Designing New Chiral Ketone Catalysts. Asymmetric Epoxidation of <i>cis</i>-Olefins and Terminal Olefins

Tian, Hongqi; She, Xuegong; Yu, Hongwu; Shu, Lianhe; Shi, Yian

doi:10.1021/jo010838k

Cited by 123 publications

(65 citation statements)

References 29 publications

(20 reference statements)

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“…As shown in our earlier studies (94,95), planar M is favored over spiro L for ketone 2 because of the attractive interaction between the phenyl group of the olefin and the oxazolidinone moiety of the ketone catalyst, and 39% ee of the (S,S) isomer was obtained (Table 2 and Scheme 7). In stark contrast, when ketone 3 was used, 40% ee of the (R,R) isomer of the epoxide was obtained ( Table 2 and Scheme 7), indicating spiro N being favored over planar O.…”

Section: Methodssupporting

confidence: 55%

“…[93][94][95]. The higher ees obtained for styrenes with ketone 3 compared with 2 suggest that the replacement of the pyranose oxygen with a carbon has a noticeable impact on the competition between these transition states.…”

Section: Resultsmentioning

confidence: 99%

“…[52][53][54]. Chiral dioxiranes were shown recently to be effective for asymmetric epoxidation of trans-, trisubstituted , and certain cis-alkenes (92)(93)(94)(95). Asymmetric epoxidation of styrenes with chiral dioxiranes has been studied also (61,66,68,81,88,90,(93)(94)(95); however, the enantioselectivity has not exceeded 85% (93)(94)(95).…”

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confidence: 99%

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Highly enantioselective epoxidation of styrenes: Implication of an electronic effect on the competition between spiro and planar transition states

Hickey

Goeddel

Crane

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Asymmetric epoxidation of various styrenes using carbocyclic oxazolidinone-containing ketone 3 has been investigated. High enantioselectivity (89 -93% enantiomeric excess) has been attained for this challenging class of alkenes. Mechanistic studies show that substituents on the ketone catalyst can have electronic influences on secondary orbital interactions, which affects the competition between spiro and planar transition states and, ultimately, enantioselectivity. The results described herein not only reveal the potential of chiral dioxirane catalyzed asymmetric epoxidation as a viable entry into this important class of olefins but also further enhance the understanding of the mechanistic aspects of chiral ketone-catalyzed asymmetric epoxidation. Epoxides are important intermediates for the synthesis of complex molecules. Asymmetric epoxidation of prochiral alkenes presents a powerful strategy for the synthesis of enantiomerically enriched epoxides. Great progress has been made in the areas of asymmetric epoxidation of allylic alcohols (1-3), chiral metal complex-catalyzed epoxidation of unfunctionalized alkenes (particularly with conjugated cis-and trisubstituted alkenes) (4 -7), and asymmetric epoxidation of electron-deficient alkenes under nucleophilic conditions (8 -10). Styrene oxides are extremely useful and can be prepared by a number of methods such as asymmetric reduction of ␣-halo acetophenones (refs. 11 and 12 and references therein), asymmetric dihydroxylation of styrenes (13,14), and kinetic resolution of racemic epoxides (15). The asymmetric epoxidation of styrenes also has received a considerable amount of interest. Various chiral catalysts and reagents have been investigated for the epoxidation of styrenes, including chiral porphyrin complexes (16 -34), chiral salen complexes (35-42), chiral oxaziridines and oxaziridinium salts (43-46), and enzymes (47-51). Metal catalysts such as chiral porphyrin and salen complexes have been studied extensively for the epoxidation of these alkenes, and the enantioselectivities have reached the 80% range in a number of cases (21,23,29,31,37,38,40,41), with 96% enantiomeric excess (ee) being obtained in one case (3,5-dinitrostyrene) (23).Among other oxidants, dioxiranes either isolated or generated in situ are powerful epoxidation agents (Scheme 1; refs. 52-54). Chiral dioxiranes were shown recently to be effective for asymmetric epoxidation of trans-, trisubstituted (55-91), and certain cis-alkenes (92-95). Asymmetric epoxidation of styrenes with chiral dioxiranes has been studied also (61,66,68,81,88,90,(93)(94)(95); however, the enantioselectivity has not exceeded 85% (93-95). Generally speaking, the highly enantioselective epoxidation of styrenes still remains a formidable challenge.During our studies, we found that varying the catalyst structure could have a dramatic effect on enantioselectivity for the dioxirane-mediated epoxidation of styrene. Fructosederived ketone 1 (Scheme 2), a very effective catalyst for transand trisubstituted alkenes, gave only 24...

