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The reaction of enamines 4a, b with acrylonitrile gave rise to compounds 6a, b in addition to four ( 7a–10a and 7b–10b ) stereoisomeric derivatives of a new heterocyclic ring system, the structures of which were thoroughly investigated by different spectroscopic methods, in particular by C NMR. Molecular structures of 7a–10a were substantiated by single crystal X-ray diffraction. Crystal data were collected on a CAD-4 diffractometer using monochromatic CuKα radiation (λ = 1.541 80 A) and the model structures determined by direct methods were refined on F 2 values. The conformations of the four diastereomeric molecules are rather similar. The epimerization at C(12) has only a slight effect on the bond angles around the bridge head atom, while the exchange of the -C 2 H 5 and -C 2 H 4 CN functions has practically no impact on the bond lengths, bond angles and torsion angles around C(1). The excellent internal consistency of the molecular geometry permitted characterization of the bond lengths of C(sp 3 )-X (X  C(sp 3 ), C(aryl), C(sp), etc.) types.