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The Shi epoxidation is a chemical reaction described as the asymmetric epoxidation of alkenes with oxone (potassium peroxymonosulfate) and a fructose-derived catalyst (1). This reaction is thought to proceed via a dioxirane intermediate, generated from the catalyst ketone by oxone (potassium peroxymonosulfate).
Asymmetric epoxidation is often feasible. [4] One named reaction is the Jacobsen epoxidation, which uses manganese-salen complex as a chiral catalyst and NaOCl as the oxidant. The Sharpless epoxidation using chiral N-heterocyclic ligands and osmium tetroxide. Instead of asymmetric epoxidation, alkenes are susceptible to asymmetric dihydroxylation.
In the realm of asymmetric methods, both the Sharpless epoxidation [11] and Jacobsen epoxidation [12] surpass asymmetric dioxirane oxidations in enantioselectivity. Additionally, enzymatic epoxidations are more enantioselective than dioxirane-based methods; however, such methods often suffer from operational difficulties and low yields.
The Sharpless epoxidation is viable with a large range of primary and secondary alkenic alcohols. Furthermore, with the exception noted above, a given dialkyl tartrate will preferentially add to the same face independent of the substitution on the alkene.To demonstrate the synthetic utility of the Sharpless epoxidation, the Sharpless group created synthetic intermediates of various natural ...
The asymmetric Darzens reaction between aldehydes and (alpha)-haloesters is an effective method for the synthesis of glycidic esters. [25] Chiral auxiliaries, [26] chiral boron enolates, [27] and asymmetric phase transfer catalysis [28] have been used successfully to effect asymmetric induction in the Darzens reaction. (12)
A breakthrough in the field of organocatalysis came in 1997 when Yian Shi reported the first general, highly enantioselective organocatalytic reaction with the catalytic asymmetric epoxidation of trans-and trisubstituted olefins with chiral dioxiranes. [20] Since that time, several different types of reactions have been developed.
Hydroperoxides are also employed in catalytic enantioselective epoxidations, such as the Sharpless epoxidation and the Jacobsen epoxidation. Together with the Shi epoxidation, these reactions are useful for the enantioselective synthesis of chiral epoxides. Oxaziridine reagents may also be used to generate epoxides from alkenes.
Sharpless asymmetric dihydroxylation; Sharpless epoxidation [34] Sharpless oxyamination or aminohydroxylation; Shenck ene reaction; Shi epoxidation; Shiina esterification; Shiina macrolactonization or Shiina lactonization; Sigmatropic reaction; Simmons–Smith reaction; Simonini reaction; Simonis chromone cyclization; Simons process; Skraup ...