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

Hickey, Matthew S.; Goeddel, David V.; Crane, Zackary D.; Shi, Yian

doi:10.1073/pnas.0307548101

Cited by 54 publications

(25 citation statements)

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“…Further studies show that a carbocylic analog of ketone 44a provides higher ees for styrenes (89-93% ee) than 44a [25]. The replacement of the pyranose oxygen with a less electronegative carbon raises the energy of the nonbonding orbital of the dioxirane and consequently enhances the stabilizing interaction of the nonbonding orbital of the dioxirane with the p Ã orbital of the alkene, thus further favoring the spiro transition state over the planar one [25].…”

Section: Catalyst Developmentmentioning

confidence: 96%

“…It appears that the stereodifferentiation for cis and terminal alkenes with 44a probably results from an apparent attractive interaction between the R p group of the alkene and the oxazolidinone moiety of the ketone catalyst in spiro transition state C (Figure 3.2) [24a -c]. Further studies show that a carbocylic analog of ketone 44a provides higher ees for styrenes (89-93% ee) than 44a [25]. The replacement of the pyranose oxygen with a less electronegative carbon raises the energy of the nonbonding orbital of the dioxirane and consequently enhances the stabilizing interaction of the nonbonding orbital of the dioxirane with the p Ã orbital of the alkene, thus further favoring the spiro transition state over the planar one [25].…”

Section: Catalyst Developmentmentioning

confidence: 99%

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Organocatalytic Oxidation. Ketone‐Catalyzed Asymmetric Epoxidation of Alkenes and Synthetic Applications

Shi

2010

Modern Oxidation Methods

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The asymmetric epoxidation of alkenes constitutes a powerful approach to enantiomerically enriched epoxides, a class of highly versatile intermediates in organic synthesis [1]. Various effective epoxidation systems have been developed, including epoxidation of allylic [2, 3] and homoallylic [4] alcohols, metal-catalyzed epoxidation of unfunctionalized alkenes [5][6][7], and the nucleophilic epoxidation of electron-deficient alkenes [8]. During the past 10-15 years, much effort has been devoted to chiral ketone-catalyzed asymmetric epoxidation (Scheme 3.1). The subject has been described in great detail in the first edition [9] and other reviews [10]. This chapter provides an update on progress in this area since the first edition [9].Scheme 3.1 Chiral ketone-catalyzed asymmetric epoxidation of alkenes.Modern Oxidation Methods. Edited by Jan-Erling Bäckvall

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Section: Catalyst Developmentmentioning

confidence: 96%

Section: Catalyst Developmentmentioning

confidence: 99%

Organocatalytic Oxidation. Ketone‐Catalyzed Asymmetric Epoxidation of Alkenes and Synthetic Applications

Shi

2010

Modern Oxidation Methods

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“…The reaction of styrene with ketone 32 gave styrene oxide with 81% ee, in contrast to 24% ee with ketone 31 (Scheme 11.41 ). A carbocyclic analogue 33 and N -aryl -substituted variants 34 are also introduced for styrene derivatives and cis -disubstituted olefi ns [72,73] . In addition, chiral ketone 35 bearing electron -withdrawing acetate groups was found to be active enough to promote the epoxidation of α , β -unsaturated esters, and the epoxy esters were obtained in a high yield with high enantioselectivity [74] .…”

Section: Organocatalystmentioning

confidence: 99%

Asymmetric Oxidations and Related Reactions

Matsumoto

Katsuki

2010

Catalytic Asymmetric Synthesis

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GENERAL INTRODUCTIONOxidation is a fundamental technology for converting bulk chemicals into valuable materials and is also a useful tool for sophisticated functionalization of organic molecules. Thus, intensive research efforts have been devoted to the development of selective and practical oxidation methods, and a wide variety of chiral metal -based catalysts and organocatalysts have been developed for catalytic asymmetric oxidation reactions in industry and academia in the last half -century [1] . In contrast to the rapid improvement in stereoselectivity, the enhancement of atom economy [2] falls behind. While atom effi ciency (especially active oxygen content in oxygenation reactions) of stoichiometric oxidants is a factor that should be considered, most of the catalytic asymmetric oxidations still use conventional stoichiometric oxidants of low atomeffi ciency such as peracids, alkyl hydroperoxides, hypervalent iodine reagents, hypochlorite, and N -oxide compounds (Table 11.1 ). The use of such oxidants causes the formation of large amounts of undesirable waste. From the viewpoint of ecological sustainability, oxidation with a higher atom -effi cient, safe, abundant, and preferably inexpensive oxidant is favorable. Considering the requirements, molecular oxygen and hydrogen peroxide are the oxidants of choice [3] . Molecular oxygen offers a large advantage because it is abundant in air and is inexpensive. Aerobic oxidation that directly uses ambient air as an oxidant is similar to respiration in living organisms. Hydrogen peroxide is also recognized as a green oxidant. It is almost as equally atomeffi cient as molecular oxygen, and the by -product is safe and clean water. Moreover, its aqueous solution (typically 30 -35%) is inexpensive and easy to handle. Consequently, the development of catalytic asymmetric oxidations with molecular oxygen Catalytic Asymmetric Synthesis, Third Edition, Edited by Iwao Ojima

