when complexes [ (tmpa)Cu 2(02)]2+ (3) and [Cu2(XYL—0—)(02)]+ (8) are reacted with triphenylphosphane Cu(I)—PPh3 complexes are formed with the concomitant liberation of dioxygen, as determined quantitatively by manometry. However, [Cu2(N4)(02)]2+ (15) does not react with triphenylphosphane under the same conditions, but triphenylphosphane oxide and [Cu(I)2(N4)(PPh3)2]2+ are formed when the reaction mixture is left to warm to room temperature (Figure 13). 

The catalytically inactive tris(triphenylphosphane) complex E is formed in an equilibrium reaction from the bis(triphenylphosphane) complex F and a third ligand of triphenylphosphane oxide. Loss an acetate ion from complex E does not occur to give tris(triphenylphos-phane)palladium D. Nor does the analogous acetate cleavage from F occur to give bis(tri-... 

Diphenyl tellurium bis[trifluoroacetate] reacted under the same conditions with tetrame-thylurea, sulfoxides, triphenylphosphane oxide and sulfide, triphenylarsane oxide, pyridine 1-oxides, tetramethylpiperidine, benzimidazole, morpholine, and 7V,Ar-diphenylthiourea to give 1 1 complexes as sharp-melting, colorless solids that are soluble in common organic solvents3. 

Phenyl-7-methoxybenzotellurinium perchlorate was oxidized to the 7h,7e -dioxide of the 4-(4//-l-benzotellurin-4-ylidene)-4//-l-bcnzotellurin by triphenylphosphane oxide at 220° or by air in pyridine in the presence of triphenylphosphane1. 

The A -phosphane 1, formed in the reaction of triphenylphosphane with hcxafluoro-propene, reacts further with hcxafluoroacetone in the presence of the fluoride ion. affording triphenylphosphane oxide and perfluoro(2-methylpcnt-2-ene) (2). Formation of fluoro-A -phos-phancs underlies the method for the reduction of perfluoroalkenes which involves the reaction of an alkene with tributylphosphane and subsequent hydrolysis of the A -phosphanc formed. ... 

L = Dihexylsulfoxides trimethylamine l,eu-diaminoalkane(n = 2-4) l,2-bis-(dimethylamino)ethane. tet a lethylpiperid ne pyridine, 4-methyIpyridine 2-methylpyridinc, pyridine 1-oxide 2-, 3-. and 4-methylpyridine 1-oxides triphenylphosphane triphenylphosphane oxide, sulfide, and selenidc " tributylphosphane selenide , tris[4-methoxyphenyl]phosphane selenide, 1,2-bis(diphenylphosphano)ethane f -diselenide, thiourea, letramethylthiourea, dithioxamide dimethylacetamide ... 

The same compounds were obtained when the reactions were performed in degassed solutions in the presence of triphenylphosphane oxide. Attempts to further oxidize these Te, Te-dioxides with hydrogen peroxide, sodium periodate, or 3-chloroperoxybenzoic acid gave a mixture of products but no Te,Te,Te, Te -tetroxides". ... 

This method is unusually mild, using neutral conditions and low temperatures (20 °C and less). It tolerates a number of functional groups in the components (e.g. acetals, esters, alkenes, etc.)- The alcohol, the carboxylic acid and triphenylphosphine are treated dropwise in an inert solvent (dichloromethane, THF, ether) with diethyl azodicarboxylate (DEAD). The ester is formed rapidly. However, tedious chromatography is frequently required to remove the by-products, triphenylphosphane oxide and hydrazo ester. The main value of the reaction lies in the clean inversion of configuration at a secondary carbinol center and in its selectivity towards primary hydroxy groups (vide infra). Inversions are usually performed with benzoic or p-nitrobenzoic acid. The benzoates are purified and saponified with aqueous base to furnish the inverted alcohols in overall yields of ca. 50%. Elimination is the main side reaction. Thus, from (44) 75% of the desired Sn2 product (45) is formed, along with 25% of the elimination product (46) (equation 19). The mechanism of the reaction has been clarified to the point that betaine (47) is the pri-... 

Benzoylation of cyclopropylidenetriphenylphosphorane (1) with benzoyl chloride results in adduct 10 which is hydrolyzed in alkaline medium to cyclopropyl phenyl ketone (11) and triphenylphosphane oxide. ... 

To a suspension of 20.5 mmol of potassium f-butoxide in 20 mL of anhydrous THF, 20 mmol of methyltriphenylphosphoniumbromide are added at 0 °C. After stirring at RT for 15 - 30 min, the suspension is cooled to -78 °C, and 10 mmol of ( S,5R,2-RS)- or (l/ ,55,2-/ 5)-2-hydroxy-l,4,4-trimethyl-3-oxabicyclo[3.2.0]heptane 1.2.8d dissolved in 5 mL of anhydrous THF are added. After 15 min at low temperature, the reaction mixture is stirred at RT overnight. The reaction is quenched with water and most of the THF is evaporated carefully. The residue is extracted with ether and the combined ether phases are dried with MgS04. The solvent is carefully evaporated and triphenylphosphane oxide is separated by flash chromatography with 5% ether/pentane and silica gel. The crude product can be used for next conversion. A further chromatography yields pure product. Yield 78%. 

