Stereochemistry of N-formyl-cis-2,4-diaryl-3-azabicyclo[3.3.1]nonanes

Four N-formyl-cis-2,4-diaryl-3-azabicyclo[3.3.1]nanones 5-8 have been prepa red and their preferred conformations determined using NMR: spectral studie s, X-ray crystallography and semiempirical calculations (AM1 and PM3 of MOP AC 6). They all prefer twin-chair conformation with a nearly coplanar; N-CH O function with reference to the C2-N3-C4 plane. X-Ray analysis of a single crystal of 6 shows that there are two; independent molecules in the asymme tric unit, the overall conformation being the same in both the molecules of the asymmetric unit. Employing variable temperature NMR studies, the barri er for N-C rotation in the N-formylazabicyclo[3.3.1]nonane 6 has been found to be 58.25 kJ/mol.