Olefins ketone-catalyzed epoxidation

Fig. 16. Proposed reaction mechanism for the olefin ketonation and epoxidation catalyzed by platinum-blues.

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

In efforts to expand the scope of the ketone catalyzed epoxidation, glucose-derived ketone 57 was reported to be an effective catalyst for the epoxidation of ds-olefms in 2000 (Scheme 3.44). High ee can be obtained for a number of both acychc and cyclic olefins (Scheme 3.44) [76-79]. The epoxidation is stereospecific and no isomeriza-... 

In this multi-authored book selected authors in the field of oxidation provide the reader with an up to date of a number of important fields of modern oxidation methodology. Chapter 1 summarizes recent advances on the use of green oxidants such as H2O2 and O2 in the osmium-catalyzed dihydroxylation of olefins. Immobilization of osmium is also discussed and with these recent achievements industrial applications seem to be near. Another important transformation of olefins is epoxidation. In Chapter 2 transition metal-catalyzed epoxidations are reviewed and in Chapter 3 recent advances in organocatalytic ketone-catalyzed epoxidations are covered. Catalytic oxidations of alcohols with the use of environmentally benign oxidants have developed tremendously during the last decade and in Chapter 4 this area is reviewed. Aerobic oxidations catalyzed by N-hydroxyphtahmides (NHPI) are reviewed in Chapter 5. In particular oxidation of hydrocarbons via C-H activation are treated but also oxidations of aUcenes and alcohols are covered. 

The epoxidation of electon-defident olefins using a nucleophilic oxidant such as an alkyl hydroperoxide is generally nonstereospecific epoxidation of both cis- and /nmv- ,/3-unsatii rated ketones gives the trans-epoxide preferentially. However, the epoxidation of cis-ofi-unsaturated ketones catalyzed by Yb-(40) gives civ-epoxides preferentially, with high enantioselectivity, because the oxidation occurs in the coordination sphere of the ytterbium ion (Scheme 26).132... 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

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. 

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). 

The results of the olefin oxidation catalyzed by 1 to 6 are summarized in Tables 1-3. Table 1 shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbornene) are selectively oxidized to epoxides. Cyclopentene shows an exceptional behavior it is oxidized exclusively to cyclopentanone without any produc-... 

Figure 8 Examples of oxygen transfer to different substrates using hydroperoxo or alkylperoxo species A, the epoxidation of olefins catalyzed by Mo (VI) complexes as in the Oxirane process B, the Baeyer-Villiger oxidation of ketones catalyzed by Pt(II) complexes C, the epoxidation of olefins catalyzed by Ti(IV) silicates D, the oxidation of organic sulfides catalyzed by V(V) complexes.

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

Asymmetric Epoxidation of Electron-deficient trans-Olefins. (f )-l can also catalyze epoxidation of electron-deficient trans -olefins, especially ( )-cinnamate derivatives (eq 4). With 5 mol % of (f )-l, epoxidation of acrylate (5) is completed in 27 h with 74% yield and 85% ee. The crude product can be purified using a continuous dissolution and crystallization process to afford enantiomerically pure product and recover the ketone catalyst simultaneously. A similar practical method has been employed for large-scale synthesis of a key intermediate for diltiazem hydrochloride (a potent calcium antagonist for treatment of cardiovascular disease). 

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

Chiral ketone-catalyzed asymmetric epoxidation of olefins 00S1979. 

Olefins can be epoxidized by dioxygen in the presence of an aldehyde and various metal complexes [54]. An analogous oxidation of alkanes gives alcohols, ketones and alkyl hydroperoxides. Examples of oxidations by dioxygen in the presence of various reducing agents catalyzed by transition metal complexes are given in Table IX.6. 

Selective epoxidation of polyene compound has also achieved with ent 2, the enantiomer of ketone 2. In Morimoto s total synthesis of polyether (+)-aurilol, Shi epoxidation was utilized twice, with ketone 2 and ent-2, respectively." Epoxidation of 79 with ketone 2 gave epoxide 80 with high diastereoselectivity. Epoxide 80 underwent acid catalyzed 5-exo-tet cyclization to produce tetrahydrofuran 81 with the desired stereochemistry. Subsequently, diene 82 was selectively epoxidized with ent-2 only at the trisubstituted olefin to give epoxide 83. Epoxides 80 and 83 played important roles in setting stereocenters in the final product. 

Epoxidation of olefins was catalyzed by the ruthenium(II) complex of the above perfluorinated y3-diketone in the presence of 2-methylpropanal (Scheme 50). Unfunctionalized olefins were epoxidized with a cobalt-containing porphyrin complex, and epoxidation of styrene derivatives was catalyzed by chiral salen manganese complexes (248) (Scheme 50). In the latter case, chemical yields were generally high, however, the products showed low enantiomeric excess with the exception of indene (92% ee). [Pd(C7Fi5COCHCOC7Fi5)2] efficiently catalyzed the oxidation of terminal olefins to methyl ketones with f-butylhydroperoxide as oxidant in a benzene-bromoperfluoro-octane solvent system (Scheme 50). In all these reactions, the product isolation and efficient catalyst recycle was achieved by a simple phase separation. 

Organocatalytic Oxidation. Ketone-catalyzed Asymmetric Epoxidation of Olefins... 

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. 

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