Asymmetric nucleophilic epoxidation organic reactions wiki. General mechanism o n n o o r 3 r 3 r 2 r r 1 2 r 1 mn still contraversial 97ang2060 possibilities m o r r 1 m o m o r r 1 concerted stepwise radical or polar oxametallocycle oxidations proceed with a degree of scrambling of geometry tbu et ph co 2et tms 99. Jacobsen epoxidation of hydroxy sulfonyl diene 4a and cyclization with csa. They extensively studied different facets of this reaction to convert it into one of the most useful and widely applicable methods for the epoxidation of. Recent investigations have shown that the mechanism of the epoxidation is strongly dependent on the substitutents of the alkene and on the reaction conditions. Mechanism and stereochemistry prediction in jacobsen. Understanding the mechanism of the epoxidation and the origin of asymmetric induction can lead to the development of new efficient catalysts and therefore is actively pursued 519. The manganese atom transfers an oxygen atom from chlorine bleach or similar oxidant. Such symmetry is useful in ligand design, furnishing predictable and repetitive structural units which reduce the number of diastereomeric transition states ho oh o ro o or ti o o e ti o. The first report on the epoxidation of olefins with iodosylbenzene as terminal oxidant and mniiisalen complexes as catalyst was published by kochi et al. The jacobsen epoxidation allows the enantioselective formation of epoxides from various cissubstituted olefins by using a chiral. Pdf probing competitive enantioselective pathways operating.
The application of organocatalytic asymmetric epoxidation. Naocl mnsalen catalyst ch 2 cl 2 r 1 r 2 o h h r 1 r 2 r 3 r3co 3 h r 2 o h r 3 r 1 r 1 r 2 oxone h 2 o,ch 3 cn ph 10. The report by kochi and coworkers in 1986 that a salen manganeseiii complex mnsalen complex was an efficient epoxidation catalyst for simple olefins 66 quickly led to independent reports from the groups of jacobsen 67 and katsuki 68 that chiral mnsalen complexes could catalyze asymmetric epoxidation reactions. Mechanistic study of the jacobsen asymmetric epoxidation. It is complementary to the sharpless epoxidation used to form epoxides from the double bond in allylic alcohols. The axial ligand, 43phenylpropylpyridine noxide p3no, increases the rate of epoxidation without affecting enantioselectivity and also stabilizes the catalyst. The enantioselectivity is explained by either a topon approach jacobsen or by a sideon approach katsuki of the olefin. Article pdf available in helvetica chimica acta 924. The sharpless asymmetric epoxidation only works with allylic alcohols, as illustrated by the conversion of 156 to 157 or 158 to 159. Jacobsens method of epoxidation of an alkene essay sample. Understanding the mechanism of the epoxidation and the origin of asymmetric induction can lead to the development of new efficient.
This process is experimental and the keywords may be updated as the learning algorithm improves. Alahmdi in the field of research of target natural product synthesis, catalytic asymmetric synthesis has. Highly diastereoselective katsuki jacobsen oxidation epoxidation of. The jacobsen epoxidation, sometimes referred to as jacobsen katsuki epoxidation is a chemical reaction which allows enantioselective epoxidation of unfunctionalized alkyl and aryl substituted alkenes. The jacobsen epoxidation, sometimes also referred to as jacobsen katsuki epoxidation is a chemical reaction which allows enantioselective epoxidation of unfunctionalized alkyl and aryl substituted olefins. The jacobsen epoxidation gains its stereoselectivity from a c2 symmetric.
In independent work, katsuki and jacobsen showed that asymmetric epoxidation occurs using manganesesalen catalysts in the presence. The jacobsenkatsuki epoxidation and its controversial. These keywords were added by machine and not by the authors. Catalytic asymmetric epoxidation of alkenes has been the focus of many research efforts over the past two decades, the best known methods probably being those developed by sharpless 1 and jacobsen katsuki.
The jacobsen epoxidation, sometimes also referred to as jacobsen katsuki epoxidation is a chemical reaction which allows enantioselective epoxidation of unfunctionalized alkyl and aryl substituted alkenes. The enantioselectivity of the jacobsen epoxidation is generally highest with conjugated cyclic olefins as substrates. The mechanism of the jk epoxidation is not fully understood, but most likely a manganesev species is the reactive intermediate, which is formed upon the oxidation of the mniiisalen complex. Jacobsenkatsuki epoxidation request pdf researchgate. Jacobsens method of epoxidation of an alkene essay example. Epoxidation of unfunctionalized olefins by mnsalen. Enantioselective organocatalytic epoxidation using hypervalent iodine reagents sandra lee and david w.
