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The alkylphosphonium salt is deprotonated with a strong base such as n-butyllithium: [Ph 3 P + CH 2 R]X − + C 4 H 9 Li → Ph 3 P=CHR + LiX + C 4 H 10. Besides n-butyllithium (n BuLi), other strong bases like sodium and potassium t-butoxide (t BuONa, t BuOK), lithium, sodium and potassium hexamethyldisilazide (LiHMDS, NaHMDS, KHDMS, where HDMS = N(SiMe 3) 2), or sodium hydride (NaH) are also ...
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.
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 − ...
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. [1] [2] [3] Most often, the Wittig reaction is used to introduce a methylene group using ...
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3. [ 1 ] [ 2 ] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent .
The mechanism of the aza-Wittig reaction is analogous to that of the Wittig reaction, with the Wittig reagent replaced by an iminophosphorane. [1] Mechanism of Aza-Wittig-reaction. In some cases, the iminophosphorane is not isolated but generated in situ. In this manifestation, the phosphine, carbonyl, and organic azide are combined
These carbene reagents add to alkenes to give substituted cyclopropanes and cyclopropenes. [4] To deprotonation of phosphonium salts, generating Wittig reagents. NaHMDS deprotonates compounds containing weakly acidic O–H, S–H, and N–H bonds. These include cyanohydrins and thiols. [5]
Unlike the Wittig reaction, the Petasis reagent can react with a wide range of aldehydes, ketones and esters. [4] The Petasis reagent is also very air stable, and is commonly used in solution with toluene or THF. The Tebbe reagent and the Petasis reagent share a similar reaction mechanism.