Epoxidations, asymmetric chiral ketone-catalyzed

Chiral ketone-catalyzed asymmetric epoxidation has received intensive interest since the first reported by Curci et al. in 1984. The reaction is performed with oxone (potassium peroxomonosulfate) as the primary oxidant which generates the chiral dioxirane catalytic species in situ, which in turn, transfers the oxygen... 

Frohn, M. Shi, Y. Chiral Ketone-Catalyzed Asymmetric Epoxidation of Olefins, Synthesis 2000, 1979-2000. 

Shi asymmetric epoxidation Chiral-ketone catalyzed epoxidation of unfunctionalized olefins. 410... 

Chiral ketone-catalyzed asymmetric epoxidation of olefins 00S1979. 

The asymmetric epoxidation of alkenes constitutes a powerful approach to enantiomerically enriched epoxides, a class of highly versatile intermediates in organic synthesis [1]. Various effective epoxidation systems have been developed, including epoxidation of allylic [2, 3] and homoallylic [4] alcohols, metalunfunctionalized alkenes [5-7], and the nucleophilic epoxidation of electron-deficient alkenes [8]. During the past 10-15 years, much effort has been devoted to chiral ketone-catalyzed asymmetric epoxidation (Scheme 3.1). The subject has been described in great detail in the first edition [9] and other reviews [10]. This chapter provides an update on progress in this area since the first edition [9]. 

Warren JD, Shi Y. Chiral ketone-catalyzed asymmetric epoxidation of 2, 2-disubstituted vinylsilanes. J. Org. Chem. 1999 64(20) 7675-7677. 

For recent reviews on chiral ketone catalyzed asymmetric epoxidation see ... 

Various catalytic or stoichiometric asymmetric syntheses and resolutions offer excellent approaches to the chiral co-side chain. Among these methods, kinetic resolution by Sharpless epoxidation,14 amino alcohol-catalyzed organozinc alkylation of a vinylic aldehyde,15 lithium acetylide addition to an alkanal,16 reduction of the corresponding prochiral ketones,17 and BINAL-H reduction18 are all worth mentioning. 

Abstract Organo-catalyzed asymmetric epoxidation has received much attention in the past 30 years and significant progress has been made for various types of olefins. This review will cover the advancement made in the field of chiral ketone and chiral iminium salt-catalyzed epoxidations. 

Sharpless asymmetric epoxidation of allylic alcohols, asymmetric epoxidation of conjugated ketones, asymmetric sulfoxidations catalyzed, or mediated, by chiral titanium complexes, and allylic oxidations are the main classes of oxidation where asymmetric amplification effects have been discovered. The various references are listed in Table 4 with the maximum amplification index observed. 

Scheme 12.2 Asymmetric epoxidation catalyzed by C2-symmetrical chiral ketones 4. (For experimental details see Chapter 14.13.4).

Chen, R., Qian, C. and de Vries, J. G. Asymmetric epoxidation of a,/ -unsaturated ketones catalyzed by chiral ytterbium complexes, Tetrahedron Lett., 2001, 42, 6919-6921. 

Since the pioneering report of Curci in 1984 that a chiral ketone can catalyze asymmetric epoxidation reactions (methylcyclohexene oxide produced with up to 12% ee using (- -)-isopinocamphone/KHSOs) <1984CC155>, this area has attracted considerable interest with particular advances being achieved in the past decade by numerous research groups. 

Ketone-catalyzed asymmetric and diastereoselective epoxidation of olefins by di-oxiranes generated in situ from chiral ketones and oxone (2KHS05 KH-S04 K2S04) 04ACR497. 

Organocatalytic Oxidation. Asymmetric Epoxidation of Olefins Catalyzed by Chiral Ketones and Iminium Salts Wong, O.A. Shi, Y. Chem. Rev. 2008,108,3958. 

Wong OA, Shi Y. Organocatalytic oxidation. Asymmetric epoxidation of olefins catalyzed by chiral ketones and imi-nium salts. Chem. Rev. 2008 108 3958-3987. 

Zhang Z, Tang J, Wang X, Shi H. Chiral ketone- or chiral amine-catalyzed asymmetric epoxidation of cis-l-propenyl-phosphonic acid using hydrogen peroxide as oxidant. J. Mol. Catal. A Chem. 2008 285 68-71. 

Epoxides are very versatile intermediates, and asymmetric epoxidation of olefins is an effective approach to the synthesis of enantiomericaUy enriched epoxides [1-3]. Great success has been achieved for the epoxidation of allyhc alcohols [1], the metal-catalyzed epoxidation of unfunctionalized olefins (particularly conjugated cis- and tri-substituted) [2], and the nucleophilic epoxidation of electron-deficient olefins [3]. In recent years, chiral dioxiranes have been shown to be powerful agents for asymmetric epoxidation of olefins. Dioxiranes can be isolated or generated in situ from Oxone (potassium peroxymonosulfate) and ketones (Scheme 3.1) [4,5]. When the di-oxirane is used in situ, the corresponding ketone is regenerated upon epoxidation. Therefore, in principle, a catalytic amount of ketone can be used. When a chiral ketone is used, asymmetric epoxidation should also be possible [6]. Extensive studies have been carried out in this area since the first chiral ketone was reported by Curd in 1984 [7]. This chapter describes some of the recent progress in this area. 

A more versatile method to use organic polymers in enantioselective catalysis is to employ these as catalytic supports for chiral ligands. This approach has been primarily applied in reactions as asymmetric hydrogenation of prochiral alkenes, asymmetric reduction of ketone and 1,2-additions to carbonyl groups. Later work has included additional studies dealing with Lewis acid-catalyzed Diels-Alder reactions, asymmetric epoxidation, and asymmetric dihydroxylation reactions. Enantioselective catalysis using polymer-supported catalysts is covered rather recently in a review by Bergbreiter [257],... 

Asymmetric epoxidation of olefins is an effective approach for the synthesis of enan-tiomerically enriched epoxides. A variety of efficient methods have been developed [1, 2], including Sharpless epoxidation of allylic alcohols [3, 4], metal-catalyzed epoxidation of unfunctionalized olefins [5-10], and nucleophilic epoxidation of electron-deficient olefins [11-14], Dioxiranes and oxazirdinium salts have been proven to be effective oxidation reagents [15-21], Chiral dioxiranes [22-28] and oxaziridinium salts [19] generated in situ with Oxone from ketones and iminium salts, respectively, have been extensively investigated in numerous laboratories and have been shown to be useful toward the asymmetric epoxidation of alkenes. In these epoxidation reactions, only a catalytic amount of ketone or iminium salt is required since they are regenerated upon epoxidation of alkenes (Scheme 1). 

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