Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
| Autor: | Pavletta Shestakova, Georgi M. Dobrikov, Zhanina Petkova, Yana Nikolova |
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| Rok vydání: | 2021 |
| Předmět: |
In situ
asymmetric reduction borane complexes Organic Chemistry squaramides DOSY NMR Pharmaceutical Science Nuclear magnetic resonance spectroscopy Squaric acid Borane Asymmetric induction Combinatorial chemistry Article Analytical Chemistry Catalysis chiral aminoalcohols chemistry.chemical_compound QD241-441 chemistry Chemistry (miscellaneous) Drug Discovery Molecular Medicine Physical and Theoretical Chemistry |
| Zdroj: | Molecules, Vol 26, Iss 6865, p 6865 (2021) Molecules Volume 26 Issue 22 |
| ISSN: | 1420-3049 |
| Popis: | A series of squaric acid amides (synthesized in 66–99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH3•SMe2. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% ee), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by 1H DOSY and multinuclear 1D and 2D (1H, 10/11B, 13C, 15N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of α-chloroacetophenone. |
| Databáze: | OpenAIRE |
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