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Asymmetric epoxidation catalytic reaction

The catalytic asymmetric epoxidation of a,p-unsaturated aldehydes has also been an important challenge in iminium catalysis and for chemical synthesis in general. More recently, Jprgensen and coworkers have developed an asymmetric organocatalytic approach to ot, (3-epoxy aldehydes using pyrrolidine catalyst 20 and H2O2 as the stoichiometric oxidant. The reaction appears to be extremely general and will likely receive wide attention from the chemical synthesis community (Scheme 11.6b). [Pg.325]

In conjunction with the chiral anion TRIP (156) (10 mol%), diamine 157 (10 mol%) can be used in the catalytic asymmetric epoxidation of a,p-unsaturated ketones (>90% ee) [196], while the secondary amine 158 (10 mol%) can be used for the epoxidation of both di- and trisubstituted a,P-unsaturated aldehydes (92-98% ee) (Fig. 15) [211], The facile nature of these reactions, using commercially available peroxides as the stoichiometric oxidant, together with the synthetic utility of the epoxide products suggests application in target oriented synthesis. [Pg.331]

The catalytic asymmetric epoxidation of a,/i-unsaturated carbonyl compounds is one of the synthetically useful reactions in organic synthesis.The resulting chiral epoxides are easily converted to various useful chiral compounds. We developed a new yttrium-(5)-6,6 -[oxybis(ethylene)dioxy]biphenyl-2,2 -diol (1) (Figure 6.10)... [Pg.239]

Success in the use of Ti tartrate catalyzed asymmetric epoxidation depends on the presence of the hydroxyl group of the allylic alcohol. The hydroxyl group enhances the rate of the reaction, thereby providing selective epoxidation of the allylic olefin in the presence of other olefins it also is essential for the achievement of asymmetric induction. The role played by the hydroxyl group in this reaction is described in a later section of this chapter. The need for a hydroxyl group necessarily limits the scope of this asymmetric epoxidation to a fraction of all olefins. Fortunately, allylic alcohols are easily introduced into synthetic intermediates and are very versatile in organic synthesis. The Ti tartrate catalyzed asymmetric epoxidation of allylic alcohols has been applied extensively as documented in the literature and in this review. The development of methods aimed at catalytic asymmetric epoxidation of unfunctionalized olefins is described in Chapter 6B, whereas the catalytic asymmetric dihydroxylation of olefins, which provides an alternate method for olefin functionalization, is described in Chapter 6D. [Pg.232]

The catalytic asymmetric epoxidation of electron-deficient olefins has been regarded as one of the most representative asymmetric PTC reactions, and various such systems have been reported (Scheme 3.12). Lygo reported the asymmetric epoxidation of chalcone derivatives through the use of NaOCl [30,31], while Shioiri and Arai used aqueous H202 as an oxidant, their results indicating hydrogen bonding between the catalyst and substrates because an OH functionality in the catalyst was essential... [Pg.40]

A catalytic asymmetric epoxidation reaction of a,/l-unsaturated esters via conjugate addition of an oxidant using chiral yttrium-biphenyldiol-Ph3As=0 complexes has been developed. Yields up to 90% and ees up to 99% have been achieved.43... [Pg.89]

Katsuki, T. Asymmetric Epoxidation of Unfunctionalized Olefins and Related Reactions, Catalytic Asymmetric Synthesis, Ojima, I. VCH New York, 2000, Chapter 6B, 287 and references therein. [Pg.485]

The first part of this chapter describes recent advances in the use of novel, chiral, alkali metal free-lanthanoid-BINOL derivative complexes for a variety of efficient, catalytic, asymmetric reactions. For example, using a catalytic amount of chiral Ln-BINOL derivative complexes, asymmetric Michael reactions and asymmetric epoxidations of enones proceed in a highly enantioselective manner. [Pg.202]

The catalytic asymmetric epoxidation of alkenes offers a powerful strategy for the synthesis of enantiomerically enriched epoxides and enantioselective oxidation reactions in ionic liquids have been summarised previously.[39] Complexes based on chiral salen ligands - usually with manganese(III) as the coordinated metal - often afford excellent yields and enantioselectivities and the catalytic cycle for the reaction is depicted in Scheme 5.5 J40 ... [Pg.96]

Asymmetric epoxidation The catalytic asymmetric epoxidation of alkenes has been the focus of many research efforts over the past two decades. The non-racemic epoxides are prepared either by enantioselective oxidation of a prochiral carbon-carbon double bond or by enantioselective alkylidenation of a prochiral C=0 bond (e.g. via a ylide, carbene or the Darzen reaction). The Sharpless asymmetric epoxidation (SAE) requires allylic alcohols. The Jacobsen epoxidation (using manganese-salen complex and NaOCl) works well with ds-alkenes and dioxirane method is good for some trans-alkenes (see Chapter 1, section 1.5.3). [Pg.292]

The procedure for catalytic asymmetric epoxidation of allyl alcohol coupled with in situ derivatization involves the same methodology detailed above for ( )-2-octenol. On a 1.0 mol scale using ( + )-diisopropyl L-tartrate the reaction was complete in 6 hours at — 5°C. [Pg.196]

The construction of strained three-membered ring systems remains a mainstay in organic synthesis. Catalytic asymmetric epoxidation and cyclo-propanation reactions continue to attract attention due to the inherent value of epoxides and cyclopropanes in pharmaceuticals and as synthons towards... [Pg.110]

The temperature required for the formation of diazoalkanes can be significantly decreased by using phase-transfer catalysis. This method has allowed the use of transition metals in the catalytic asymmetric epoxidation of carbonyl compounds (eq 19). The use of phase-transfer catalysis and moderate temperatures promotes the formation of diazoalkanes at a very low rate, achieving low concentrations of diazoalkane during the reaction, which is critical for the outcome of the process. The use of trisylhydrazone has shown better results in some cases compared to its tosyl analog. Presumably, the bulkier sulfonyl group may facilitate the... [Pg.626]

Based on these assumptions, the epoxidation of trans-P-methylstyrene was then performed under a different reaction pH [35, 41]. As shown in Figure 3.1, the reaction pH displayed a profound impact on the substrate conversion, and a higher pH was indeed beneficial to the catalyst efficiency, with more than a 10-fold increase in conversion from a lower pH (7-8) to a higher pH (>10). This dramatic pH effect led to a catalytic asymmetric epoxidation process, consequently enhancing the potential of ketone 39 for practical use. Typically, the epoxidation is performed at a pH of... [Pg.60]

Olefins are abundant and chemically stable points of departure for the generation of a wide variety of functionalities. Consequently, their chemo- and stereoselective elaboration continues to be of immense importance in the field of organic synthesis. Oxidative transformations of olefins include a wide variety of efficient and stereoselective synthetic reactions to access highly functionalized, chiral building blocks. In particular, the catalytic asymmetric epoxidation and dihydroxylation reactions constitute two of the most reliable and general enantioselective processes developed to date. [Pg.302]

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... [Pg.124]


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See also in sourсe #XX -- [ Pg.108 , Pg.109 ]




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