Epoxidation of neralgeranial using a jacobsen katsuki mn catalyst by chemical and electrochemical methods 5 compound with significant potential in the pharmaceutical and chemical industries given its broad applications ranging from the generation of citric flavors and aromas to the synthesis of organic macromolecules 2831. In this video, i have discussed about the mechanism of jacobsen epoxidation. General mechanism o n n o o r 3 r 3 r 2 r r 1 2 r 1 mn still contraversial 97ang2060 possibilities m o r r 1 m o m o r r 1 concerted stepwise radical or polar oxametallocycle oxidations proceed with a degree of scrambling of geometry tbu et. Selectivity enhancement for the jacobsenkatsuki epoxidation in fluorinated solvents. The chiral epoxide synthesized was then characterized with gcms and nmr. Dec 22, 2003 radicals or manganaoxetaneswhat are the intermediates in the jacobsenkatsuki epoxidation see scheme on the right. Jacobsen katsuki epoxidation prilezhaev reaction shi expoxidation r 1 r 2 aq. Highly enantioselective kochijacobsenkatsuki epoxidation of unfunctionalized olefins with mniiisalenbased chiral catalyst provides an efficient route to optically active epoxides 14. Request pdf radical intermediates in the jacobsen katsuki epoxidation insight into the controversial mechanism of the mn salencatalyzed epoxidation of olefins is provided in a theoretical. Jacobsenkatsuki epoxidation in name reactions in heterocyclic chemistry, li. Simple alkenes are oxidized with highasymmetric induction the socalled jacobsenkatsuki reaction.
Highly diastereoselective katsuki jacobsen oxidation. Probing competitive enantioselective pathways operating in the jacobsen katsuki epoxidation. Rate enhancement and enantioselectivity of the jacobsen. Mechanism, references and reaction samples of the jacobsenkatsuki asymmetric epoxidation. The enantioselective epoxidation of unfuctionalized olefins by optically active mn iii salen complexes has become a very important and versatile tool for organic. Pitt chem 2320 jacobsen katsuki epoxidations gradebuddy. Pdf selectivity enhancement for the jacobsenkatsuki. Jacobsen hydrolytic kinetic reasolution jacobsen hkr. While the practical utility of this protocol is indisputable, the mechanistic underpinnings have been the matter of some debate. Only a few years after this key publication an asymmetric version of this epoxidation was reported by the groups of jacobsen 18 and katsuki 19 using chiral mniiisalen. Jacobsen s catalyst was used to catalyze the epoxidation of an unknown alkene with a bleach solution that was buffered in order to maintain a ph of 9. The protocol developed by jacobsen and katsuki for the salenmn catalyzed. Probing competitive enantioselective pathways operating in.
Application in process chemistry thl 1995, 36, 3993. Jacobsen epoxidation an overview sciencedirect topics. In comprehensive asymmetric catalysis, 1st ed jacobsen, e. The oxidant for the epoxidation is tert butyl hydroperoxide. Jan 01, 2001 a breakthrough was the introduction of chiral manganesesalen catalysts by jacobsen and co. Jacobsen epoxidation of hydroxy sulfonyl diene ent4a.
Katsuki jacobsen oxidation epoxidation of acyclic alphasilyloxy sulfinyl dienes, followed by acidpromoted cyclization, leads to 2,5transsulfonyl dihydrofurans with good selectivities. Selectivity enhancement for the jacobsenkatsuki epoxidation in. Macmillan division of chemistry and chemical engineering, california institute of technology, pasadena, ca 91125, usa received 29 june 2006. The asymmetric epoxidation of indene using aqueous naocl, catalyzed by jacobsens chiral manganese salen complex, provides indene oxide in 90% yield and 85. Epoxidation of neralgeranial using a jacobsenkatsuki mn. The asymmetric induction is achieved by adding an enantiomerically enriched tartrate derivative. By changing the catalyst it is now possible to convert simple alkenes to the corresponding epoxide with highasymmetric induction. In this example, a stoichiometric amount of titanium and dipt was necessary for high conversion. The jacobsen epoxidation, sometimes also referred to as jacobsenkatsuki epoxidation is a. Compared to the sharpless epoxidation, the jacobsen epoxidation allows a broader substrate scope for the transformation. Enantioselective organocatalytic epoxidation using. Mechanistic study of the jacobsen asymmetric epoxidation of. Jacobsenkatsuki epoxidation organic chemistry portal. Myers sharpless asymmetric epoxidation reaction chem 115.
