Conformational Analysis of Sulfur-Containing Heterocycles,Part I. Synthesis and Structural Determination of Diastereomerically Pure 4,6-Bis-(phenoxymethyl)-1,2,5-trithiepanes |
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Authors: | Heydenreich Matthias Koch Andreas Ristau Thomas Knoll Susanne Heinicke Jochen Sieler Joachim Niemitz Matthias Mühlstädt Manfred Kleinpeter Erich |
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Institution: | (1) Institut für Organische Cheroie und Struktur-analytik, Universität Potsdam, Potsdam, Germany;;(2) Fakultät für Chemie und Mineralogie, Universität Leipzig, Leipzig, Germany;(3) Department of Chemistry, University of Kuopio, Kuopio, Finland |
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Abstract: | Some diastereomerically pure 4,6-bis-(phenoxymethyl)-l,2,5-trithiepanes were synthesized and unambiguously assigned. Their conformational properties and dynamic behavior were investigated by various NMR spectroscopic methods and quantum-chemical calculations at the HF/6-31G* level. The ground states of these compounds proved to be twist-chairs. A ring interconversion can occur in the meso-isomers as well as in the (±)-isomers. This interconversion can be described as a simultaneous inversion of the disulfide bridge. In the case of the meso-isomers, both ground states are mirror images of each other and the transition state is a highly symmetrical chair. The barrier heights of interconversion were determined to be in the range of 50 kJ/mol by variable-temperature NMR measurements. The ground states as well as the transition state of the (±)-isomers were found to be nonsymmetrical. However, those dynamic processes that are fast with respect to the NMR time scale lead to averaged NMR spectra at room temperature. A further dynamic process found through the quantum-chemical calculations is a flapping of the meth-ylene groups of the rings. The energy barrier of this flapping was calculated to be very small (< 20 kJ/mol) and could not be observed by low-temperature NMR measurements. |
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Keywords: | 4 6-Bis-(phenoxymethyl)-1 2 5-trithiepanes variable-temperature NMR conformational analysis ring interconversion HF/6-31G* transition state |
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