Enantioselective epoxidation of electron‐deficient olefins: an organocatalytic approach

The discovery of simple and efficient catalyst systems for the asymmetric oxofunctionalization of hydrocarbons is a challenging task of catalytic chemistry. In this paper, we give an overview of catalyst systems capable of conducting asymmetric oxygenative transformations of organic molecules and, in line with the major trend to sustainability, relying on green oxidants HO and O as the ultimate oxygen source. The full historical period of asymmetric oxidation catalysis (1970 to the present day) is covered; both transition-metal-based and organocatalytic systems are considered. The focus of this review is the catalytic properties of the existing catalyst systems, in particular stereoselectivity, activity, efficiency, and synthetic outlook. At the same time, mechanistic peculiarities of stereoselective oxygen transfer are given attention.

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“…This section will provide a brief overview of the above catalyst systems. More detailed considerations can be found in refs , , and − .…”

Section: Asymmetric Epoxidation Reactionsmentioning

confidence: 99%

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H₂O₂and O₂

2017

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“…Phase-transfer catalysis is a highly beneficial technique; in particular, for industries, this technique permits the use of inexpensive and less hazardous reactants and solvents under mild conditions in the organic procedures and provides a direct cost-effective conversion of the reactants to the products with increased selectivity . Out of these, the chiral PTCs have found extensive applications in asymmetric synthesis. , Several organic reactions are being carried out successfully with PTCs; these include (i) alkylation, ,,,− (ii) conjugate addition, − (iii) cyclization, − (iv) epoxidation, − (v) condensation, − and (vi) oxidation. − PTCs belonging to the NR 4 + X – class are being used more often in biphasic reaction media in the laboratory and industries. At industrial scales, the stability of NR 4 + -type PTCs is generally poor. , This factor restricts the use of these PTCs to some mild processes in the pharmaceutical and fine chemical industries, and only a handful of organic reactions such as N - and O -alkylation, , oxidation, , reduction, , and benzylation are being catalyzed by PTCs at the industrial scale.…”

Section: Introductionmentioning

confidence: 99%

NL₂⁺ Systems as New-Generation Phase-Transfer Catalysts

2018

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Phase-transfer catalysts (PTCs), currently, are one of the most important tools of chemists for performing organic reactions. PTCs accelerate several types of reactions in biphasic systems, giving excellent yields of the desired product. Most of the PTCs belong to the general formula NRX. In the recent past, several compounds possessing a novel scaffold with the general formula NLX have been reported as PTCs. In the NL species, a nitrogen atom with a formal positive charge accepts electron density from electron-donating ligands. Electronic structure studies reported in the literature confirmed the possibility of L → N coordination (donor-acceptor) interactions in these species, and thus, this class of compounds are known as divalent N compounds. These species are reported to exhibit better catalytic potential in comparison to the traditional NR systems. Some of the NL systems are found to be useful in asymmetric phase-transfer catalysis. Thus, these systems offer extensive opportunities for exploring the catalytic properties and novel mechanistic aspects associated with their unique electronic structure. In this paper, the synthesis, electronic, and structural properties and the applications in catalysis of the NL-based PTCs are reviewed with their bright future scope in catalytic organic chemistry.

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“…Asymmetric epoxidations of electron-deficient olefins have recently attracted wide attention, because the resulting optically active epoxides are valuable precursors of many biologically active organic compounds (Scheme ). − Existing catalytic approaches, exploiting either metal-based catalysts or organocatalysts, ,,− are mostly focused on the epoxidation of α,β-unsaturated ketones, while efficient general catalytic methods for the enantioselective epoxidation of other types of olefins containing electron-withdrawing groups remain less developed.…”

Section: Introductionmentioning

confidence: 99%

Highly Enantioselective Bioinspired Epoxidation of Electron-Deficient Olefins with H₂O₂on Aminopyridine Mn Catalysts

et al. 2014

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The asymmetric epoxidation of various electron-deficient olefins with H 2 O 2 in the presence of a novel family of chiral bioinspired bipyrrolidine-derived aminopyridine manganese(II) complexes [LM II (OTf) 2 ] is reported. High enantioselectivities (up to 99% ee) and epoxide selectivities (up to 100%), unprecedented for catalysts of this type, have been achieved; the catalysts perform up to 8500 catalytic turnovers. The presence of electron donors in the catalyst structure substantially enhances the enantioselectivity. Isotopic ( 18 O) labeling studies provide evidence of the formation of the oxomanganese(V) active species. Hammett analysis suggests that the enantioselective epoxidation is rate-limited by the transfer of an electron to the Mn V O intermediate, to form a short-lived acyclic (carbocationic) intermediate. In effect, the epoxide stereoconfiguration may be affected by the competition between the rotation around the C α −C β single bond and the epoxide ring collapse.

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Enantioselective epoxidation of electron‐deficient olefins: an organocatalytic approach

Cited by 56 publications

References 102 publications

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H₂O₂and O₂

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H₂O₂and O₂

NL₂⁺ Systems as New-Generation Phase-Transfer Catalysts

Highly Enantioselective Bioinspired Epoxidation of Electron-Deficient Olefins with H₂O₂on Aminopyridine Mn Catalysts

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Enantioselective epoxidation of electron‐deficient olefins: an organocatalytic approach

Cited by 56 publications

References 102 publications

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H2O2and O2

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H2O2and O2

NL2+ Systems as New-Generation Phase-Transfer Catalysts

Highly Enantioselective Bioinspired Epoxidation of Electron-Deficient Olefins with H2O2on Aminopyridine Mn Catalysts

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Product

Resources

About

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H₂O₂and O₂

Catalytic Asymmetric Oxygenations with the Environmentally Benign Oxidants H₂O₂and O₂

NL₂⁺ Systems as New-Generation Phase-Transfer Catalysts

Highly Enantioselective Bioinspired Epoxidation of Electron-Deficient Olefins with H₂O₂on Aminopyridine Mn Catalysts