Horner-Wadsworth-Emmons reaction
| Horner–Wadsworth–Emmons reaction | |
|---|---|
| Named after |
Leopold Horner William S. Wadsworth William D. Emmons |
| Reaction type | Coupling reaction |
| Identifiers | |
| Organic Chemistry Portal | wittig-horner-reaction |
| RSC ontology ID | RXNO:0000056 |
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.
In 1958, Leopold Horner published a modified Wittig reaction using phosphonate-stabilized carbanions.William S. Wadsworth and William D. Emmons further defined the reaction.
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.
The Horner–Wadsworth–Emmons reaction begins with the deprotonation of the phosphonate to give the phosphonate carbanion 1. Nucleophilic addition of the carbanion onto the aldehyde 2 (or ketone) producing 3a or 3b is the rate-limiting step. If R2 = H, then intermediates 3a and 4a and intermediates 3b and 4b can interconvert with each other. The final elimination of 4a and 4b yield (E)-alkene 5 and (Z)-alkene 6.
The ratio of alkene isomers 5 and 6 is dependent upon the stereochemical outcome of the initial carbanion addition and upon the ability of the intermediates to equilibrate.
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