| Abstract
| - Structural features (orientation of the carboxyl group, ring puckering), electronic absorption, andcircular dichroism spectra of 4-alkyl- and 4-aryl-dihydropyrimidones 1−5 are calculated bysemiempirical (AM1, INDO/S), ab initio (HF/6-31G*, CIS/6-31G*, RPA/6-31G*), and densityfunctional theory (B3LYP/6-31G*) methods. These calculations allow an assignment of the absoluteconfiguration by comparison of simulated and experimental CD spectra. Although the ab initiomethods greatly overestimate electronic transition energies, the general appearance of theexperimental CD spectra is quite nicely reproduced by these calculations. Thus, comparison ofexperimental with calculated CD spectra is a reliable tool for the assignment of the absoluteconfiguration. For 4-methyl derivatives 1, the first enantiopure DHPM examples with no additionalaromatic substituent, the stereochemistry at C4 provided by the theoretical results is confirmedby X-ray structure determination of the diastereomeric salt 6. Additional support is the consistentHPLC elution order found for all investigated DHPMs on a cellulose-derived chiral stationary phase.
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