Jacobsen-Katsuki reaction

Equation 12.16 is an example of the Sharpless-Katsuki asymmetric epoxi-dation of allylic alcohols, which is catalyzed by a Ti complex bound to a chiral tartrate ligand.38 A Mn-salen39 complex serves as catalyst for asymmetric epoxi-dation (Jacobsen-Katsuki reaction) of a wide variety of unfunctionalized alkenes, shown in equation 12.17.40 0s04 complexed with chiral alkaloids, such as quinine derivatives (equation 12.18), catalyzes asymmetric 1,2-dihydroxylation of alkenes (known as the Sharpless asymmetric dihydroxylation).41 The key step of all these transformations is the transfer of metal-bound oxygen, either as a single atom or as a pair, to one face of the alkene. 

Many attempts were undertaken to produce chiral epoxides for chemical syntheses. This can be achieved by the use of chiral catalysts. The first applicable and relatively simple procedure of chemical chiral epoxidations was described by Katsuki and Sharpless [2], later called the Katsuki-Sharpless epoxidation. In this reaction, allyl alcohols are epoxi-dized in the presence of tartrate esters, e.g., (—)-diethyl tartrate. This allows the production of either (/ )- or (S)-epoxides depending on the selection of (R)- or (5)-tartrate ester as chir additive. However, the reaction is limited to ally lie alcohols and is somewhat sensitive to steric hindrances. In the meantime, a number of different catalysts have been developed for the epoxidation of cw-alkenes. The Jacobsen-Katsuki reaction allows the epoxidation of fran5-alkenes and terminal olefins [3]. All of these approaches, however, are limited to the epoxidation of activated double bonds like allylic alcohols or require expensive catalysts, and usually the regiospecificity of these reactions is not sufficient for practical applications. Furthermore, the chiral catalysts, although usually they can be recycled, are often very exj nsive. 

The Jacobsen-Katsuki epoxidation reaction is an efficient and highly selective method for the preparation of a wide variety of structurally and electronically diverse chiral epoxides from olefins. The reaction involves the use of a catalytic amount of a chiral Mn(III)salen complex 1 (salen refers to ligands composed of the N,N -ethylenebis(salicylideneaminato) core), a stoichiometric amount of a terminal oxidant, and the substrate olefin 2 in the appropriate solvent (Scheme 1.4.1). The reaction protocol is straightforward and does not require any special handling techniques. 

One of the most significant developmental advances in the Jacobsen-Katsuki epoxidation reaction was the discovery that certain additives can have a profound and often beneficial effect on the reaction. Katsuki first discovered that iV-oxides were particularly beneficial additives. Since then it has become clear that the addition of iV-oxides such as 4-phenylpyridine-iV-oxide (4-PPNO) often increases catalyst turnovers, improves enantioselectivity, diastereoselectivity, and epoxides yields. Other additives that have been found to be especially beneficial under certain conditions are imidazole and cinchona alkaloid derived salts vide infra). 

Initial studies on the Jacobsen-Katsuki epoxidation reaction identified conjugated eyelie and acyelic cw-disubstituted olefins as the class of olefins best suited for the epoxidation reaetion. " Indeed a large variety of c/s-disubstituted olefins have been found to undergo epoxidation with a high degree of enantioselectivity. 2,2"-Dimethylehromene derivatives are especially good substrates for the epoxidation reaetion. Table 1.4.1 lists a variety of examples with their corresponding reference. 

The Jacobsen-Katsuki epoxidation reaction has found wide synthetic utility in both academia and industrial settings. As described previously, the majority of olefin classes, when conjugated, undergo Mn(salen)-catalyzed epoxidation in good enantioselectivity. In this section, more specific synthetic utilities are presented. 

The first application of the Jacobsen-Katsuki epoxidation reaction to kinetic resolution of prochiral olefins was nicely displayed in the total synthesis of (+)-teretifolione B by Jacobsen in 1995. 

Jacobsen-Katsuki epoxidation reaction in total synthesis Scheme 1.4.11... 

