Methyltriphenylphosphonium salts

The reaction of bicyclo[3.1.0]hex-2-ene-c/s-6-carboxaldehyde (118) with the ylide produced from a methyltriphenylphosphonium salt and potassium f-ijutoxide in DMSO produced bicyclo[3.2.1]octadiene (119, equation 11.53). There was evidence for an unstable initial product that rearranged with a rate constant of about 10 s in cyclohexane solution at room temperature to produce the final product. What is the structure of the initial product, and why does it react so rapidly to produce 119 ... 

In the absence of the carbonyl or similar stabilizing group, the onium salts are much less acidic. The pATp so of methyltriphenylphosphonium ion is estimated to be 22. Strong bases such as amide ion or the anion of DMSO are required to deprotonate alkylphos-phbnium salts ... 

Furthermore, phosphonium salts have been applied as catalysts in the TMSCN addition to aldehydes [118] and ketones [119]. Methyltriphenylphosphonium iodide [118] was fonnd to be a reasonably active catalyst for the addition of TMSCN to aldehydes at room temperatnre by the gronp of Plumet. In general, the yields varied between 70% and 97% in 24 h, depending on the aldehyde, applied in the reaction (Scheme 46). However, the salt did not support the addition of TMSCN to ketones, with one exception, when the highly reactive cyclobutanone was applied in the reaction [120]. 

The submitter states that the slight excesses of phenyllithium (5 ) and methyltriphenylphosphonium iodide (10%) specified ensure complete corversion of the aldehyde and simplify the purification of the product since the excess phosphonium salt is readily removed during filtration through Florosil. 

The results of the pulse radiolysis in aqueous solution of substituted phosphonium ions have been investigated38 in addition to those of the electrode reduction of benzyl triphenyl-phosphonium ion39 and quaternary phosphonium salts with hydrated electrons40-42. The radiolysis of methyltriphenylphosphonium, dimethyldiphosphonium and trimethyl-phenylphosphonium ions in neutral aqueous solutions leads to phosphoranyl radicals... 

Of a series of quaternary permanganate salts examined as organic oxidants, those of the unsaturated cations benzyltrimethylammonium, benzyltriethylammonium, methyltriphenylphosphonium, ethylenebis(triphenylphosphonium) and hexadecyl-pyridinium all decomposed explosively at —80—90°C, and of tetraphenylarsonium at 120—130°C. The permanganate salts of the saturated cations... 

Two moles of methylenetriphenylphosphorane are reacted with one mole of a dihalogen compound. In the first step methylenetriphenylphosphorane is C-alkylated yielding an to-halophosphonium salt, which subsequently reacts with a second mole of methylenetriphenylphosphorane forming a transylidation equilibrium with methyltriphenylphosphonium halide and an w-halogenated ylide. This compound undergoes intramolecular C-alkylation, in the course of which the resulting exocyclic phosphonium salt... 

Modified Wittig reaction. The reaction of methylenetriphenylphosphorane (prepared in situ from methyltriphenylphosphonium bromide and -butyllithium) with the hydroxy ketone 1 in ether is markedly improved by addition of 3 equiv. of HMPT. As the reaction proceeds, a complex of LiBr and HMPT separates from the ether solution. Probably the Wittig reaction becomes salt free, with enhancement of the rate and increase in yield from 24 to 66%. The product (2) is converted by hydrogenation into er> //rro-3,7-dimethylpentadecane-2-ol, esters of which are sex attractants of pine saw flies. ... 

Allylsilane and Propargylsilane Synthesis. (lodomethyl)-trimethylsilane has been used to prepare aflylsUanes, which are t)q)icafly utilized in Lewis acid or fluoride ion-promoted reactions with carbonyl compounds to provide homoallylic alcohols. Treatment of Mc3SiCH2l with methyltriphenylphosphonium bromide and base produces an intermediate phosphonium salt which can be further utilized to prepare allylsilanes from carbonyl compounds. This procedure has been modified so that this series of transformations can be done as a one-pot procedure (eq 1). ... 

---