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The mechanism of the Horner-Wadsworth-Emmons reaction. The ratio of alkene isomers 5 and 6 is not dependent upon the stereochemical outcome of the initial carbanion addition and upon the ability of the intermediates to equilibrate. The electron-withdrawing group (EWG) alpha to the phosphonate is necessary for the final elimination to occur.
William D. Emmons (November 18, 1924 – December 8, 2001) was an American chemist and published with William S. Wadsworth a modification to the Wittig-Horner reaction using phosphonate-stabilized carbanions, now called the Horner-Wadsworth-Emmons reaction in his honor.
Leopold Horner (24 August 1911 – 5 October 2005) was a German chemist who published a modified Wittig reaction using phosphonate-stabilized carbanions now called the Horner–Wadsworth–Emmons reaction (HWE reaction) or Horner-Wittig reaction.
Triethyl phosphonoacetate is a reagent for organic synthesis used in the Horner-Wadsworth-Emmons reaction (HWE) or the Horner-Emmons modification. Triethyl phosphonoacetate can be added dropwise to sodium methoxide solution to prepare a phosphonate anion. It has an acidic proton that can easily be abstracted by a weak base.
In the final steps a Horner–Wadsworth–Emmons reaction (methyl 2-(diethy1phosphono)acetate) give acrylate ester 12 as a mixture of cis and trans isomers which could be coached into the right (trans) direction by application of light in a photochemical rearrangement, the ester group was reduced (DIBAL / boron trifluoride) to isostrychnine 13 ...
There is no limit to the number of possible organic reactions and mechanisms. [ 5 ] [ 6 ] However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from ...
Ordinarily, the Horner–Wadsworth–Emmons reaction provides the (E)-enoate (α,β-unsaturated ester), just as the Wittig reaction does. To obtain the (Z)-enolate, the Still-Gennari modification of the Horner-Wadsworth-Emmons reaction can be used.
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