The reaction process begins with deprotonation at the
halogenated position. If the starting halide is an α-halo
amide, the product is an α,β-epoxy amide. If an α-halo ketone is used, the product is an α,β-epoxy ketone. Any sufficiently strong base can be used for the initial deprotonation. However, if the starting material is an ester, the
alkoxide corresponding to the ester side-chain is commonly chosen in order to prevent complications due to potential
acyl exchange
side reactions.
Stereochemistry Depending on the specific structures involved, the epoxide may exist in
cis and trans forms. A specific reaction may give only
cis, only
trans, or a mixture of the two. The specific
stereochemical outcome of the reaction is affected by several aspects of the intermediate steps in the sequence. 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.
Alternative reactions Glycidic esters can also be obtained via
nucleophilic epoxidation of an
α,β-unsaturated ester, but that approach requires synthesis of the alkene substrate first whereas the Darzens condensation allows formation of the carbon–carbon connectivity and epoxide ring in a single reaction. == Subsequent reactions ==