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Section: Methodssupporting

confidence: 55%

Section: Resultsmentioning

confidence: 99%

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Highly enantioselective epoxidation of styrenes: Implication of an electronic effect on the competition between spiro and planar transition states

Hickey

Goeddel

Crane

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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“…The related oxazolidinone ketone catalyst 304, prepared in six steps from D-glucose [362], has the advantage of exhibiting high ees for both cis-and terminal olefins [363]. Interestingly, for olefins with aromatic substituents, it appears that the transition state shows a preference for positioning the p-system proximal to the oxazolidinone moiety (as in 319), so that aromatic groups can be efficiently differentiated during the epoxidation.…”

Section: Using Dioxiranesmentioning

confidence: 99%

Three‐Membered Heterocycles. Structure and Reactivity

Murphree

2011

Modern Heterocyclic Chemistry

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“…To this was added the iminium salt as a solution in the solvent (0.5 ml per 0.1 g oxidant). This iminium salt solution was cooled to the same temperature as the solution containing the oxidant and added to it dropwise over [15][16][17][18][19][20] min; the temperature of the reaction vessel was monitored to minimize increase in temperature during the addition. A solution of the alkene in the reaction solvent (0.5 ml per 0.1 g oxidant) was added dropwise.…”

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confidence: 99%

Non-aqueous iminium salt mediated catalytic asymmetric epoxidation

et al. 2006

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Citation: PAGE et al, 2006. Non-aqueous iminium salt mediated catalytic asymmetric epoxidation. Tetrahedron 62 (28), pp. [6607][6608][6609][6610][6611][6612][6613] Additional Information: Abstract: A range of substituted dihydroisoquinolinium salts has been tested in the catalytic asymmetric epoxidation of simple alkenes using our newly developed non-aqueous conditions employing tetraphenylphosphonium mono-peroxysulfate (TPPP) as oxidant, giving ees of up to 97%.In 1976 it was established that oxaziridinium salts are extremely reactive reagents for oxygen transfer to nucleophilic substrates. 2 Since then, there has been significant interest in developing effective iminium salt catalysts for epoxidation of olefins. 3 The primary oxidant used is oxone, and the reactions are usually performed at 0 ºC in the presence of a base. In addition to an organic solvent, usually acetonitrile, water is an essential cosolvent, required in order to provide sufficient oxone solubility.We have previously described our approach to new types of cyclic chiral iminium salts, functionalized with chiral units at the nitrogen atom. 4 These enantiomerically pure iminium salts have been successfully employed in the catalytic asymmetric epoxidation of unfunctionalized alkenes, the dioxane-derived catalysts 1-5 giving ees of up to ca 60%, 5 catalyst 6 giving ees of up to 97%, 6 and catalyst 7 ees of up to 95%. The standard conditions employed by ourselves and others in epoxidation reactions catalysed by iminium salts involve the use of oxone as stoicheiometric oxidant, a base (2 mol eq of Na 2 CO 3 per eq of oxone) and water / acetonitrile as solvent mixture.The principal limitation of this system is the restricted range of temperatures at which the epoxidation can be performed (ca -5 °C to ambient). The upper temperature limit results from the relatively fast decomposition of oxone in basic media at room temperature. The lower limit is determined by the requirement for an aqueous solution (the normal ratio of solvents is (CH 3 CN:H 2 O; 1:1); aqueous acetonitrile freezes at -8 °C.An additional drawback arising from the dependency on oxone is the large quantity of inorganic salt byproducts produced in the reaction. We were pleased to find that the use of TPPP in place of oxone induces efficient epoxidation in organic solvents in the absence of water, and furthermore that the presence of base is now not required; indeed, addition of base actually suppresses the epoxidation process. Use of this oxidant also enables greater scope for reaction monitoring and analysis, as water is no longer required. Reactions can be carried out at low temperature, and, when carried out in deuteriated solvent, monitored by NMR spectroscopy. We describe herein the catalytic asymmetric epoxidation of several unfunctionalized alkenes using catalysts 2-6 under the new anhydrous conditions, employing (TPPP) as stoichieometric oxidant. The catalysts were first tested in the asymmetric epoxidation of 1-phenycyclohexene at varying temperatures using TPPP in dichloromet...

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Designing New Chiral Ketone Catalysts. Asymmetric Epoxidation of cis-Olefins and Terminal Olefins

Cited by 123 publications

References 29 publications

Highly enantioselective epoxidation of styrenes: Implication of an electronic effect on the competition between spiro and planar transition states

Highly enantioselective epoxidation of styrenes: Implication of an electronic effect on the competition between spiro and planar transition states

Three‐Membered Heterocycles. Structure and Reactivity

Non-aqueous iminium salt mediated catalytic asymmetric epoxidation

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