How does Sharpless epoxidation work?

The Sharpless epoxidation reaction is an enantioselective chemical reaction to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols. The oxidizing agent is tert-butyl hydroperoxide. The method relies on a catalyst formed from titanium tetra(isopropoxide) and diethyl tartrate.

How many enantiomers are produced during Sharpless epoxidation?

two enantiomers
10.2. 1.3 Kinetic resolution. If a racemic secondary allylic alcohol is subjected to Sharpless asymmetric epoxidation, one of the two enantiomers of the allylic alcohol usually reacts much faster than the other.

Which component is required for Sharpless asymmetric epoxidation?

As discussed, there are four main elements required for Sharpless epoxidation: the allyl alcohol, t- butylhydroperoxide (TBHP), the transition metal catalyst Ti(OiPr)4 and the chiral ligand (dialkyltartrate).

Why is the Sharpless epoxidation important?

The Sharpless Epoxidation allows the enantioselective epoxidation of prochiral allylic alcohols. The asymmetric induction is achieved by adding an enantiomerically enriched tartrate derivative.

What is Cram’s rule?

Cram’s rule: As stated by Donald Cram of UCLA in 1952, “In certain non-catalytic reactions that diastereomer will predominate, which could be formed by the approach of the entering group from the least hindered side when the rotational conformation of the C-C bond is such that the double bond is flanked by the two …

What is epoxidation process?

Epoxidation is the chemical reaction which converts the carbon–carbon double bond into oxiranes (epoxides), using a variety of reagents including air oxidation, hypochlorous acid, hydrogen peroxide, and organic peracid (Fettes, 1964).

What is epoxidation give the suitable example?

If an atom is electrophilic, but also has a lone pair to donate, that cyclic transition state can lead to the product in one step. Alkene epoxidation is another example of this kind of reaction. An epoxidation is the transfer of an oxygen atom from a peroxy compound to an alkene.

Which reagent is used for Sharpless asymmetric Dihydroxylation?

These four reagents are commercially available premixed (“AD-mix”). The mixture containing (DHQ)2-PHAL is called AD-mix-α, and the mixture containing (DHQD)2-PHAL is called AD-mix-β….

Sharpless asymmetric dihydroxylation
Named after	Karl Barry Sharpless
Reaction type	Addition reaction
Reaction

What is Cram’s chelation model?

Chelation model According to Reetz, the Cram-chelate model for 1,2-inductions can be extended to predict the chelated complex of a β-alkoxy aldehyde and metal. The nucleophile is seen to attack from the less sterically hindered side and anti- to the substituent Rβ, leading to the anti-adduct as the major product.

What is felkin Ahn model?

In Felkin-Ahn model, a nucleophile comes from the least hindered side. The best way to do Felkin-Ahn model is to draw a newmen projection. Then have the nucleophile attack from the smallest group. Felkin-Ahn model example: Here, the model shows that the nucleophile prefers to attack from the least hindered side.

Why is epoxidation important?

Epoxides are an important class of compounds in organic synthesis, because nucleophilic ring opening takes place easily in an SN2 pathway with inversion of configuration at the reacting carbon center. The driving force of the high reactivity is the inherent strain of the three-membered heterocycle.

How do you prepare epoxides?

Epoxides (also known as oxiranes) are three-membered ring structures in which one of the vertices is an oxygen and the other two are carbons. The most important and simplest epoxide is ethylene oxide which is prepared on an industrial scale by catalytic oxidation of ethylene by air.

Is epoxidation electrophilic?

If an atom is electrophilic, but also has a lone pair to donate, that cyclic transition state can lead to the product in one step. Alkene epoxidation is another example of this kind of reaction.

What is the henbest epoxidation?

2.1 Epoxidation. In 1959, Henbest and Wilson found that cyclic allylic alcohols of ring sizes 5–7 react with m-chloroperbenzoic acid (mCPBA) to give syn-epoxides exclusively (Henbest phenomenon).

What is Cram’s rule with example?

For example, in sodium borohydride the sodium ion cannot from a bivalent complex. On the other hand, zinc borohydride could form a divalent chelation complex between the carbonyl oxygen and the electronegative atom. This is called Cram-chelation complex, which leads to a Cram-chelate product.

What is Cram’s rule in chemistry?

What is Sharpless epoxidation?

The Sharpless Epoxidation allows the enantioselective epoxidation of prochiral allylic alcohols. The asymmetric induction is achieved by adding an enantiomerically enriched tartrate derivative.

What is the difference between the Sharpless and Jacobsen epoxidation methods?

The Sharpless epoxidation has been used for the total synthesis of various carbohydrates, terpenes, leukotrienes, pheromones, and antibiotics. The main drawback of this protocol is the necessity of the presence of an allylic alcohol. The Jacobsen epoxidation, an alternative method to enantioselectively oxidise alkenes,…

How do you predict the chirality of a Sharpless epoxidation?

The chirality of the product of a Sharpless epoxidation is sometimes predicted with the following mnemonic. A rectangle is drawn around the double bond in the same plane as the carbons of the double bond (the xy-plane ), with the allylic alcohol in the bottom right corner and the other substituents in their appropriate corners.

What is the structure of the catalyst in the epoxidation reaction?

The structure of the catalyst is uncertain although it is thought to be a dimer of [Ti (tartrate) (OR) 2 ]. The epoxidation of allylic alcohols is a well-utilized conversion in fine chemical synthesis.