![synthesis-oxirane-01.gif sintesis williamson del oxirano](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-01.gif)
Mechanism:
![synthesis-oxirane-02.gif Mecanismo síntesis de Williamson](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-02.gif)
The first stage of the mechanism consists of an acid-base balance that depotifies the alcohol, generating a good nucleophile (alkoxide) that cyclizes in the second stage through an intramolecular S N 2 .
Alkene epoxidation: Peracids (MCPBA) react with alkenes to form oxiranes (epoxides).
![synthesis-oxirane-03.gif sintesis-oxirano](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-03.gif)
Mechanism:
![synthesis-oxirane-04.gif sintesis-oxirano](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-04.gif)
Sharples asymmetric epoxidation: Allyl alcohols react enantioselectively with titanium tetraisopropoxide, tert-butylhydroperoxide, and (+) or (-) diethyltartrate to give oxiranes.
![synthesis-oxirane-05.gif sintesis-oxirano-Sharples](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-05.gif)
Darzens synthesis: The reaction starts from halogenated esters in alpha position, which form enolates in a basic medium. Reaction of the enolate ester with aldehydes or ketones, followed by intramolecular S N 2 , produces oxiranes.
![synthesis-oxirane-06.gif sintesis-oxirano-06.gif](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-06.gif)
Mechanism:
![synthesis-oxirane-07.gif sintesis-oxirano-mecanismo Darzens](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-07.gif)
Ester deprotonation.
Nucleophilic attack of the enolate ester on the carbonyl.
Intramolecular nucleophilic substitution that generates oxirane.
Corey synthesis (sulfur ylides): Sulfur ylides react with aldehydes or ketones to form oxiranes.
![oxirane-synthesis-08.gif sintesis-oxirano-Corey](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-08.gif)
Nucleophilic attack of the ylide to the carbonyl.
Cyclization stage taking advantage of the capacity of sulfur as a leaving group.
Sulfur ylide is prepared by methylation of dimethyl sulfide followed by treatment with strong base.
![oxirane-synthesis-09.gif sintesis-oxirano](/images/stories/heterociclos/ciclos-tres/oxirano/sintesis/sintesis-oxirano-09.gif)