Cyclopropyltriphenylphosphonium bromide

Cyclopropyltriphenylphosphonium Bromide (5). The lactone salt is pyrolyzed by placing it in a round-bottom flask fitted with an adaptor attached to a vacuum source (aspirator is sufficient). The flask is heated (oil bath) to 180-190° for 48 hours. The residue is a virtual quantitative yield of the tan product, which may be crystallized from ethyl acetate giving cream crystals, mp 189-190°. An alternate setup is convenient if a drying pistol (Abderhalden) is available. The compound is placed in the pistol, which is then evacuated. Decalin (bp approx. 187°) is refluxed over the pistol to provide the heating source. The work-up is the same. 

An electrophilic cyclopropane of a completely different nature consists of carbethoxy-cyclopropyltriphenylphosphonium tetrafluoroborate (475). This compound has been prepared by reaction of cyclopropyltriphenylphosphonium bromide (472) with LDA. Treatment of the resulting ylide (473) with ethyl chloroformate and exchange of the counterion with sodium tetrafluoroborate provides the cyclopropane (equation 160). ... 

The ylid 371 prepared by treating cyclopropyltriphenylphosphonium bromide (with lithium diisopropylamide (LDA) produces a useful synthon on reaction with ethyl chloroformate . The fluoroborate salt (372) was shown to be an excellent reagent for cycloalkenylation of carbonyl compounds. The ylid was used successfully in the total synthesis of Spirovetivanes. ... 

Dehydrohalogenation of 3-(bromopropyl)phosphonium bromides by bases constitutes a convenient route to phosphorylated cyclopropanes. 3-(Bromopropyl)triphenylphosphonium bromide, easily obtained by reaction of 1,3-dibromopropane with triphenylphosphane in xylene,was cyclized with a variety of bases, ineluding sodium hydride,sodium hydroxide, sodium ethoxide, or potassium hydride, to give cyclopropyltriphenylphosphonium bromide. Upon treatment of the latter with an extra equivalent of base, the triphenylcyclopropylidene-/l -phosphane is formed (see Section 5.2.3.7.). 

Apart from these ring closures with y-bromophosphonium salts, phosphonium salts carrying other nucleofuges at the y-position can be utilized in a similar way, albeit in lower yield. 3-(Phenoxypropyl)triphenylphosphonium bromide with butyllithium in tetrahydrofuran was converted into cyclopropyltriphenylphosphonium bromide in 19% yield. ... 

Two methods were employed. Method A was followed when the cyclopropyl group was acyl- and cyano-substituted whereas Method B was used when the cyclopropyl group contained alkoxycarbonyl groups. Method A To a stirred solution of cyclopropyltriphenylphosphonium bromide (3.0 mmol) in HjO (10 mL), kept at 15 C, was added benzene or toluene (40 mL) and 1.8 M aq NaOH (3 mL, 5.4 mmol). The mixture was stirred for 25-60 min, the phases were separated, and the aqueous phase was mixed with 2 M HCl (3 mL) and subsequently extracted twice with benzene or toluene. The combined extracts were dried (NajSO ), the drying agent was filtered, the solvent was distilled under vacuum, and the products were purified by chromatography (silica gel 0.063-0.2 mm, benzene/EtOAc 5 1 or toluene/EtOAc 5 1). The cw-isomer of a cisltrans pair has always the smaller Rj value. 

Most alkylidenecyclopropanes have been prepared by reacting cyclopropylidenetriphenyl-.i -phosphane with aldehydes and ketones. The phosphorus ylide is either prepared by treating cyclopropyltriphenylphosphonium bromide, a stable compound, with base, e.g. phenyl-lithium, potassium er/-butoxide, sodium hydride, or by generating both the phos-phonium salt and the ylide in situ from (3-bromopropyl)triphenylphosphonium bromide employing two equivalents of base. ° The latter method seems to give somewhat better yields, as indicated by the synthesis of l-diphenylmethylene-2-methylcyclopropane (1) from ben-zophenone. ° The yield has also been increased by adding a catalyst. Considerable improvements have in particular been observed by using tris[2-(2-methoxyethoxy)ethyl]amine, a phase-transfer catalyst, e.g. formation of The use of several phosphorus ylides and bases is summarized in Table 25. 

