jo010491l_si_001.pdf (1.04 MB)
Absolute Configuration in 4-Alkyl- and 4-Aryl-3,4-dihydro-2(1H)-pyrimidones: A Combined Theoretical and Experimental Investigation
journal contribution
posted on 2001-09-01, 00:00 authored by Georg Uray, Petra Verdino, Ferdinand Belaj, C. Oliver Kappe, Walter M. F. FabianStructural features (orientation of the carboxyl group, ring puckering), electronic absorption, and
circular dichroism spectra of 4-alkyl- and 4-aryl-dihydropyrimidones 1−5 are calculated by
semiempirical (AM1, INDO/S), ab initio (HF/6-31G*, CIS/6-31G*, RPA/6-31G*), and density
functional theory (B3LYP/6-31G*) methods. These calculations allow an assignment of the absolute
configuration by comparison of simulated and experimental CD spectra. Although the ab initio
methods greatly overestimate electronic transition energies, the general appearance of the
experimental CD spectra is quite nicely reproduced by these calculations. Thus, comparison of
experimental with calculated CD spectra is a reliable tool for the assignment of the absolute
configuration. For 4-methyl derivatives 1, the first enantiopure DHPM examples with no additional
aromatic substituent, the stereochemistry at C4 provided by the theoretical results is confirmed
by X-ray structure determination of the diastereomeric salt 6. Additional support is the consistent
HPLC elution order found for all investigated DHPMs on a cellulose-derived chiral stationary phase.