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The main limitation of the traditional Wittig reaction is that the reaction proceeds mainly via the erythro betaine intermediate, which leads to the Z-alkene. The erythro betaine can be converted to the threo betaine using phenyllithium at low temperature. [18] This modification affords the E-alkene. The Schlosser variant of the Wittig reaction
Modified Wittig–Claisen tandem reaction is a cascade reaction that combines the Wittig reaction and Claisen rearrangement together. The Wittig reaction generates the allyl vinyl ether intermediate that further participates in a Claisen rearrangement to generate the final γ,δ-unsaturated ketone or aldehyde product (Figure "Modified Wittig ...
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.
In order to obtain the E-alkene, the Schlosser modification of the Wittig reaction can be performed." That agrees with the general description in the "Classical mechanism" section, which accompanies the mechanism leading to 7 (a Z form).
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
In 1958, Leopold Horner published a modified Wittig reaction using phosphonate-stabilized carbanions. [2] [3] William S. Wadsworth and William D. Emmons further defined the reaction. [4] [5] In contrast to phosphonium ylides used in the Wittig reaction, phosphonate-stabilized carbanions are more nucleophilic but less basic. Likewise ...
If Y is nitrogen, the reaction is referred to as the Sommelet–Hauser rearrangement if a quaternary ammonium salt is involved or the aza-Wittig reaction if an alpha-metalated tertiary amine is involved; if Y is oxygen, then it is called a 2,3-Wittig rearrangement (not to be confused with the well-known Wittig reaction, which involves a ...
It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species. It is a highly polar, highly basic species. Preparation and use