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Wittig reagents are usually described as a combination of two resonance structures: Ph 3 P + CR 2 − ↔ Ph 3 P=CR 2 The former is called the ylide form and the latter is called the phosphorane form, which is the more familiar representation.
A 1,2-Wittig rearrangement is a categorization of chemical reactions in organic chemistry, and consists of a 1,2-rearrangement of an ether with an alkyllithium compound. [1] The reaction is named for Nobel Prize winning chemist Georg Wittig. [2] [3] The intermediate is an alkoxy lithium salt, and the final product an alcohol.
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 ...
Methylenetriphenylphosphorane is prepared from methyltriphenylphosphonium bromide by its deprotonation using a strong base like butyllithium: [1] Ph 3 PCH 3 Br + BuLi → Ph 3 PCH 2 + LiBr + BuH. The phosphorane is generally not isolated, instead it is used in situ. The estimated pK a of this carbon acid is near 15. [2]
The [2,3]-Wittig rearrangement is the transformation of an allylic ether into a homoallylic alcohol via a concerted, pericyclic process. Because the reaction is concerted, it exhibits a high degree of stereocontrol, and can be employed early in a synthetic route to establish stereochemistry.
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.
An example of the aza-Wittig-reaction being utilized in organic synthesis is the synthesis of (–)-benzomalvin A. Two intramolecular aza-Wittig-reactions were used to construct the seven-membered ring and the six-membered ring in the molecule's skeleton. [1] Synthesis of (−)-Benzomalvin A via multiple aza-Wittig-reactions
NaHMDS is used as a strong base in organic synthesis. Typical reactions: To deprotonate ketones and esters to generate enolate derivatives. [3] Generate carbenes by dehydrohalogenation of halocarbons. These carbene reagents add to alkenes to give substituted cyclopropanes and cyclopropenes. [4] To deprotonation of phosphonium salts, generating ...