Phosphonium ion 140

Polyatomic Cations. Polyatomic cations derived by addition of more protons than required to give a neutral unit to polyatomic anions are named by adding the ending -onium to the root of the name of the anion element for example, PH4, phosphonium ion HjU, iodonium ion H3O+, oxonium ion CH3OHJ, methyl oxonium ion. 

The Stability of the resulting neutral species is increased by substituent groups that can help to stabilize the electron-rich carbon. Phosphonium ions with acylmethyl substituents, tor example, are quite acidic. A series of aroylmethyl phosphonium ions have pAT values of 4-7, with the precise value depending on the aryl substituents ... 

Presumably the final step involves alkylation of the (allyloxy)phosphonium ion as shown above. 2-(Allyloxy)benzothiazoles react with y regioselectivity, which is also due to the coordi-native effect of the leaving group towards the organometallic reagents41. 

Direct alkylation of allylic alcohols via the (allyloxy)phosphonium ion intermediate normally proceeds with anti-y selectivity for the Cyclic system, and sy/i-y selectivity for the acyclic system (see Table l)35 36. 

Polysulfides have been prepared with many different types of cations, both monoatomic Hke alkah metal ions and polyatomic Hke ammonium or substituted ammonium or phosphonium ions. In this chapter only those salts will be discussed in detail which contain univalent main-group cations although a large number of transition metal polysulfido complexes have been prepared [7-9]. 

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. 

Among the real chemical species that have been developed along these lines are the cyclopropyl phosphonium ions 1 and 2. 

The phosphonium ion 2 reacts similarly with enolates to give vinyl sulfides. The vinyl sulfide group can then be hydrolyzed to a ketone. The overall transformation corresponds to the reactivity of the dipolar synthon C. 

The selective and facile cleavage of the benzylic ether linkages of 1,2,3 or 4 is accomplished by treatment with iodotrimethylsilane to form the corresponding benzylic iodide. Further addition to these iodide derivatives of 1 affords dendrimers of generation 1 with phosphonium ion sites at the periphery. Such a strategy is conducted up to generation 3 with a phosphine or a phosphonium core (Scheme 3). 

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]. 

The initial observation is that PMMA is essentially completely degraded to monomer by heating to 375°C in a sealed tube while heating a mixture of red phosphorus and PMMA under identical conditions yields a solid, non-deqraded, product as well as a lower yield of monomer. One may observe, by 3C NMR spectroscopy, that the methoxy resonance is greatly decreased in intensity and methyl, methoxy phosphonium ions are observed by 31P NMR. Additional carbonyl resonances are also seen in the carbon spectrum, this correlates with a new carbonyl vibration near 1800 cm 1 in the infrared spectrum and may be assigned to the formation of anhydride. The formation of anhydride was also confirmed by assignment of mass spectra obtained by laser desorption Fourier transform mass spectroscopy, LD-FT-MS. 

Another substituted derivative of BINAP was used by Lemaire et al. [109]. The ammonium salt catalysts (7 and 8, Fig. 41.10) were prepared in situ from the bro-mohydrates and [Ru( /3-2-methylallyl)2(/72-COD)], and immobilized in several ionic liquids. By comparative studies of the hydrogenation of ethyl acetoacetate, the best results were obtained with imidazolium- and pyridinium-containing ionic liquids. No significant ee was observed with the phosphonium salt. This observation was attributed to problems of solubility and to the ability of complexation for the phosphonium ion. From the anionic side, use of the [BF4] anion appeared superior compared to [PF6] and [(CF3S02)2N]A... 

Historically, the concept of EG Bs was developed in relation to electrochemically induced Wittig reactions [45], Co-electrolysis of the phosphonium salt and the carbonyl compound was carried out using the carbonyl compound as the solvent and gave reasonable yields of the alkene [45]. Most of these reactions can be rationalized within Scheme 19, in which the phosphonium ion participates both as the probase (PB) and as the acidic substrate [46]. 

Scheme 19 Wittig reaction with a phosphonium ion as probase and as substrate.

It can be seen from these data that permanganate can easily be transfered from an aqueous phase into methylene chloride solutions. Quaternary phosphonium ions and polyethers (both cyclic and linear) also exhibit large Ke values (30,32). 

Recently, Ohmori and coworkers have used an anodic oxidation reaction to promote the reduction of an acid [34]. In this experiment, the anodic oxidation of triphenyl- or tributylphosphine in the presence of a carboxylic acid led to the formation of an acyl phosphonium ion. The acyl phosphonium ion was then reduced at the cathode to form an ylide which then trapped a second carbonyl... 

Ohmori H, Maki T, Maeda H (1995) Synthetic application of acyl- and alkoxy-phosphonium ions. In Torii, S (ed) Novel trends in electroorganic synthesis, Kodansha, Tokyo, pg 345... 

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. ... 

Phosphines have been advantageously used to convert propagating carbocations to highly stable phosphonium ions that can be studied with 31P NMR [Brzezinska et al., 1977]. 

Lastly, 01ah(1969,12> has proposed the following relationship for tertiary phosphonium ions ... 

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