Asymmetric Epoxidation Catalyzed by N-Aryl-Substituted Oxazolidinone-Containing Ketones:  Further Evidence for Electronic Effects

Shu, Lianhe; Wang, Pingzhen; Gan, Yonghong; Shi, Yian

doi:10.1021/ol020229e

Cited by 85 publications

(34 citation statements)

References 10 publications

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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%

“…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.…”

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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%

mentioning

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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“…Since it is well known that sugar-derived dioxiranes are excellent organic catalysts for the enantioselective epoxidation of alkenes, [66] several experiments were carried out with the aim of anchoring precatalyst 21 ( Figure 8) on MeOPEG 5000 by using the phenol oxygen as connecting element. [67] This support was considerd particularly convenient considering that the epoxidation reaction is carried out in a solvent mixture perfectly suitable for the use of PEG.…”

Section: Ketonesmentioning

confidence: 99%

Immobilization of Organic Catalysts: When, Why, and How

2006

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This review article is divided in two parts. In the first part (Sections 2 and 3) selected examples of the publications that appeared in the literature in the period 2003–2005 in the field of immobilized organic catalysis are presented. When appropriate, the results of these publications are compared to those reported earlier and already discussed in a previous review article (see ref. 4). On the basis of this survey, in Section 4 some general considerations about when and why a supported version of an organic catalyst is worth developing are proposed. In Section 4 a list of suggestions about how the process of immobilization should be carried out is also included, taking into account several factors such as the properties of the catalyst, the nature of the support, and the mode of connection of the catalyst to the support.

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“…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. In studies involving the epoxidation of cis-methylstyrene (317), the electronic character of the oxazolidino N-aryl group was found to influence the outcome of the reaction, presumably by modulating the interaction between the catalyst and the aromatic substituent of the substrate [364]. Similarly, increasing the steric demand adjacent to the amide carbonyl can improve selectivity [365].…”

Section: Using Dioxiranesmentioning

confidence: 99%

Three‐Membered Heterocycles. Structure and Reactivity

Murphree

2011

Modern Heterocyclic Chemistry

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Asymmetric Epoxidation Catalyzed by N-Aryl-Substituted Oxazolidinone-Containing Ketones: Further Evidence for Electronic Effects

Cited by 85 publications

References 10 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

Immobilization of Organic Catalysts: When, Why, and How

Three‐Membered Heterocycles. Structure and Reactivity

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