Search results
Results From The WOW.Com Content Network
For stabilized Wittig reagents bearing conjugated electron-withdrawing groups, even relatively weak bases like aqueous sodium hydroxide or potassium carbonate can be employed. [Ph 3 PCH 3] + Br −, typical phosphonium salt. The identification of a suitable base is often an important step when optimizing 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 ...
Best practices • Don't enable the "use less secure apps" feature. • Don't reply to any SMS request asking for a verification code. • Don't respond to unsolicited emails or requests to send money.
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.
A phosphonium ylide can be prepared rather straightforwardly. Typically, triphenylphosphine is allowed to react with an alkyl halide in a mechanism analogous to that of an S N 2 reaction. This quaternization forms an alkyltriphenylphosphonium salt, which can be isolated or treated in situ with a strong base (in this case, butyllithium) to form ...
Reduction, iodination, and treatment with triphenylphosphine led to phosphonium salt. Figure 2. Fragments 1, 2, and 3 were reacted with each other to deliver epothilone B in an approach including Wittig reaction, aldol reaction, and Yamaguchi esterification (Figure 3).