A solution of 0.87 g (37.5 mmol) of sodium in 30 mL of dry ethanol was dropped quickly under nitrogen into a stirred solution of 14.57 g (37.5 mmol) of benzyltriphenyl-phosphonium chloride in 150 mL of dry ethanol. The reaction mixture became turbid and pale yellow within 10 min at room temperature After having slowly added 12.00 g (37.5 mmol) of 4.14b in 50 mL of absolute ethanol the mixture was stirred for an additional 3 h. It turned colorless but was still turbid. Rota-evaporation afforded a residue which was heated for 10 min under reflux in 200 mL of hexane. Triphenylphosphane oxide was filtered off and the solvent removed from thfe filtrate. The remaining brown oil was purified by column chromatography (10 x 15 cm silica gel, petroleum ether (40-70 °C)/ether 10 1). Principally the stereoisomers could be separated by a second column chromatography. However, the ZJE mixture (Colorless oil, yield 12.40 g (84%)) was used in the following reaction step. 

Another well-known process that utilizes a nucleophilic phosphane is the Mit-sunobu reaction, that is, the reaction between an acidic partner and an alcohol, typically facilitated by an azodicarboxylate and a phosphane. Two options are possible, anchoring of the electrophilic part to the solid support, dealt with in the next section, or anchoring of the nucleophilic phosphane. Georg et al. used polystyrene-bound triphenylphosphane and DEAD (diethyl azodicarboxylate) in their synthesis of aryl ethers [31]. Alcohols were reacted successfully with electron-rich and electron-deficient phenols, giving the desired products in good yield and purity. More recently, Wilhite and coworkers disclosed an efficient protocol for the synthesis of pyridine ethers using ADDP [l,l -(azodicarbonyl)dipiperidine] and polymer-supported triphenylphosphane (Scheme 6.9) [32], Both methods eliminate purification problems caused by triphenylphosphane oxide, but chromatography is still needed. 

The combination of polystyrene-bound triphenylphosphine and carbon tetrachloride has been used for the condensation of N-alkoxycarbonyl a-amino acids and primary amines, including amino acid esters, in the presence of N-methyl-morpholine as base and refluxing dichloromethane as solvent [56]. In this case, supported triphenylphosphane oxide was isolated by filtration after the coupling reaction. The nature of the intermediate involved in the condensation was supposed to be the acid chloride, as these derivatives are found when heating polystyrene-supported dichlorotriphenylphosphorane with carboxylic acids [57, 58], However, evidence supported by infrared spectroscopy suggests the formation of... 

The mechanism of this and similar reactions15 assumes the presence of water which is required for the formation of the triphenylphosphane oxide observed. In fact, in a two-step procedure the phosphazine can be converted during aqueous workup into the hydrazonc 2, which is then cyclized by treatment with potassium /er/-butoxide.12... 

Phenylendiamine reacts with formic acid at 100°C to give benzimidazole in a yield of over 80%. A-Monosubstituted o-phenylenediamines react with other carboxylic acids more slowly, necessitating the addition of hydrochloric or phosphoric acid. A mixture of trifluoromethanesulfonic acid anhydride and triphenylphosphane oxide in dichloromethane is a very efficient dehydrating agent [122]. 

One of the serious drawbacks of the Wittig reaction is the unavoidable production of triphenylphosphane oxide in stoichiometric quantities. Whilst its direct reduction with boron, aluminium or silicon hydrides would be possible, these reagents are too expensive for a viable process. In fact, distilled triphenylphosphane oxide is reacted with phosgene, generated in situ, to give the corresponding dichloride, which is then reduced with metals, like aluminium. [55]... 

The crude product from the Wittig reaction of the Cig-dialdehyde with the Ci5-phosphonium salt contains up to approximately 35% of the (llZ)-isomer, which is isomerised in boiling heptane. Triphenylphosphane oxide is separated off by extraction with a mixture of either DMF and water or alcohol and water. Analytically pure jS-Carotene is then isolated in a yield of 80 %. 

The mechanism is stiU not fiJly understood. Hydrogen peroxide formally transfers oxygen to the nucleophilic phosphorane, which then cleaves off triphenylphosphane oxide to give the aldehyde this finally reacts in a normal Wittig reaction to produce /5-carotene. 

For the concluding Wittig reaction, sodium methoxide in dichloromethane/ methanol is used as the base. After an aqueous work-up, the product is recrystallised by a simultaneous solvent exchange from dichloromethane to methanol. Triphenylphosphane oxide remains thereby in solution. Thermal isomerisation finally gives (all )-astaxanthin in a yield of around 80 % and purity higher than 98 %. 

The chiral La-BINOL-complex is able to catalyze epoxidation of enones using er -butyl hydroperoxide as the oxidant. The addition of triphenylphosphane oxide significantly enhanced the degree of asymmetric induction (up to 96% ee) (118). 

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