Search results
Results From The WOW.Com Content Network
[Ph 3 PCH 3] + Br −, typical phosphonium salt. The identification of a suitable base is often an important step when optimizing a Wittig reaction. Because phosphonium ylides are seldom isolated, the byproduct(s) generated upon deprotonation essentially plays the role of an additive in a Wittig reaction.
This reagent reacts with a ketone or aldehyde in a Wittig reaction to give an enol ether, which can be converted to the aldehyde by acid-induced hydrolysis. The initial report of the reaction demonstrated its use on the steroid tigogenone. It was later used in the Wender Taxol total synthesis and the Stork quinine total synthesis.
The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent.Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes.
The Michaelis–Arbuzov reaction is initiated with the S N 2 attack of the nucleophilic phosphorus species (1 - A phosphite) with the electrophilic alkyl halide (2) to give a phosphonium salt as an intermediate (3). These intermediates are occasionally stable enough to be isolated, such as for triaryl phosphites which do not react to form the ...
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 methylation of triphenylphosphine is the first step in the preparation of the Wittig reagent. Illustrative phosphorus(V) compounds: the phosphonium ion P(CH 2 OH) 4 +, two resonance structures for the Wittig reagent Ph 3 PCH 2, and pentaphenylphosphorane, a rare pentaorganophophorus compound. The parent phosphorane (σ 5 λ 5) is PH 5 ...
In contrast to phosphonium ylides used in the Wittig reaction, phosphonate-stabilized carbanions are more nucleophilic but less basic. Likewise, phosphonate-stabilized carbanions can be alkylated. Unlike phosphonium ylides, the dialkylphosphate salt byproduct is easily removed by aqueous extraction. Several reviews have been published.
It undergoes a Wittig reaction. [1] ... This makes a phosphonium salt, which is converted to the final product by sodium carbonate in water. [1] Reactions