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Pseudotetrahedral polyhaloadamantanes as chirality probes: synthesis, separation, and absolute configuration
Peter R Schreiner1, Andrey A Fokin, Oliver Lauenstein
1Institut für Organische Chemie der Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany. prs@chem.uga.edu
Journal of the American Chemical Society
|November 7, 2002
Summary
Researchers synthesized novel halogenated adamantanes using phase-transfer catalysis. The study demonstrates a powerful combination of experimental and theoretical methods for assigning absolute configurations, even in complex molecules.
Area of Science:
- Organic Chemistry
- Stereochemistry
- Spectroscopy
Background:
- Stable, chiral halogenated hydrocarbons are valuable synthetic targets.
- Assigning absolute configurations of complex molecules can be challenging.
Purpose of the Study:
- To synthesize novel conformationally and configurationally stable halogenated adamantanes.
- To separate and determine the absolute configurations of these compounds.
- To showcase the utility of combined experimental and computational methods for stereochemical assignment.
Main Methods:
- Phase-transfer catalytic halogenation for synthesis.
- High-Performance Liquid Chromatography (HPLC) on chiral stationary phases for enantiomeric separation.
- Circular Dichroism (CD) spectroscopy (experimental and computed) for absolute configuration determination.
- Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray crystallography for structural elucidation.
Main Results:
- Successfully synthesized 1-bromo-3-chloro-5-fluoro-adamantane and 1-bromo-3-chloro-5-fluoro-7-iodoadamantane.
- Achieved >99% enantiomeric excess (ee) for the optical antipodes of 1-bromo-3-chloro-5-fluoro-adamantane.
- 1-bromo-3-chloro-5-fluoro-7-iodoadamantane represents the first chiral aliphatic hydrocarbon containing all stable halogens.
- Confirmed structures using NMR and X-ray crystallography.
- Demonstrated successful absolute configuration assignment using CD spectroscopy, even for molecules with weak optical rotation and lacking typical chromophores.
Conclusions:
- Phase-transfer catalysis is an effective method for preparing complex halogenated adamantanes.
- Chiral HPLC and CD spectroscopy are powerful tools for enantiomeric separation and absolute configuration assignment.
- The combination of experimental data and theoretical calculations provides robust stereochemical determination for challenging molecules.
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