This ph minimizes the amount of side reactions that could occur such as hydrolysis of the epoxide. The jacobsen epoxidation involves the enantioselective transformation of cissubstututed alkenes to epoxides using a manganesesalen complex as a catalysts. Examples of the sharpless asymmetric epoxidation reaction in industry. The jacobsen katsuki epoxidation and its controversial mechanism. Mniiisalencatalyzed asymmetric epoxidation of zolefins. The application of organocatalytic asymmetric epoxidation mohammed i. Jacobsen and coworkers now at harvard university published the first of several important papers on the enantioselective epoxidation of unfunctionalized olefins catalyzed by chiral manganese complexes. Various types of reactions were completed to first create and then use jacobsens catalyst in the asymmetric epoxidation of an unknown alkene with bleach in the laboratory. In this example, excess tbhp was quenched with triethylphosphite instead of feii sulfate.
The classic example, the weitzscheffer reaction employs hydrogen peroxide under basic conditions z. Radical intermediates in the jacobsen katsuki epoxidation. Epoxidation of unfunctionalized olefins by mnsalen catalyst. Jacobsen s catalyst o o r 4 r 2 r 3 r 1 r 1 r 2 r 3 r 4 o r 1 r 2 r 3 r 4 or. Epoxidation reactions have been established as an important method for. The jacobsenkatsuki epoxidation and its controversial mechanism.
Feb 04, 2000 radical intermediates in the jacobsen katsuki epoxidation radical intermediates in the jacobsen katsuki epoxidation cavallo, luigi. Apr 20, 2004 highly enantioselective kochijacobsenkatsuki epoxidation of unfunctionalized olefins with mn iii salenbased chiral catalyst provides an efficient route to optically active epoxides 14. The asymmetric epoxidation of indene using aqueous naocl, catalyzed by jacobsen s chiral manganese salen complex, provides indene oxide in 90% yield and 85. How to predict the stereochemistry in the product and assign the rs configurati. The sharpless epoxidation allows the enantioselective epoxidation of prochiral allylic alcohols. Katsuki epoxidation and its controversial mechanism.
Epoxidation definition of epoxidation by merriamwebster. Na me reactions a collection of detailed reaction mechanisms, jie jack li, jacobsen katsuki epoxidation. Epoxidation definition is a conversion of a usually unsaturated compound into an epoxide. Sharpless asymmetric epoxidation mcmaster university. Understanding the mechanism of the epoxidation and the origin of asymmetric induction can lead to the development of new efficient catalysts and. The use of the cocatalyst p 3no allowed for a decreased charge of the mn salen catalyst in the jacobsen epoxidation. P wipf chem 2320 1 2 15 2006 9 jacobsen katsuki epoxidations jacobsen jacs 1990 112 2801 jacs 1991 1 7063 katsuki thl 1990 31 7345 based on kochi s. Jacobsen epoxidation and cyclization with csa of hydroxy sulfinyl diene 3a. The reaction is named after its inventor, eric jacobsen, currently of harvard university.
Mn mediated epoxidation of alkenes the jacobsen katsuki epoxidation. The jacobsen epoxidation allows the enantioselective formation of epoxides from various cissubstituted olefins by using a chiral mnsalen catalyst and a stoichiometric oxidant such as bleach. The jacobsen and katsuki have reported the improvement of olefin epoxidation, using a sophisticated chiral salen ligand for manganese complexes, which resulted in high enantioselectivity. Mechanism in general, three different mechanisms possible for metal oxo epoxidation. Jacobsenkatsuki epoxidation prilezhaev reaction shi expoxidation r 1 r 2 aq. Jacobsen epoxidation and cyclization with csa of hydroxy sulfinyl diene 2a.
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