Phosphonium ions based

A variety of reagents can function as the electrophile E+ in the general mechanism. The most useful synthetic procedures for preparation of halides are based on the halogens, positive halogens sources, and diethyl azodicarboxylate. A 1 1 adduct formed from triphenylphosphine and bromine converts alcohols to bromides.15 The alcohol displaces bromide ion from the pentavalent adduct, giving an alkoxyphosphonium intermediate. The phosphonium ion intermediate then undergoes nucleophilic attack by bromide ion, forming triphenylphosphine oxide. 

P-gp substrates are in general either neutral or cationic at physiological pH (weak bases). Weak bases can cross the lipid membrane in the uncharged form and reprotonate in the negatively charged cytosolic leaflet of the membrane. With a few exceptions (e.g., the tetraphenyl phosphonium ion, which can reach the cytosolic membrane leaflet due to charge delocalization [70]), permanently charged cations do not cross the cell membrane and therefore cannot interact with P-gp in intact cells. They can, however, insert into the cytosolic leaflet in inside-out cellular vesicles and are then transported by P-gp [42, 71]. 

Results of a study of polar, steric and structural influences on the kinetics of proton transfer (ylide formation) from phosphonium ions to electrogenerated bases have been interpreted with caution. ... 

Crown ether, cryptand, and poly(ethylene glycol) catalysts are more stable in base than the quaternary ammonium and phosphonium ions. Only the polyethylene glycols) are likely to meet industrial requirements for low cost, although a number of more efficient, lower cost crown ether syntheses have appeared recently, such as those of sila-crowns 64 bound to silica1B9). 

The membrane potential increased with increasing hydrocarbon chain length. Figure 7 shows the transport rate constants of various phosphonium ions as a function of the membrane potential. The selectivity coefficient of tpp+ has also been determined using a nitrobenzene—based membrane electrode45 a value of log KPot = 8.75 was reported, which is lower than that obtained with the arsenic analogue. 

Electrochemical generation of strong base has been applied in an interesting modification of the Wittig reaction 161 A solution of azobenzene, benzaldehyde, benzyltriphenylphosphonium bromide, and lithium chloride in dimethylformamide was electrolyzed at a potential where only the easily reducible azobenzene was electroactive. The phosphonium ion then acts as a proton source, giving the ylide as an intermediate. Under these conditions a 98 % yield of a mixture of cis- and trans-stilbene was obtained, presumably via the following reactions ... 

As depicted in equation (20), the addition of a phase transfer agent, (eg. quaternary ammonium or phosphonium ions), brings permanganate into solution in nonaqueous solvents. Once solubilized, it reacts with alkenes to produce an intermediate that has been characterized by Ogino et al. as a cyclic manganate(V) diester (9), that can be decomposed by acidic solutions to yield aldehydes or by mild base to give the cone KNiding a-diol, as in Scheme 1. 

Various fluorinated aromatic nucleobases have been synthesised for PNA. As is found with similar fluorinated aromatic bases in DNA (section 1.3.3), they behave as universal bases with complementary DNA. PNA with a terminal 9-aminoacridine has been prepared to examine binding of monovalent ions. A Tio PNA oligomer was found to be sensitive to increasing the concentration of K(f) ions, but the presence of the terminal acridine significantly reduced the sensitivity. The incorporation of naphthalene diimide at the N-terminus of PNA stabilises DNA-PNA duplexes, whilst the bis-functionalised PNA (31) not only stabilises the duplex with DNA but also can be used to photocrosslink to DNA. The presence of the phosphonium ion in (31) aids mitochondrial location of the PNA. 

The Merrifield resin-based polyammonium ion species are closely related to a series of polyphosphonium ion materials reported to be biocidal toward several strains of bacteria.49 50 These materials were not elaborated about the phosphonium ion sites, but rather were produced by the polymerizing or copolymerizing p-vinylbenzyltributylphosphonium salts. The antibacterial activity of such materials, resulting from binding... 

