Epoxidation catalyst for

It seems that silver is a unique epoxidation catalyst for ethylene. All other catalysts are relatively ineffective, and the reaction to ethylene is limited among lower olefins. Propylene and butylenes do not form epoxides through this route. ... 

Binaphthol- and biphenyl-derived ketones (9 and 10) were reported by Song and coworkers in 1997 to epoxidize unfunctionalized alkenes in up to 59% ee (Fig. 3, Table 1, entries 9, 10) [37, 38]. Ketones 9 and 10 were intended to have a rigid conformation and a stereogenic center close to the reacting carbonyl group. The reactivity of ketones 9 and 10 is lower than that of 8, presumably due to the weaker electron-withdrawing ability of the ether compared to the ester. In the same year, Adam and coworkers reported ketones 11 and 12 to be epoxidation catalysts for several trans- and trisubstituted alkenes (Table 1, entries 11,12). Up to 81% ee was obtained for phenylstilbene oxide (Table 1, entry 25) [39]. 

In 1996, ketone 26 was reported to be a highly effective epoxidation catalyst for a variety of trans- and trisubstituted olefins [53]. Ketone 26 can be readily synthesized from D-fructose by ketalization and oxidation (Scheme 2) [54-56]. The enantiomer of ketone 26 (ent-26) can be obtained by the same methods from L-fructose, which can be obtained from L-sorbose [57, 58]. 

The report by Kochi and co-workers in 1986 that a (salen)manganese(lll) complex (Mn(salen) complex) was an efficient epoxidation catalyst for simple olefins <1986JA2309> quickly led to independent reports from the groups of Jacobsen <1990JA2801> and Katsuki <1990TL7345> that chiral Mn(salen) complexes could catalyze asymmetric epoxidation reactions. The reaction requires the use of a stoichiometric oxidant initially iodosylarenes were utilized, but it was quickly found that NaOCl was also successful. 

E. Pizzo, P. Sgarbossa, A. Scarso, R. A. Michelin, G. Strukul, Second-generation electron-poor platinum(II) complexes as efficient epoxidation catalysts for terminal alkenes with hydrogen peroxide, Organometallics 25 (2006) 3056. 

The grafting of a titanocene on to a MCM-41 support has been used to prepare a powerful epoxidation catalyst for substrates including pinene and smaller unsaturated molecules (Figure 4.4).70... 

More recently, Beller and coworkers have shown that the ruthenium complex 6 (Fig. 7.9) is an effective epoxidation catalyst, for a variety of olefins, with 3 equiv. of 30% H2O2 at very low catalyst loadings (0.005 mol%). A tertiary alcohol such as fert-amyl alcohol was used as a cosolvent. Based on its high activity and broad scope this system appears to have considerable synthetic potential, which may be adapted to afford effective asymmetric variants in the future. Indeed, a truly effective catalyst, with broad scope, for asymmetric epoxidation with aqueous hydrogen peroxide, preferably in the absence of organic solvents, is still an important and elusive goal in oxidation chemistry. 

In 1996, a fructose-derived ketone was identified by Shi and co-workers to be a highly reactive and enantioselective epoxidation catalyst for frtz 5-disubstituted and trisubstituted olefins." Good yields and high enantioselec-tivities can be obtained with 30 mol% of ketone 62 for a wide range of unfunctionalized ira 5-disubstituted and trisubstituted olefins (Scheme 35.16). The epoxidation is typically performed at pH around 10.5 by adding either potassium carbonate or potassium hydroxide into the... 

Although ketone 62 is an effective epoxidation catalyst for a variety of trans- and trisubstituted olefins, epoxidation of cis- and terminal olefins using this ketone led to rather poor enantioselectivity." " To improve the performance of asymmetric epoxidation of other types of olefins, a new class of chiral oxazolidinone ketone catalysts was explored (Scheme 35.17)." ° High enantioselectivity was obtained for asymmetric epoxidation of cis- and terminal olefins with ketones 65" and 66, respectively. 

In 1996, a fructose-derived ketone (39) was reported to be a highly effective epoxidation catalyst for a wide range of olefins (Scheme 3.25) [34]. The synthesis of ketone 39 can be readily achieved in two steps from D-fructose by ketahzation and oxidation [34-37]. The synthesis of the enantiomer of ketone 39 can be performed similarly from L-fructose, which can be prepared from readily available L-sorbose based on a literature procedure [35, 38]. Similar enantioselectivities were observed for the epoxidation with ketone ent-39 prepared in this way. 

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