Asymmetric Organocatalytic Epoxidation of α,β‐Unsaturated Aldehydes with Hydrogen Peroxide.

Marigo, Mauro; Franzén, Johan; Poulsen, Thomas B.; Zhuang, Wei; Joergensen, Karl Anker

doi:10.1002/chin.200539090

Cited by 14 publications

(18 citation statements)

References 5 publications

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“…68 Consequently, an incoming nucleophile would be directed to the lower Si face of the transient Eiminium chain. 69 To validate this reversible conformational strategy to facilitate enantioinduction in a catalysis setting, the epoxidation of enals using hydrogen peroxide 70 was explored (Figure 10). The commercial catalyst 71 (10 mol % loading) was employed in CHCl 3 as reaction medium at ambient temperature with hydrogen peroxide as the oxidant.…”

Section: Fluorine Stereoelectronic Control In Iminium Ion Organocatal...mentioning

confidence: 99%

Informing Molecular Design by Stereoelectronic Theory: The Fluorine Gauche Effect in Catalysis

2018

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The axioms of stereoelectronic theory constitute an atlas to navigate the contours of molecular space. All too rarely lauded, the advent and development of stereoelectronic theory has been one of organic chemistry's greatest triumphs. Inevitably, however, in the absence of a comprehensive treatise, many of the field's pioneers do not receive the veneration that they merit. Rather their legacies are the stereoelectronic pillars that persist in teaching and research. This ubiquity continues to afford practitioners of organic chemistry with an abundance of opportunities for creative endeavor in reaction design, in conceiving novel activation modes, in preorganizing intermediates, or in stabilizing productive transition states and products. Antipodal to steric governance, which mitigates destabilizing nonbonding interactions, stereoelectronic control allows well-defined, often complementary, conformations to be populated. Indeed, the prevalence of stabilizing hyperconjugative interactions in biosynthetic processes renders this approach to molecular preorganization decidedly biomimetic and, by extension, expansive. In this Account, the evolution and application of a simple donor-acceptor model based on the fluorine gauche effect is delineated. Founded on reinforcing hyperconjugative interactions involving C(sp)-H bonding orbitals and C(sp)-X antibonding orbitals [σ → σ*], this general stratagem has been used in conjunction with an array of secondary noncovalent interactions to achieve acyclic conformational control (ACC) in structures of interest. These secondary effects range from 1,3-allylic strain (A) through to electrostatic charge-dipole and cation-π interactions. Synergy between these interactions ensures that rotation about strategic C(sp)-C(sp) bonds is subject to the stereoelectronic requirement for antiperiplanarity (180°). Logically, in a generic [X-CH-CH-Y] system (X, Y = electron withdrawing groups) conformations in which the two C(sp)-X bonds are synclinal (i.e., gauche) are significantly populated. As such, simple donor-acceptor models are didactically and predictively powerful in achieving topological preorganization. In the case of the gauche effect, the low steric demand of fluorine ensures that the remaining substituents at the C(sp) hybridized center are placed in a predictable area of molecular space: An exit vector analogy is thus appropriate. Furthermore, the intrinsic chemical stability of the C-F bond is advantageous, thus it may be considered as an inert conformational steering group: This juxtaposition of size and electronegativity renders fluorinated organic molecules unique among the organo-halogen series. Cognizant that the replacement of one fluorine atom in the difluoroethylene motif by another electron withdrawing group preserves the gauche conformation, it was reasoned that β-fluoroamines would be intriguing candidates for investigation. The burgeoning field of Lewis base catalysis, particularly via iminium ion activation, provided a timely platform from which to explore a postulated ...

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Section: Fluorine Stereoelectronic Control In Iminium Ion Organocatal...mentioning

confidence: 99%

Informing Molecular Design by Stereoelectronic Theory: The Fluorine Gauche Effect in Catalysis

2018

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“…Weitz−Scheffertype epoxidation, which is the common methodology for asymmetric epoxidation of enones, is not suitable because the β-carbon of the olefin is sterically protected and also because steric congestion between the β substituent and the carbonyl moiety promotes fast epimerization at this carbon after peroxide attack, producing diastereomeric mixtures. 5 Two previous successful examples operate in β-trifluoromethyl-β,βdisubstituted chalcones and rely on phase-transfer catalysts 6 (Scheme 1a). In this specific class of substrates, the electrophilicity of the olefin is accentuated by the strong electron-withdrawing character of the trifluoromethyl group.…”

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confidence: 99%

Enantioselective Epoxidation of β,β-Disubstituted Enamides with a Manganese Catalyst and Aqueous Hydrogen Peroxide

et al. 2019

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“…We then envisioned the use of an organocatalytic approach for the installation of the β ‐OH group and oxidation of the aldehyde to the ester . In the first step, a catalyst controlled asymmetric epoxidation was performed with the proline‐derived secondary amine catalysts B and C . Sterically demanding catalyst B resulted in good selectivity with moderate yield, whereas slightly diminished selectivity but good yield was obtained with biphenyl‐substituted catalyst C .…”

Section: Resultsmentioning

confidence: 99%

Allelopathic Activity of the Iron Chelator Anachelin – A Molecular Hybrid with a Dual Mode of Action

Sarkar

Blom

Bethuel

et al. 2016

Helvetica Chimica Acta

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One of the compounds suggested to be responsible for the cyanobacterial dominance over competing green algae is identified. Evidence is provided on the molecular, chemical level that the iron chelator anachelin from the cyanobacterium Anabaena cylindrica promotes both the growth of cyanobacteria and reduces the growth of competing chlorophytes. These results illustrate a molecular strategy of addressing two challenges (nutrient availability and algal competition) by one molecule. Such strategies could be implied in harmful algal blooms in marine and freshwater environments. Such strategies could be implied in harmful algal blooms in marine and freshwater environments.

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Asymmetric Organocatalytic Epoxidation of α,β‐Unsaturated Aldehydes with Hydrogen Peroxide.

Cited by 14 publications

References 5 publications

Informing Molecular Design by Stereoelectronic Theory: The Fluorine Gauche Effect in Catalysis

Informing Molecular Design by Stereoelectronic Theory: The Fluorine Gauche Effect in Catalysis

Enantioselective Epoxidation of β,β-Disubstituted Enamides with a Manganese Catalyst and Aqueous Hydrogen Peroxide

Allelopathic Activity of the Iron Chelator Anachelin – A Molecular Hybrid with a Dual Mode of Action

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