Tris phosphonium ylides

Mechanistic and Theoretical Studies of Phosphonium Ylides and the Wittig Reaction. - The physico-chemical nature of the P-C bond in phosphonium ylides is complex and, despite intensive research over many years, remains the subject of dispute Numerous theoretical studies of this problem have appeared in the scientific literature. A recent contribution to this area by Mitrasinovic uses sharing indices and sharing amplitudes to study P-C bonds in a number of tri-and penta-valent phosphorus species. Sharing indices and amplitudes are quantitative, orbital dependent, measurements of the degree to which an electron, as a wave, is shared between two spatial points in a many electron system. Ylides studied using this method include (1), (2) and (3). ... 

Scheme 5 Wittig reaction of semistabilized tris(2-methoxymethoxyphenyl)phosphonium ylides...

Tris(diethyl)amino]phosphonium 2,2,3,3,4,4-Hexafluorocyclobutane Ylide... 

Tris(diethyl)amino]phosphoniuni 2,2,3,3,4,4-hexafluorocyclobutane ylide (2) is a very hydroscopic solid, which is stable for long periods of time when stored under anhydrous conditions.13 It is unreactive towards most functional groups such as C = C bonds, ketones, aldehydes, and esters but reacts smoothly under neutral conditions with alcohols or carboxylic acids with replacement of the hydroxy group by a fluorine atom.44,45 Other tris(dialkylammo-nium)phosphonium perfluorocyclobutanes have been synthesized however, they are less reactive fluorinating reagents.44,45... 

Triethylammonium 2,2,3,3,4,4-hexafluorocyclobutane ylide (5) is a mild fluorinating agent that has identical properties to [tris(diethyl)amino]phosphonium 2,2.3,3,4,4-hexafluorocyclobutane ylide (2) and gives comparable yields for fluorination of alcohols and carboxylic acids.44... 

The one-electron electrochemical reduction of 1,2-vinylene and buta-l,4-dienylene bisphosphonium salts at a mercury cathode produces an ylide character by the reaction pathway depicted in reactions 11—13. The mechanism is altered when OH is generated in the unbuffered aqueous-organic medium this reaction is depicted as reaction 14. The electrochemical reduction of phosphonium salt in the presence of tri-p-anisylphosphine produces a mixture of the saturated or semi-saturated bisphosphonium salts through either reaction scheme 15 or alternatively 16. 

Two different synthetic strategies were proposed to obtain a variable linker between the phosphoester and the cationic entity. The first was based on the treatment of a fatty dialkylchlorophosphate (obtained from POCl3 and two equivalents of fatty alcohol) with phosphorous and arsenic ylides, which resulted, after acidification, in the phosphonium and arsonium methylenephosphonates. Tri-methylsilyl stabilized ylides... 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

Because the geometry of the 9-double bond was not clear at that time, Corey et al. 75> tried to prepare the (Z)-9-isomer as well as the ( )-9-isomer of leukotriene-A (78 and 86). In the synthesis of the former isomer the tribenzoyl derivative of D-(—)-ribose (79) was converted in 8 stepy into the optically active epoxyaldehyde 71 and the latter to 72. 72 was olefmated with ylide 82, generated by treatment of the corresponding phosphonium mesylate with lithium diisopropylamide in THF/ HMPA75) (Scheme 15). In the first olefination step 72+82- 78, however, similar to the first method, a A9-isomer mixture was formed. The loss of (Z)-selectivity of the Wittig reaction is due to the use of conjugated unsaturated, i.e. moderate ylides of type 82, and had to be expected because of the mechanism of the Wittig reaction (see Sect. 2). 

First, dibromodifluoromethane and hexamethylphosporous amide form a phosphonium salt. The intermediate thus formed reacts with tris(dimethyl-amino)phosphine to give dibromotris(dimethylamino)phosphorane and an ylide with difluoromethylene group attached to phosphorus, difluoro-methylenetris(dimethylamino)phosphorane. 

The phosphorus-stabilized carbanion is an ylide (pronounced ilL-id )—a molecule that bears no overall charge but has a negatively charged carbon atom bonded to a positively charged heteroatom. Phosphorus ylides are prepared from tri-phenylphosphine and alkyl halides in a two-step process. The first step is nucleophilic attack by triphenylphosphine on an unhindered (usually primary) alkyl halide. The product is an alkyltriphenylphosphonium salt. The phosphonium salt is treated with a strong base (usually butyllithium) to abstract a proton from the carbon atom bonded to phosphorus. 

