Darzens reaction
Darzens reaction | |
---|---|
Named after | Auguste Georges Darzens |
Reaction type | Ring forming reaction |
Identifiers | |
Organic Chemistry Portal | darzens-reaction |
RSC ontology ID | RXNO:0000077 |
The Darzens reaction (also known as the Darzens condensation or glycidic ester condensation) is the
Reaction mechanism
The reaction process begins with deprotonation at the
If the starting halide is an α-halo amide, the product is an α,β-epoxy amide.[8] If an α-halo ketone is used, the product is an α,β-epoxy ketone.[2]
Any sufficiently strong base can be used for the initial deprotonation. However, if the starting material is an ester, the
Stereochemistry
Depending on the specific structures involved, the epoxide may exist in
The initial stereochemistry of the reaction sequence is established in the step where the carbanion attacks the carbonyl. Two sp3 (tetrahedral) carbons are created at this stage, which allows two different diastereomeric possibilities of the halohydrin intermediate. The most likely result is due to chemical kinetics: whichever product is easier and faster to form will be the major product of this reaction. The subsequent SN2 reaction step proceeds with stereochemical inversion, so the cis or trans form of the epoxide is controlled by the kinetics of an intermediate step. Alternately, the halohydrin can epimerize due to the basic nature of the reaction conditions prior to the SN2 reaction. In this case, the initially formed diastereomer can convert to a different one. This is an equilibrium process, so the cis or trans form of the epoxide is controlled by chemical thermodynamics—the product resulting from the more stable diastereomer, regardless of which one was the kinetic result.[8]
Alternative reactions
Glycidic esters can also be obtained via
Subsequent reactions
The product of the Darzens reaction can be reacted further to form various types of compounds. Hydrolysis of the ester can lead to decarboxylation, which triggers a rearrangement of the epoxide into a carbonyl (4). Alternately, other epoxide rearrangements can be induced to form other structures.
See also
- Johnson–Corey–Chaykovsky reaction
- Reformatskii reaction
References
- .
- ^ ISBN 978-3-540-30030-4.
- ^ .
- Compt. Rend.(in French). 139: 1214.
- Compt. Rend.(in French). 141: 766.
- Compt. Rend.(in French). 142: 214.
- .
- ^ .