Cyclopropyl phosphonium salt

High yields of dihydrofurans are obtained from the reaction of the cyclopropyl-phosphonium salt (161) with sodium carboxylates.143... 

Other investigators have used a new synthetic route103 in which the spiro[4,5]decane system is formed by condensation of a -dicarbonyl compound [e.g. (221)] with a cyclopropyl phosphonium salt (222).104 The bicyclic keto-ester (223) produced in this way was subsequently converted into ( )-anhydro-/3-rotunol (224), ( )-/3-vetivone (220), ( )-/3-vetispirene (225), ( )-linesol (226), and ( )-a-vetispirene (227) (Scheme 27). 03 An alternative approach to the vetispirane system involves Et[Pg.82]

Schweitzer has synthesized alkylidene cyclopropanes by Wittig reaction with a cyclopropyl phosphonium salt. If, however, the electrophilic character of the cyclopropane is enhanced by a second acceptor group (e.g. CO2R, SR), suitable nucleophiles are able to attack the three-membered ring. The resulting ylid can form hetero- and carbocycles by an intramolecular Wittig reactionas demonstrated in equations 62 and 63. These annulation reactions have been applied to terpene and alkaloid preparations. 

Ylides are intermediates in the synthesis of dihydrothiophens, as shown in Scheme 4, and of a range of heterocycles, e.g. (31), using the cyclopropyl-phosphonium salt (30) as shown in Scheme 5. 

The reaction of cyclopropyl bromide with triphenylphosphine gives the expected phosphonium salt in less than 1 % yield. An alternate route to the salt by the thermal decomposition of 2-oxo-3-tetrahydrofuranyltriphenylphosphonium bromide gives a... 

This is even more so if one compares the relative acidities of the hydrogen atoms in the isopropyl and cyclopropyl substituents of the phosphonium salts 281 and 282. 

The X-ray structure of the pyramidal and thermally very stable ylid 279, however, rigorously excludes that the cyclopropyl hydrogens of the phosphonium salts 281 and 282 might be less acidic than the isopropyl hydrogens because in the latter the ylid is planar, as is the case with cyclopropyl enolates Does R4P" really lead to a violation of the acidity rule ... 

The reaction of cyclopropylidenetriphenylphosphorane (1) with chlorodiphenylphosphane in toluene leads to the phosphonium salt 2, which can be methylated to the bisphosphonium salt 3 and subsequently converted into methyldiphenyl[l-(triphenylphosphonio)cyclopropyl]phos-phonium bis(hexafluorophosphate) (4). ... 

The 13-cw-analogue (56) of (6), was prepared from known [67] phosphonium salt (62) and 4-hydroxy-3-methylbut-3-enolide [77] as indicated in Scheme 1.5. The synthesis of (57), containing a terminal cyclopropyl ring, was effected by Wittig coupling of the ylide from salt (62) with ethyl ( )- 8-formylcyclopropylcarboxylate [78]. 

The pyrrolizidine ring system holds its own fascination for the alkaloid freaks. Two syntheses of the functionalized system, and one which produced the parent skeleton are worthy of note this year. Treatment of carboxyalkyl cyclopropyl triphenyl phosphonium salts (287) with imide anions (286) produced the fused bicycle (288) in good to excellent yields, whereas the functionalized nitrone... 

Cyclization of y-substituted phosphonium " and sulfonium salts by 1,3-elimination followed by proton abstraction affords the corresponding cyclopropyl ylides... 

Double deprotonation of the bisphosphonium salt 4 by triethylethylidenephosphorane does not afford a product with two terminal ylide functions but an unsymmetrical carbodiphos-phorane 5. The formation of cyclopropyl[(methyldiphenylphosphoranylidene)methylene]-diphenylphosphorane (5) occurs via nucleophilic attack of a terminal ylide function at the adjacent phosphonium center in the primary ylide intermediate." ... 

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