The Shi epoxidation is a chemical reaction described as an asymmetric epoxidation of olefins with oxone (potassium peroxymonosulfate) and a fructose-derived catalyst (1).
This procedure generates epoxides with high enantiomeric excesses from trans-disubstituted alkenes and trisubstituted alkenes. Cis-disubstituted alkenes and styrenes are asymmetrically epoxidized using a similar catalyst.
An example of an oxirane cascade reaction is given by the synthesis of certain polyether ladder polymers :
This type of ladder compounds are found in marine lifeforms such as red tide. The tri-epoxide is prepared from a triene through asymmetric Shi epoxidation and oxone as primary oxidizing agent. The hydroxyl group in the tri-epoxide is activated as anucleophile by the presence of the base caesium carbonate The bulkytrimethylsilyl groups make such that the polyether is formed with the correctstereochemistry and they are removed in situ by caesium fluoride.