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“…Noteworthy the epoxysilanes were effectively desilylated by TBAF to give the corresponding styrene oxide derivatives without erosion of the enantioselectivity. [11] A combination of TiA C H T U N G T R E N N U N G (OiPr) 4 and salan ligand 2 was also effective for the epoxidation. [12] In the reaction of dimethylphenylA C H T U N G T R E N N U N G (styryl)silane, the epoxysilane was obtained in 59 % with > 99 % ee (Scheme 1).…”

mentioning

confidence: 98%

“…[1][2][3] However, there are no satisfactory methods available thus far for the asymmetric epoxidation of terminal olefins such as styrene. [4] While epoxysilanes are a synthetic equivalent of epoxides, a highly enantioselective epoxidation of simple alkenylsilanes is also quite rare in the literature. [5,6] Although Shi and co-workers applied their sugar-derived ketone catalyst to the epoxidation of 2,2-disubstituted alkenylsilanes and obtained the epoxysilanes with high enantioselectivity up to 94 % ee, the method has a major drawback that it requires a substoichiometric amount of the catalyst.…”

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confidence: 99%

Highly Enantioselective Epoxidation of cis‐Alkenylsilanes

Matsumoto

Kubo

Katsuki

2009

Chemistry A European J

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Since the development of the titanium/tartrate-catalyzed asymmetric epoxidation of allyl alcohols in 1980, significant progress has been made in the field of asymmetric epoxidation of olefins, and now most olefins can be transformed to epoxides with high optical purity. [1][2][3] However, there are no satisfactory methods available thus far for the asymmetric epoxidation of terminal olefins such as styrene.[4] While epoxysilanes are a synthetic equivalent of epoxides, a highly enantioselective epoxidation of simple alkenylsilanes is also quite rare in the literature. [5, 6] Although Shi and co-workers applied their sugar-derived ketone catalyst to the epoxidation of 2,2-disubstituted alkenylsilanes and obtained the epoxysilanes with high enantioselectivity up to 94 % ee, the method has a major drawback that it requires a substoichiometric amount of the catalyst. [7,8] While the introduction of a sterically more demanding silyl group at the vinyl position is expected to further facilitate the enantioface-differentiation, there is a concern that the steric hindrance strongly inhibits the reaction progress.[5] Thus, in order to implement the catalytic asymmetric epoxidation of alkenylsilanes, the utilization of a more refined epoxidation catalyst in terms of catalytic activity, asymmetric induction and durability is necessary.We have reported that the di-m-oxo-TiA C H T U N G T R E N N U N G (salalen) complex 1 (Figure 1) is an effective catalyst for the asymmetric epoxidation of olefins with aqueous hydrogen peroxide as the oxidant.[9] Not only conjugate olefins but also non-conjugate olefins, which still are the most challenging substrate for asymmetric epoxidation with regard to both reactivity and enantioselectivity, underwent the epoxidation to give the epoxides with high enantioselectivity. Thus, we expected that TiA C H T U N G T R E N N U N G (salalen) 1 would best meet the requirements for the epoxidation of alkenylsilanes. Herein, we report the catalytic asymmetric epoxidation of cis-alkenylsilanes, in which the cis-epoxysilanes are obtained with complete enantioelectivity using 0.5-2 mol % of the catalyst.cis-Alkenylsilanes were readily prepared by simple reduction of the corresponding alkynylsilanes with diisobutylaluminum hydride.[10] We first examined the scope of alkenylsilanes in the presence of TiA C H T U N G T R E N N U N G (salalen) 1 (Table 1). The complex 1 effectively promoted the epoxidation of cis-alkenylsilanes bearing aromatic groups. Silicon substituents have little effect on the enantioselectivity (entries 1 and 2). The reactions furnished both the trimethylsilyl-and dimethylphenylsilyl epoxides with ee values of > 99 %. Substituted alkenylsilanes with electron-donating methoxy and electron-withdrawing bromide groups on the aromatic ring also underwent the epoxidation with complete enantioselectivity (entries 3-7). However, the substitution at the ortho-position decreased the reaction rate (entries 3 and 5). The reaction with methoxy group at this position required a longer reaction tim...

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

Cited by 54 publications

References 104 publications

Organocatalytic Oxidation. Ketone‐Catalyzed Asymmetric Epoxidation of Alkenes and Synthetic Applications

Organocatalytic Oxidation. Ketone‐Catalyzed Asymmetric Epoxidation of Alkenes and Synthetic Applications

Asymmetric Oxidations and Related Reactions

Highly Enantioselective Epoxidation of cis‐Alkenylsilanes

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