Chiroptical Properties and Conformation of 4,5-Saturated Derivatives of 5-Aryl-l,4-benzodiazepin-2-ones

CD spectra of a series of 5-aryl-7-chloro-l,3,4,5-tetrahydro2H-l,4-benzodiazepin-2-one derivatives having different substituents at positions 1, 3, 4, and 5 were studied. The absolute eonfiguration at C-5 of two homochiral analogues, 1 and 2, having enantiomorphous ring conformations was determined on the basis of chiroptical correlations and theoretical calculations. The latter have shown that the optical activity mainly originates from the one-electron mechanism and is determined by the helicity of the diazepine ring, i. e. by the inherent chirality of the partial chromophore 4-chloro-N,2-dimethyl-formanilide. Exciton inter action s between transitions of the two arornatic chromophores A and C also give a significant contribution to chiroptical properties. By applying simple chiroptical rules dedueed from experimental spectra and supported by calculations, the stereochemistry (absolute conformation and configuration), of 3,5-disubstituted cis and trans epimeric pairs (7-17) was revealed.