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The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a ... With stabilized ylides ...
It is however less reactive than ylides lacking EWGs. For example they usually fail to react with ketones, necessitating the use of the Horner–Wadsworth–Emmons reaction as an alternative. Such stabilized ylides usually give rise to an E-alkene product when they react, rather than the more usual Z-alkene. A "stabilized" Wittig reagent.
It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species. Preparation and use ...
The a-keto stabilized ylides derived from bisphosphines like dppe, dppm, etc., viz., [Ph 2 PCH 2 PPh 2]C(H)C(O)R and [Ph 2 PCH 2 CH 2 PPh 2]C(H)C(O)R (R = Me, Ph or OMe) constitute an important class of hybrid ligands containing both phosphine and ylide functionalities, and can exist in ylidic and enolate forms.
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.
Another method is the Takai olefination which uses iodoform and chromium(II) chloride to make vinyl iodide from aldehyde with high stereoselectivity for E geometry. [27] For high stereoselectivity for Z geometry, Stork-Zhao olefination proceeds by Wittig -like reaction.
The Corey–Fuchs reaction is based on a special case of the Wittig reaction, where two equivalents of triphenylphosphine are used with carbon tetrabromide to produce the triphenylphosphine-dibromomethylene ylide. [2] Step 1 of the Corey-Fuchs reaction, generating the active ylide. This ylide undergoes a Wittig reaction when exposed to an aldehyde.
Georg Wittig (German: [ˈɡeː.ɔʁk ˈvɪ.tɪç] ⓘ; 16 June 1897 – 26 August 1987) was a German chemist who reported a method for synthesis of alkenes from aldehydes and ketones using compounds called phosphonium ylides in the Wittig reaction.