When activated by anionic catalysts [potassium fluoride, cesium fluoride, tctraalkylammonium fluorides, tris(dimethylamino)sulfonium difluorotrimethylsilicate, phosphazenium, hexa-methylpiperidinium and cobaltoccnium fluorides, tetrabuiylammonium difluoro(triphenyl-silyl)silicatc. the complex tetrakis(dimethylamino)ethene/pcrfluoropropene, ammonium (and phosphonium) periluorocyclobuianc ylides], trimethyl(perfluoroalkyl)silanes will generate C-Rp bonds from carbon-halogen bonds. 

Bis(imino) thietanes, 343, 344, are prepared by reaction of isonitriles with iminothiiranes or of ketenimines with p-tolylsulfonyl isothiocyanate. Reaction of phosphonium ketimine ylides, for example, 312, and related compounds with isothiocyanates also gives bis(imino) thietanes, for example, 345. " Treatment of arylsulfonyl isothiocyanates with trimethylacetoisonitrile yields tris(imino)-thietanes, for example, 341. ... 

Triphenyl(trichloromethyl)phosphonium chloride and (dichloromethylene)tri-phenylphosphorane are important intermediates in the reaction system triphenyl-phosphine/carbon tetrachloride. Solutions of (dichloromethylene)triphenyl-phosphorane, which is a convenient Wittig reagent, were first prepared by the addition of dichlorocarbene to triphenylphosphine in chloroform. However, the ylide could not be separated without degradation caused by the reaction medium. 

The diphosphinomethanes (70 R = Me, Ph) react with 1,2-xylylene dibromide to give the bis(phosphonium) salts (71 R = Me, Ph) <820M1266>. By stepwise deprotonation of the salts, the mono-, bis- <81CB1428>, and tris-ylides <820M1266> (72)-(74) have been prepared (74) has been used as a ligand for transition metal ions <820M1266,83AG(E)907>. 

Condensation of the Grignard complex of 58 with triethyl orthoformate (59) gave a 75% yield of distilled hydroxyacetal 60. Partial hydrogenation of 60 to 61, followed by acidic hydrolysis, provided hydroxyaldehyde 62, which was isolated in the (all- -configuration. A Wittig reaction of 62 with the ylide of (a-ethoxycarbonylethyl)-tris(dimethylamino)-phosphonium bromide (63) furnished the hydroxyester 64. Treatment of 64 with ca. 0.5 mol equivalents of PBr3 in ether/hexane at -5°C in the presence of a small amount of pyridine gave an 84% yield of crystalline ester bromide 65, which could be transformed to the phosphonium bromide 55 (yield 93%) by reaction with triphenylphosphine in ethyl acetate. 

Bertrand et al. have introduced a stable acyclic a-aminophosphonium salt. Only basic phosphines, such as tris(dimethylamino)phosphine, allow for the synthesis of stable aminophosphonium salts. The species mentioned gave upon deprotonation with butyllithium the corresponding C-amino phosphorus ylide (Scheme 100/1). In contrast, two cyclic a-amino phosphonium salts were found to be stable despite the presence of weakly basic triarylphosphine moieties. The key intermediates were dicationic aldiminium salts that on treatment with sodium tert-butylate afforded the cyclic a-aminophosphonium salts under discussion (Scheme 100/2 and 3). In Scheme 100/2, the carbenoid intermediate involved is also shown. On treatment with LiHMDS or BuLi, the stable phosphonium salts were converted to the corresponding P-ylides (Scheme 100/2 and 3). In the second example, the cyclic ylide was transformed to a phosphinoarylenamine derivative via a carbenoid intermediate (Scheme 100/3). ... 

A dinuclear Pt complex with chelating tris( -tolyl)phosphine and bridging chloro ligands has been converted into a neutral PPhs-coordinated complex 548 and then into cationic complexes containing phosphonium-substituted enolate ligands (549, Scheme 76). Reaction with phosphorus ylides produces 550 and 551. 

Interest in the synthesis and reactivity of the six-membered, potentially aromatic, phosphinine ring system has also continued, but at a much lower level than in recent years. New synthetic work includes the application of the pyrylium salt route to phosphinine synthesis, this time starting from pyrylium salts bearing chiral substituents to give the related chiral phosphinines," and the development of new routes to the 2-phosphanaphthalene (137)" ° and the phosphinine-2-aldehyde (138). Also reported is an approach to the synthesis of l,2-dihydro-l,4,2-benzo-diazaphosphinines," cationic gold(I) complexes of 2,4,6-tri-t-butyl-l,3,5-triphosphabenzene," and the synthesis of some X -phosphinines from phosphonium-iodonium ylides." " ... 

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