| 1. |
- Aplander, Karolina, et al.
(författare)
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Asymmetric Lewis Acid Catalysis in Water: alpha-Amino Acids as Effective Ligands in Aqueous Biphasic Catalytic Michael Additions
- 2009
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :6, s. 810-821
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Tidskriftsartikel (refereegranskat)abstract
- This article explores the potential of native a-amino acids as chiral ligands in aqueous asymmetric Lewis acid catalysis, employing the C-C bond forming Michael addition as a model reaction. Some insights are provided regarding the details of Yb(OTf)(3)/alpha-amino acid-catalyzed Michael additions in water through new kinetic data as well as studies on how both yield and selectivity are influenced by variations in metal/ligand ratio, pH, temperature, and structure of the a-amino acid, Through this investigation it was found that reaction conditions that require only 5 mol-% of the Lewis acid, provides enantiomeric excesses of up to 79 % and is applicable to a wider range of donors and acceptors than previously demonstrated. Importantly, it was also demonstrated that the a-amino acid complexed ytterbium. catalyst might have potential for large-scale applications as it displays not only large ligand accelerations, but also good solubility and stability in water. It can be recycled multiple times without appreciable loss of activity. The result is a promising example of a water-compatible chiral Lewis acid. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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| 2. |
- Grintsevich, Sergey, et al.
(författare)
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An Alternative Approach to the Hydrated Imidazoline Ring Expansion (HIRE) of Diarene-Fused [1.4]Oxazepines
- 2020
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Ingår i: European Journal of Organic Chemistry. - : WILEY-V C H VERLAG GMBH. - 1434-193X .- 1099-0690. ; 2020:35, s. 5664-5676
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Tidskriftsartikel (refereegranskat)abstract
- A four-step approach to the "hydrated imidazoline ring expansion" (HIRE) is presented. In most cases, the ring expansion was the sole process. However, for the first time, an alternative course of the hydrated imidazoline evolution was discovered which gaveN-aminoethyl derivatives. These can, in principle, be converted into the target HIRE products under sufficiently forcing conditions. The approach offers improved flexibility with respect to the peripheral substituents and is also applicable to the synthesis of eleven-membered lactams. We observed that the latter can exist in two stable isomeric forms due to lactam-amide bond isomerization. The latter finding further demonstrates the value of medium-sized rings as multiple-conformer probes for biological target interrogation.
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| 3. |
- Reutskaya, Elena, et al.
(författare)
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Sulfur Oxidation Increases the Rate of HIRE-Type [1.4]Thiazepinone Ring Expansion and Influences the Conformation of a Medium-Sized Heterocyclic Scaffold
- 2021
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 86:8, s. 5778-5791
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Tidskriftsartikel (refereegranskat)abstract
- The hydrated imidazoline ring expansion (HIRE-type) reaction was investigated for a series of di(hetero)arene-fused [1.4]thiazepinones in comparison with their sulfone counterparts. The sulfones were found to undergo ring expansion at a much higher rate compared to the thioethers, much in line with the current mechanistic understanding of the process. Moreover, the amide bond cis- and trans-isomers of the ring-expanded products were found, in the case of sulfones, to be stabilized through an intramolecular hydrogen bond. The latter phenomenon was studied in detail by NMR experiments and corroborated by X-ray crystallographic information.
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