Vibrational CD study on the solution phase structures of the MacMillan catalyst and its corresponding iminium ion
Tino P Golub1, Christian Merten1
1Ruhr-Universität Bochum, Fakultät für Chemie und Biochemie, Organische Chemie II, Universitätsstraße 150, 44801 Bochum, Germany. christian.merten@ruhr-uni-bochum.de.
Physical Chemistry Chemical Physics : PCCP
|November 3, 2021
Summary
Vibrational circular dichroism (VCD) spectroscopy reveals the dominant "Houk-conformer" of MacMillan
Area of Science:
- Organic Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- MacMillan's imidazolidinone catalyst is crucial in asymmetric synthesis.
- Understanding the conformational preferences of intermediates is key to reaction optimization.
Purpose of the Study:
- To investigate the conformational preferences of iminium ions derived from MacMillan's catalyst using VCD spectroscopy.
- To demonstrate VCD spectroscopy's utility in determining dominant solution-phase conformations.
Main Methods:
- Experimental VCD spectroscopy of isolated and in situ generated iminium ions.
- Comparison of experimental VCD spectra with computed spectra.
- Analysis of conformational preferences of the parent catalyst and its salts in different solvents.
Main Results:
- VCD spectroscopy confirmed conformer 2b (the "Houk-conformer") as the dominant structure of the iminium ion in solution.
- The study identified subtle conformational shifts induced by solvent and counter-anion interactions.
Conclusions:
- VCD spectroscopy provides direct and accessible insights into the conformational preferences of iminium ions.
- The method is sensitive to minor conformational changes influenced by the chemical environment.
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