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Phosphorus ylides are important reagents in organic chemistry, especially in the synthesis of naturally occurring products with biological and pharmacological activities. Much of the interest in the coordination properties of a-keto stabilized phosphorus ylides stems from their coordination versatility due to the presence of different ...
With unstabilised ylides (R 3 = alkyl) this results in -alkene product with moderate to high selectivity. If the reaction is performed in dimethylformamide in the presence of lithium iodide or sodium iodide, the product is almost exclusively the Z-isomer. [16] With stabilized ylides (R 3 = ester or ketone), the (E)-alkene is formed with high ...
Although ylides are "electron-rich", they are susceptible to deprotonation of alkyl substituents. Treatment of Me 3 PCH 2 with butyl lithium affords Me 2 P(CH 2) 2 Li. [3] Having carbanion-like properties, lithiated ylides function as ligands. Thus Me 2 P(CH 2) 2 Li is a potential bidentate ligand. [4]
The dithiophosphine ylides are normally attacked at the phosphorus atom by a nucleophile, for instance the reaction of an alkoxide, phenolate, alcohol or phenol with a 1,3,2,4-dithiadiphosphetane 2,4-disulfide can form a new compound with a phosphorus-oxygen bond.
Crystallographic characterization of the colourless ylide reveals that the phosphorus atom is approximately tetrahedral. The PCH 2 centre is planar and the P=CH 2 distance is 1.661 Å, which is much shorter than the P-Ph distances (1.823 Å). [5] The compound is usually described as a combination of two resonance structures: Ph 3 P + CH 2 − ...
Phosphorus ylides are unsaturated phosphoranes, known as Wittig reagents, e.g. CH 2 P(C 6 H 5) 3. These compounds feature tetrahedral phosphorus(V) and are considered relatives of phosphine oxides. They also are derived from phosphonium salts, but by deprotonation not alkylation.
A variety of organosilver compounds include phosphorus ylides. A simple example is the pentafluorophenylsilver complex of methylenetriphenylphosphorane: [8] AgC 6 F 5 + Ph 3 P=CH 2 → Ph 3 P=CH 2 −AgC 6 F 5. Alkenylsilver compounds are also more stable than their alkylsilver counterparts.
Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction , for instance methylenetriphenylphosphorane or Ph 3 P=CH 2 .