Allylic phosphonium salts

Since electron-donating substituents at the phosphorus atom favor addition reactions over olefination reactions, addition of 9 to aldehydes leads to the exclusive formation of the silyl-pro-tected allylic alcohols 10. No reaction products arising from Wittig alkenylation could be detected. The ylides (R,S)-9 and (S.S)-9 and their enantiomers were prepared from the corresponding optically pure l-[2-(diphenylphosphino)ferrocenyl]-A,A -dimethylethanamine diastereomers 7 via the phosphonium salts 8. 

The ylide obtained from (methyl)triphenylphosphonium bromide reacts with morpholine derivatives 597 to give phosphonium salts 598 which upon treatment with -butyllithium are converted to new ylides 599. In a reaction with aldehydes, ylides 599 form iV-(l,3-disubstituted allyl)-morpholines 602 (Scheme 94) <1996AQ138>. Another less common nucleophile that can be used for substitution of the benzotriazolyl moiety in Af-(a-aminoalkyl)benzotriazoles is an adduct of iV-benzylthiazolium salt to an aldehyde which reacts with compounds 597 to produce adducts 600. Under the reaction conditions, refluxing in acetonitrile, salts 600 decompose to liberate aminoketones 601 <1996H(42)273>. 

Novel alkenylphosphonium salts were subjected to the Wittig reaction (Scheme 12). Allylic deprotonation took place for phosphonium salts possessing such protons, and the olefination proceeded after double bond migration. In cases where such protons were absent, allene formation was observed. 

Allylphosphonium salts are synthesized by substitution of allyl halides with PPh3. The use of allyl alcohol, allyl acetate, or nitropropene with a palladium catalyst has also been reported.19 It is shown in this study that the organophosphorous compounds can be obtained by a palladium-catalyzed addition to an allene. A notable aspect of this method is that it can control the stereochemistry of the phosphonium salt, and that (Z)-allylphosphonium salts have been obtained in pure form for the first time. 

Phosphonium salts, e.g. (124), derived from polynuclear hydrocarbons and used as intermediates in helicine synthesis, have been prepared by the reaction of the appropriate benzylic alcohol with triphenylphosphine hydrobromide.120 Similarly, the salt (125), of value as an intermediate in carotenoid synthesis, has been prepared by the reaction of a precursor allylic alcohol with triphenylphosphine hydrobromide.121 Bromomethyl a-diketones react with triphenylphosphine to form... 

Apart from reactions in which anionic counterparts of phosphonium cations are essentially implicated in a phase-transfer catalysis process (polymer-supported or soluble catalysts see above), some kinds of chemical transformations in which the anion s reactivity is involved have been studied. There are two major advantages, one being experimental and the other the regenerating capability of the reagent, in monomer- or polymer-supported form. The anionic counterparts of phosphonium salts can have an influence on their own stability or structure (the formation of betaines163 and allyl-phosphonium-vinylphosphonium isomerization, for example275,278). 

Alternatively, allyl alcohol could be oxidized to CH2=CHCHO for subsequent reaction with the ylide derived from CH3(CH2)8CH=CHCH2CH=CHCH2CH2OH via its bromide and triphenyl-phosphonium salt. 

Silylamino)phosphines also react with various halides including ethyl bromoacetate, allyl bromide, and chloroformates. The initially-formed phosphonium salts eliminate silyl halides to afford functionalized phosphinimines Me3SiN=P (R)Me2 where R = -CH2C(0)0Et,... 

The mono-substituted butadiene 66 was needed with a trans alkene in the middle. So disconnection 61a looks good and the allyl phosphonium salt 65 did indeed give E-66 though in poor yield. These low molecular weight hydrocarbons are difficult to isolate as they are volatile. 

This reaction based on the petrochemical crude material isobutylene makes the synthetic route to P-ionone (36) substantially shorter and cheaper, especially since the isomeric double bond proves to be advantageous in the subsequent reactions. In addition, i-methylheptenone (37 a) can be converted into methylheptenone (37) by noble metal-catalyzed isomerization. The reaction steps ethynylation (C2 addition), Carroll reaction (C3 addition), ethynylation and partial hydrogenation (C2 addition) lead from methylheptenone (37) via dehydrolinalool (42), pseudoionone (43) and p-ionone (36) to the C15 alcohol p-vinylionol (44). With triphenylphosphine (15), the desired C15 phosphonium salt (13), which is the second important synthetic building block for vitamin A and carotenoids16), is obtained directly from p-vinylionol, by allyl rearrangement. 

Fluorinated bromo or chloro compounds react with triphenylphosphane to fomn phosphonium salts. For example, 3-bromo-3.3-difluoroprop-l-ene (1) can be used to prepare (3,3-difluoro-allyl)triphenylphosphonium bromide (2), a useful reagent for the Wittig reaction. 

Even allyl alcohols such as 7 may be transformed in excellent yield into the corresponding phosphonium salts when triphenylphosphane hydrobromide is used in the reaction." ... 

The order of ease of displacement of groups from the phosphonium salts is allyl, benzyl > phenyl > methyl > 2-phenylethyl > ethyl, higher alkyls. The usefulness of this method for the preparation of various alkyldiphenylphosphine oxides from the available triphenylphosphine is particularly noteworthy. In contrast, the preparative value of this method is diminished in cases where the carbanions correspond ing to the leaving groups on the phosphorus have approximately the same stability. In some cases the reaction is used to prepare the carbon compound (equations 9 to 14). ... 

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