There are various methods for the synthesis of cyclopropyltriphenylphosphonium bromides, the precursor of choice for the preparation of cyclopropylidenetriphenylphosphoranes. Interestingly, attempts to generate the former salt from cyclopropane derivatives, e.g. 1-bromocy-clopropane, have been unrewarding. One exception is the reaction of cyclopropyllithium with tetraphenylphosphonium bromide followed by elimination of benzene from the initial adduct. The intermediate phosphorane 5 was converted into phosphonium salt 13 by reaction with hydrogen bromide. 

Other entries to cyclopropyltriphenylphosphonium bromide (13) involve the thermal decomposition of (tetrahydro-2-oxofuran-3-yl)triphenylphosphonium bromide and the... 

Because of the hygroscopic nature of cyclopropyltriphenylphosphonium bromide (13) use of the tetrafluoroborate salt 16 is recommended. This salt may be prepared in 93% yield by dissolution of the bromide salt and excess sodium tetrafluoroborate in aqueous methanol. Extraction of the aqueous methanolic solution with chloroform, and evaporation of the dried chloroform solution, yields pure tetrafluoroborate salt 16. ... 

A stirred mixture of cyclopropyltriphenylphosphonium bromide (19.25 g, 50.5 mmol) in THF (180 mL) was treated with PhLi (2.32 M in benzene, 21.5 mL, 50 mmol) under an Nj atmosphere. The mixture was stirred for about 45 min then refluxed for 15 min. To the red-brown solution was added dropwise over a 20 min period freshly distilled cyclohexanone (4.91 g, 50 mmol) and stirring with mild heating was continued for 24 h. The light tan mixture was coneentrated and then short-path distilled in vacuo, followed by fractional distillation of the crude distillate yield 2.87 g (47%) > 98% pure (as determined by GC) bp 118-119"C/144Torr. 

Cyclopropyltriphenylphosphonium bromide (8) is converted to cyclopropyldiphenylphosphane (9) by electrochemical reduction or by reaction with lithium aluminum hydride in tetrahydrofuran. ... 

Cyclopropyltriphenylphosphonium bromide is conveniently prepared from 3-bromopropyltriphenylphosphonium bromide (71) by treatment with equimolar sodium ethoxide in absolute ethanol. ... 

Cyclopentylidenecyclopentanol, 294 Cyclopentyllithium, 205 Cyclophanes, 187 Cyclopropanecarbaldehyde, 64 Cyclopropanecarboxylic acid fluoride, 346 Cyclopropanemethanol, 64 Cyclopropanes, 172, 196 Cyclopropanols, 118, 119 Cyclopropanone, 104 Cyclopropenone, 424 Cyclopropylcarbinyl chloride, 463 Cyclopropylidenecycloxhexane, 96 Cyclopropyltriphenylphosphonium bromide, 95-96... 

To an cthanolic solution of 1.38 g (60 mmol Na in 125 ml. of anhyd EtOH) NaOEt is added 27.8 g (60 mmol) of 3-bromopropyltriphenylpliosphonium bromide under nitrogen. The mixture is stirred at 60 C for 20 h, then concentrated and the remaining NaBr removed by filtration. Crystallization of the concentrated filtrate from ethanol-ethyl acetate affords the product as while crystals yield 21.6 g (94%) mp 188 190CC. To a suspension of 0.43 g of NaH (53% suspension in mineral oil) in 20 mL DME are added 3.5 g of cyclopropyltriphenylphosphonium bromide at 20 C under nitrogen followed by a drop of EtOH. This mixture is stirred at 60-70 CC for 4 h after which time 1.8 g (10 mmol) of benzophenone is added. The mixture is stirred for an additional 5 h at the same temperature then poured into ice-water and extracted with hexane. The hexane extract is dried and concentrated and the product purified by distillation yield 1.34 g (75%) bp 140-145rC (4 mm Hg). On storage, the product solidifies mp 64.5-65.5 C (hexane). 

Cyclopropyltriphenylphosphonium bromide was isolated in high yield from the addition of one equivalent of sodium hydroxide to the phosphonium salt (71). 2,2-Diphenylisophosphindolium salts (72) can be formed directly by the addition of o-xylylene dibromide to a mixture of chlorodiphenylphosphine and calcium carbide. ... 

An improved preparation of cyclopropyltriphenylphosphonium bromide by 1,3-elimination from co-bromopropyltriphenylphosphonium bromide with dilute aqueous sodium hydroxide has also been reported. ... 

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