Wittig Reaction
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The Wittig Olefination Reaction involves
The Wittig Olefination Reaction involves the formation of C–C double bonds, olefins, from carbonyl compounds and phosphorous ylides.
General features:
1. The phosphorous ylides can be prepared from a triaryl- or trialkylphosphine (e.g., triphenylphosphine) and an alkyl halide followed by deprotonation with a suitable base (RLi, NaH, NaOR...).
2. Stabilized ylides have at least one strong electron-withdrawing group (-CO2R), which stabilizes the formal negative charge on the carbon. Ylides that have one aryl or alkenyl substituents are less stabilized. Ylides with only alkyl substituents are the least stable.
3. Many factors determine the stereoselectivity of the reaction. In general terms, stabilized ylides tend to deliver (E)-alkenes, while nonstabilized ylides are prone to give the (Z)-olefins.
4. The ylides are sensitive to moisture and oxygen.
5. Phosphorous ylides are chemoselective, reacting faster with aldehydes than ketones, and remaining intact in the presence of ester or amides.
6. Common solvents in this reaction are diethyl ether, toluene, THF, DME, and MTBE.
Reaction mechanism:
1. Preparation of the phosphonium salt.
2. Formation of the phosphorous ylide by the base.
3. Nucleophilic addition leads to the formation of the betaine.
4. Formation of the oxaphosphetane.
5. Elimination of triphenylphosphine oxide yields the Z-alkene.
Pinterest:
https://www.pinterest.es/pin/67166973...
References:
https://nrochemistry.com/wittig-react...
Seminal publications:
Wittig, G., Geissler, G., Ann. 1953, 580, 44-57.
Wittig, G., Schollkopf, U., Chem. Ber. 1954, 97, 1318-1330. https://doi.org/10.1002/cber.19540870919
Wittig, G., Haag, W. Chem. Ber. 1955, 88, 1654-1666. https://doi.org/10.1002/cber.19550881110
Related videos:
Cope Elimination: Cope Elimination
Hofmann Elimination: Hofmann Elimination
General features:
1. The phosphorous ylides can be prepared from a triaryl- or trialkylphosphine (e.g., triphenylphosphine) and an alkyl halide followed by deprotonation with a suitable base (RLi, NaH, NaOR...).
2. Stabilized ylides have at least one strong electron-withdrawing group (-CO2R), which stabilizes the formal negative charge on the carbon. Ylides that have one aryl or alkenyl substituents are less stabilized. Ylides with only alkyl substituents are the least stable.
3. Many factors determine the stereoselectivity of the reaction. In general terms, stabilized ylides tend to deliver (E)-alkenes, while nonstabilized ylides are prone to give the (Z)-olefins.
4. The ylides are sensitive to moisture and oxygen.
5. Phosphorous ylides are chemoselective, reacting faster with aldehydes than ketones, and remaining intact in the presence of ester or amides.
6. Common solvents in this reaction are diethyl ether, toluene, THF, DME, and MTBE.
Reaction mechanism:
1. Preparation of the phosphonium salt.
2. Formation of the phosphorous ylide by the base.
3. Nucleophilic addition leads to the formation of the betaine.
4. Formation of the oxaphosphetane.
5. Elimination of triphenylphosphine oxide yields the Z-alkene.
Pinterest:
https://www.pinterest.es/pin/67166973...
References:
https://nrochemistry.com/wittig-react...
Seminal publications:
Wittig, G., Geissler, G., Ann. 1953, 580, 44-57.
Wittig, G., Schollkopf, U., Chem. Ber. 1954, 97, 1318-1330. https://doi.org/10.1002/cber.19540870919
Wittig, G., Haag, W. Chem. Ber. 1955, 88, 1654-1666. https://doi.org/10.1002/cber.19550881110
Related videos:
Cope Elimination: Cope Elimination
Hofmann Elimination: Hofmann Elimination
3 سال پیش
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727
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