Similarity triphenylphosphine

Similarly, triphenylphosphine dichloride (TPPCI2) can activate aromatic carboxylic acids in pyridine through the formation of acyloxyphosphonium salts (Scheme 2.30).313 A side reaction between tire intermediate acyloxyphosphonium species and a second carboxyl endgroup leading to the formation of anhydrides has been reported.313 This chain-limiting reaction decreases tire molar mass, while the presence of anhydride linkages in tire chains adversely affects the thermal and hydrolytic stability of the final polyester. 

V-Methylpyridinium salts are easily demethylated by triphenylphosphine in DMF, the reaction being accelerated by electron-withdrawing substituents in the pyridine ring. Similarly, triphenylphosphine has been used to debenzylate benzylarsonium salts in the synthesis of asymmetric tertiary arsines. ... 

A soln. of dinitrogen tetroxide in GGI4 added to an ice-salt cooled soln. of triphenyl phosphite in the same solvent until a faint green color appears triphenyl phosphate. Y 84%.—Similarly Triphenylphosphine triphenyl-phosphine oxide. Y 99%. F. phosphates s. J. R. Cox, Jr., and F. H. West-heimer, Am. Soc. 80, 5441 (1958). 

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

A number of reductive procedures have found general applicability. a-Azidoketones may be reduced catalytically to the dihydropyrazines (80OPP265) and a direct conversion of a-azidoketones to pyrazines by treatment with triphenylphosphine in benzene (Scheme 55) has been reported to proceed in moderate to good yields (69LA(727)23l). Similarly, a-nitroketones may be reduced to the a-aminoketones which dimerize spontaneously (69USP3453279). The products from this reaction are pyrazines and piperazines and an intermolecular redox reaction between the initially formed dihydropyrazines may explain their formation. Normally, if the reaction is carried out in aqueous acetic acid the pyrazine predominates, but in less polar solvents over-reduction results in extensive piperazine formation. 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

More recent examples have employed a milder reagent system, triphenyl-phosphine and dibromotetrachloroethane to generate a bromo-oxazoline, which is subsequently dehydrohalogenated. Wipf and Lim utilized their method to transform intermediate 11 into the 2,4-disubstituted system of (+)-Hennoxazole k Subsequently, Morwick and coworkers reported a generalized approach to 2,4-disubstituted oxazoles from amino acids using a similar reagent combination, triphenylphosphine and hexachloroethane. ... 

Similarly the active oxygen of oxaziranes can be transferred to triphenylphosphine with the formation of ]ihosphine oxide and to tertiary amines yielding amine oxides. ... 

In benzene or similar solvents, tris(triphenylphosphine)halogenorhodium(I) complexes, RhX[P(C6H5)3]3, are extremely efficient catalysts for the homogeneous hydrogenation of nonconjugated olefins and acetylenes at ambient temperature and pressures of 1 atmosphere (6). Functional groups (keto-, nitro-, ester, and so on) are not reduced under these conditions. 

A general method for the synthesis of N-unsubstituted aziridine-2-carboxylates involves a triphenylphosphine-mediated reductive cyclization of hydroxy azido esters [17-22]. A recent example involves the treatment of [1-hydroxy-a-azido ester 15 (Scheme 3.6) with PPh3 to give aziridine 16 in 90% yield [19]. a-Hydroxy- 3-azido esters undergo similar reactions to give aziridine-2-carboxylates [20-22],... 

In propylene polymerization by TiCl2 the addition of aluminumorganic compounds results in a fall of the polymerization rale and a concurrent increase of the isotactic fraction content in the polymer (158). A similar effect occurred when triphenylphosphine was added to TiCl2. The content of the isotactic fraction decreased in the series AlEt3 > AlEt2Cl > AlEtCl2. The catalytic activity also decreases in the same row (159). 

Phosphines behave similarly, and compounds of the type R3P and R4P X can be so prepared. The reaction between triphenylphosphine and quaternary salts of nitrogen heterocycles in an aprotic solvent is probably the best way of dealkylating the heterocycles, for example, ... 

Episulfides, which can be generated in situ in various ways, react similarly to give P-amino thiols, and aziridines give 1,2-diamines. Triphenylphosphine similarly reacts with epoxides to give an intermediate that undergoes elimination to give alkenes (see the Wittig reaction, 16-47). 

Geranyl chloride can be prepared from geraniol by the careful use of triphenylphosphine in carbon tetrachloride. Tris(dimethylamino)phosphine reacts with carbon tetrachloride to form the complex (42) which can be used to form the enol esters (43) from acid anhydrides. Similarly, aldehydes form the alkenes (44), and esters or amides of trichloroacetic acid are converted to glycidic esters. ... 

The reaction of triphenylphosphine hydrobromide with phenylpropiolic acid gives a mixture of the )- and (Z)-isomers of 2-carboxy-l-phenyl-vinyltriphenylphosphonium bromide (67), not just the (Z)-isomer as previously reported. ( )-2-Ethoxycarbonyl-l-phenylvinyltriphenylphos-phonium bromide (68) can be prepared in a similar reaction from ethyl phenylpropiolate. 

Monflier et al. (1997) have suggested Pd catalysed hydrocarboxylation of higher alpha olefins in which chemically modified P-cyclodextrin (especially dimethyl P-cyclodextrin) is u.sed in water in preference to a co-solvent like methanol, acetone, acetic acid, acetonitrile, etc. Here, quantitative recycling of the aqueous phase is possible due to easy phase separation without emulsions. A similar strategy has been adopted by Monflier et al. (1998) for biphasic hydrogenations for water-in.soluble aldehydes like undecenal using a water-soluble Ru/triphenylphosphine trisulphonate complex with a. suitably modified p-cyclodextrin. 

Triphenylphosphine dichloride exhibits similar reactivity and can be used to prepare chlorides.18 The most convenient methods for converting alcohols to chlorides are based on in situ generation of chlorophosphonium ions19 by reaction of triphenylphosphine with various chlorine compounds such as carbon tetrachloride20 or hexachloroacetone.21 These reactions involve formation of chlorophosphonium ions. 

Carboxylic acids can be converted to acyl chlorides and bromides by a combination of triphenylphosphine and a halogen source. Triphenylphosphine and carbon tetrachloride convert acids to the corresponding acyl chloride.100 Similarly, carboxylic acids react with the triphenyl phosphine-bromine adduct to give acyl bromides.101 Triphenviphosphine-iV-hromosuccinimide also generates acyl bromide in situ.102 All these reactions involve acyloxyphosphonium ions and are mechanistically analogous to the alcohol-to-halide conversions that are discussed in Section 3.1.2. 

---