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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
A Wittig–Claisen reaction sequence converted the starting material to a 4-pentenal derivative that could serve as a versatile intermediate for the synthesis of various natural products. In this case, the 4-pentenal derivative was further converted to the natural product horsfiline, the active ingredient of a traditional herbal medicine with ...
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.
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).
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 [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.
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 ...
Retrieved from "https://en.wikipedia.org/w/index.php?title=Schlosser_variant&oldid=49613304"This page was last edited on 22 April 2006, at 16:47 (UTC). (UTC).