Search results
Results from the WOW.Com Content Network
The Horner–Wadsworth–Emmons (HWE) reaction is a chemical reaction used in organic chemistry of stabilized phosphonate carbanions with aldehydes (or ketones) to produce predominantly E-alkenes. [1] The Horner–Wadsworth–Emmons reaction. In 1958, Leopold Horner published a modified Wittig reaction using phosphonate-stabilized carbanions.
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.
1,2-Oxaphosphetanes are rarely isolated but are important intermediates in the Wittig reaction and related reactions such as the Seyferth–Gilbert homologation and the Horner–Wadsworth–Emmons reaction. [2] Edwin Vedejs's NMR studies first revealed the importance of oxaphosphetanes in the mechanism of the Wittig reaction in the 1970s. [3] [4]
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.
The Horner-Wadsworth-Emmons reaction is a widely used olefination reaction in which a phosphonate-stabilized carbanion reacts with an aldehyde or ketone to form an alkene. In the standard HWE reaction, the phosphonate ester contains alkoxy substituents (typically methoxy or ethoxy), producing an E -alkene as the major product.
In the related Michaelis–Arbuzov reaction the same reactants are known to form a beta-keto phosphonate which is an important reagent in the Horner–Wadsworth–Emmons reaction on the road to alkenes. The Perkow reaction, in this respect is considered a side-reaction.
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 ...
Triethyl phosphite can react with electrophiles in a Michaelis–Arbuzov reaction to produce organophosphonates. For example, the reaction between triethyl phosphite and ethyl bromoacetate produces a phosphonate suitable for use in the Horner–Wadsworth–Emmons reaction.