The Jacobsen-Katsuki epoxidation reaction has been widely used for the preparation of a variety of structurally diverse complex molecules by both academia and the pharmaceutical industry. Summarized below are a few examples. 

Palucki, M. Jacobsen-Katsuki epoxidation In Name Reactions in Heterocyclic Chemistry, Li, J. J. Corey, E. J., Eds. Wiley Sons Hoboken, NJ, 2005, 29—43. (Review). 

Oxone. DMD. Sharpless Evoxidation. Jacobsen-Katsuki EnoxUlation. Corev-Chavkovskv reagent and Reaction. Shi (Asymmetric) Evoxidation. 

There are several remarkable features of these immobilized salens, notably the fact that the dendritic branches do not appear to decrease the catalytic activity with respect to the complexes in solution. Moreover, the reactions with dendritic catalysts incorporated in polystyrene gave products of essentially the same enantiopurity as those observed in homogeneous solution, with the dendritically substituted or with the original Jacobsen-Katsuki complexes. Some of the Mn-loaded beads were stored for a year without loss of activity. Especially, the biphenyl- and acetylene-linked salen polymers gave Mn complexes of excellent performance, which after ten catalytic rims showed no loss of enantioselectivity or degree of conversion. 

High-valent oxo-complexes, isolated or in situ-generated, interact most often with electron-rich n -systems 1 or suitable C-H bonds with low bond dissociation energy (BDE) in substrates 3 (Fig. 2). These reactions may occur concerted via transition states 1A or 3A leading to epoxides 2 or alcohols 4. On the other hand, a number of epoxidation reactions, such as the Jacobsen-Katsuki epoxidation, is known to proceed by a stepwise pathway via transition state IB to radical intermediate 1C [39]. Similarly, hydrocarbon oxidation to 4 can proceed by a hydrogen abstraction/S ... 

Epoxides are a very versatile class of compounds and the interest in catalytic epoxidation reactions is very high.70,71 They are the key raw materials in the syntheses of a wide variety of chemicals. A number of compounds have been shown to be catalytically active, but the regular laboratory reagents for epoxidations are generally methyl trioxorhenium(VII)72-81 and the Jacobsen-Katsuki-catalysts82-94 which can even introduce chirality. They are also theoretically well investigated95-106 and are described below. 

This past year s literature has shown extraordinary activity in this realm. Perhaps the most firmly entrenched methodology for the preparation of chiral epoxides is the metallosalen mediated epoxidation of unfunctionalized alkenes (the Jacobsen-Katsuki epoxidation), which has been recently reviewed <03SL281 >. It is widely accepted that this reaction proceeds through an 0X0 intermediate, and that the observed enantioselectivities depend upon the electronic stability of this species. For example, Jacobsen found empirically that electron-donating substituents in the 5 and 5 positions of catalyst 1 gave better enantioselectivities <91JA6703>. More recent... 

The body of work that constitutes the metallosalen-catalyzed (Jacobsen-Katsuki) asymmetric epoxidation reaction is far too extensive to be detailed here however, it has been comprehensively reviewed <1996JM087, B-1999M1(11)649, B-2000MI287, 2001COR663, 2005CRV1563>. Rather, after some introductory remarks, we will highlight examples in which ring-fused oxiranes are produced. 

Related reactions Jacobsen-Katsuki epoxidation, Prilezhaev oxidation, Rubottom oxidation, Sharpless asymmetric epoxidation, Shi... 

Adam, W., Mock-Knobiauch, C., Saha-Moeiier, C. R., Herderich, M. Are Mn " Species Involved in Mn(Salen)-Catalyzed Jacobsen-Katsuki Epoxidations A Mechanistic Eiucidation of Their Formation and Reaction Modes by EPR Spectroscopy, Mass-Spectral Analysis, and Product Studies Chiorination versus Oxygen Transfer. J. Am. Chem. Soc. 2000, 122, 9685-9691. 

Related reactions Davis oxaziridine oxidation, Jacobsen-Katsuki epoxidation, Priiezhaev reaction, Shi asymmetric epoxidation ... 

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