CIRCULAR-DICHROISM OF AXIALLY CHIRAL METHAQUALONE, 3-ARYL-2-MERCAPTO-4(3H)-QUINAZOLINONES AND 3-ARYL-2-ALKYLTHIO-4(3H)-QUINAZOLINONES - CONFORMATIONAL DEPENDENCE OF CD AND ASSIGNMENT OF ABSOLUTE-CONFIGURATION

Rotational strengths calculated on the basis of quantum-mechanically o btained minimum energy geometries were used to determine the absolute configurations of axially chiral 3-aryl-4 (3H)-quinazolinones from the sign of the observed Cotton effects (CEs). For the spectral data, CND O/S calculations were used; for the geometries, ab initio (RHF/6-31G) and semiempirical (AM1) theories were used. Oscillator and rotational strengths of all excited states down to 200 nm were compared to experi mental absorption and circular dichroism (CD) data. It was found that the sign of the L-1(b) Cotton effects obtained for the enantiomers of methaqualone and derivatives of 3-aryl-2-alkylthio-4 (3H)-quinazolinon es can be correlated unambiguously with the absolute configuration. Fu rthermore, the sign of the Cotton effect of the pi-pi transition of t he thiocarbonyl chromophore of 3-aryl-2-mercapto-4 (3H)-quinazolinones is suitable for a successful stereochemical correlation. (C) 1998 Wil ey-Liss, Inc.