Study of Ground State Interactions of Enantiopure Chiral Quaternary Ammonium Salts and Amides,Nitroalkanes, Nitroalkenes,Esters, Heterocycles,Ketones and Fluoroamides |
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Authors: | Grazia Bencivenni Dr Diana Salazar Illera Dr Maria Moccia Prof K N Houk Dr Joseph A Izzo Dr Johanna Novacek Prof Paolo Grieco Prof Mathew J Vetticatt Prof Mario Waser Prof Mauro F A Adamo |
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Institution: | 1. Department of Chemistry, RCSI, University of Medicine and Health Science, 123 St Stephen's Green, Dublin 2, Dublin, Republic of Ireland;2. CNR-ICC, Institute of Crystallography, Via G. Amendola 122/O, 70126 Bari, Italy;3. Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095-1569 USA;4. Department of Chemistry, State University of NY Binghamton, Binghamton, NY, USA;5. Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstrasse 69, 4040 Linz, Austria;6. Faculty of Pharmacy, University of Naples Federico II, Corso Umberto I, 40, 80138 Napoli, NA, Italy |
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Abstract: | Chiral phase-transfer catalysis provides high level of enantiocontrol, however no experimental data showed the interaction of catalysts and substrates. 1H NMR titration was carried out on Cinchona and Maruoka ammonium bromides vs. nitro, carbonyl, heterocycles, and N−F containing compounds. It was found that neutral organic species and quaternary ammonium salts interacted via an ensemble of catalyst +N−C−H and (sp2)C−H, specific for each substrate studied. The correspondent BArF salts interacted with carbonyls via a diverse set of +N−C−H and (sp2)C−H compared to bromides. This data suggests that BArF ammonium salts may display a different enantioselectivity profile. Although not providing quantitative data for the affinity constants, the data reported proofs that chiral ammonium salts coordinate with substrates, prior to transition state, through specific C−H positions in their structures, providing a new rational to rationalize the origin of enantioselectivity in their catalyses. |
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Keywords: | heterocycles hydrogen bonds NMR spectroscopy organocatalysis phase-transfer catalysis |
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