Jacobsen-Katsuki asymmetric

Fig. 4.99 The Jacobsen-Katsuki asymmetric epoxidation of unfunctionalized olefins.

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. 

Kinetic resolution in the catalytic conversion of racemic chloro propanols to optically active epoxides has been achieved by use of a chiral Co(salen) type complex in combination with K2CO3. Although enantioselectivity was modest (< 35 % ee), this first use in asymmetric epoxide formation of the chiral ligand system that was later brought to fame through the Jacobsen-Katsuki asymmetric epoxidation is noteworthy [56,57]. When applied to the prochiral l,3-dichloro-2-propanol, asymmetric induction of up to ca. 60 % ee was achieved (Sch. 8) [58]. 

Figure 17.32 Use of the Jacobsen-Katsuki asymmetric epoxidation for the preparation of an e.p. intermediate for preparation of structure 92...

The Best results are obtained with cA-alkenes however, the epoxidation of tri-and tetra-substituted double bonds is also possible. Because of its versatility, the Jacobsen-Katsuki epoxidation is an important method in asymmetric synthesis. 

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

The potential of a catalytic process for use on a large scale can be a good indication of its efficiency. During recent decades there has been an increasing tendency to apply asymmetric catalytic processes in industry [1], The asymmetric Noyori hydrogenation [2] and the Sharpless and Jacobsen-Katsuki epoxidation [3] are representative examples of impressive developments in this field [1]. 

In practice in the literature of the past 20 years the important results with ruthenium in epoxidation are those where ruthenium was demonstrated to afford epoxides with molecular oxygen as the terminal oxidant. Some examples are presented (see later). Also ruthenium complexes, because of their rich chemistry, are promising candidates for the asymmetric epoxidation of alkenes. The state of the art in the epoxidation of nonfunctionalized alkenes is namely still governed by the Jacobsen-Katsuki Mn-based system, which requires oxidants such as NaOCl and PhIO [43,44]. Most examples in ruthenium-catalysed asymmetric epoxidation known until now still require the use of expensive oxidants, such as bulky amine oxides (see later). 

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

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

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. 

Chiral Mn salen complexes have been prepared by replacing ethylenediatnine with a chiral diamine such as 1,2-cyclohexanediamine, and these complexes show very high enantioselectivity in the epoxidation of alkenes, especially cyclic ones. The Mn-catalyzed asymmetric epoxidation of alkenes is known as the Jacobsen or Jacobsen-Katsuki epoxidation. 

Asymmetric epoxidation of ds-substituted conjugated alkenes can be achieved efficiently using the Jacobsen-Katsuki conditions (see Section 5.2, Scheme 5.66). For the enantiomer 9, use the (5,5)-(salen)Mn(III)Cl catalyst and NaOCl in CH2CI2 at 4 °C in the presence of an additive such as pyridine A-oxide. 

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