Organophosphonium salts are a general class of compounds which are difficult to analyse via conventional EI-MS Thus several reports have appeared in the literature which describe the use of alternative ionization methods to analyse this important class of compounds " Early studies, which centered around the use of field desorption (FD), demonstrated that the intact phosphonium ion is often the most abundant ion. A comparison was made between the use of FD and FAB as ionization methods for the analysis of the diphosphonium salt FD produces high abundances of the intact phosphonium ions [M - Br ] and [M - 2Br ], whereas these ions are only minor peaks in the FAB mass spectrum using glycerol as the matrix. Instead, the fragment ion 35 is the base peak in the FAB spectrum. 

Trimethylphosphine (TMP) and dimethylphosphine (DMP) were protonated by acid surface sites to give the corresponding phosphonium ions, which were observed, for instance, by Bein et al. [747], when they contacted the phosphine vapors with the acid H-Y zeolite. DMP is the weaker base and exhibited some advantages ... 

Phase transfer catalyzed reactions in which ylides are formed from allylic and ben-zylic phosphonium ions on cross-linked polystyrenes in heterogeneous mixtures, such as aqueous NaOH and dichloromethane or solid potassium carbonate and THF, are particularly easy to perform. Ketones fail to react under phase transfer catalysis conditions. A phase transfer catalyst is not needed with soluble phosphonium ion polymers. The cations of the successful catalysts, cetyltrimethylammonium bromide and tetra-n-butylammonium iodide, are excluded from the cross-linked phosphonium ion polymers by electrostatic repulsion. Their catalytic action must involve transfer of hydroxide ion to the polymer surface rather than transport of the anionic base into the polymer. Dicyclohexyl-18-crown-6 ether was used as the catalyst for ylide formation with solid potassium carbonate in refluxing THF. Potassium carbonate is insoluble in THF. Earlier work on other solid-solid-liquid phase transfer catalyzed reactions indicated that a trace of water in the THF is necessary (40). so the active base for ylide formation is likely hydrated, even though no water is included deliberately in the reaction mixture. 

In addition, enantiomers based on the element phosphorous are also possible for example phosphine, phosphine oxide, phosphinates and the phosphonium ion. 

Another highly selective polyaddition is based on the reaction between phenols and oxazolines, which was applied for the synthesis of hb poly(etheramide)s (3-10). The AB2-monomer 2-(3,5-dihydroxyphenyl)-l,3-oxazoline was polymerized thermally at 190 °C in N-methylcaprolactam solution and randomly branched products with a DB of 50% were obtained.Kakodawa et al. used monomer 3-14, namely 2,2-bis(hydroxymethyl) propyl acrylate, for the synthesis of poly(ether ester)s via triphenylphosphine catalysis. The polymers had only low molecular weight, but as they contain phosphonium ions they can be applied in flame-retardant coatings, which can be cured by UV. These materials can also be synthesized via an A2+Bs-approach [vide infra) of tri(acryloy-loxyethyl) phosphate in the presence of piperidine." ... 

Thephosphoms ylide starting material is synthesized from the corresponding phosphonium ion, which is deprotonated by a strong base such as n-butyllithium ... 

Ionic Liquids with different unsymmetrical cations. The most important classes are Ionic Liquids having as cation either imidazolium derivatives or quaternary ammonium ions pyrrolidimium-, piperidimium-, or morpholinium-based derivatives or quaternary phosphonium ions [23]. As counterions, simple halogenides are possible or more hydrophobic ions such as PFg or bis ((trifluoromethyl) sulfonyl) amide (N(S02CF3)2). ... 

The phosphonium ion contains acidic hydrogens that can be removed by strong bases such as alkyllithium reagents. The product is an ylide (pronounced ill-id), a compound containing opposite charges on adjacent atoms (Fig. 16.81). 

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