STEREOCHEMISTRY AND CHIROPTICAL SPECTRA OF 3-AZABICYCLO[3.1.0]HEXAN-2-ONES AND THIONES

Several optically active substituted 3-azabicyclo[3.1.0]hexan-2-ones a nd their thiocarbonyl analogues have been synthesized, and their circu lar dichroism spectra studied. The crystal structure of thiolactam 1a showed that the bicyclic skeleton of the title compounds assumes a sof a-like geometry. It is postulated that the cyclopropyl moiety and amid e or thioamide group constitute an inherently chiral chromophore, heli city of which determines the Cotton effect sign corresponding to the n -pi electronic transition. The weak pi-pi* Cotton effect of thiolacta ms shows opposite sign to that observed for the lowest energy excitati on. (C) 1997 Elsevier Science Ltd.