High-pressure synthesis, structures, and conformational properties of some derivatives of 7-azabicyclo[2.2.1] heptane. X-Ray determination of endo-10-benzoyl-4-phenyl-4,10-diazatricyclo[5.2.1.0]dec-8-ene-3,5-dione and exo-10-acetyl-4-phenyl-4,10-diazatricyclo[5.2.1.0]decane-3,5-dione
The syntheses, using pressures of up to 1.4 GPa, and the properties of Diels–Alder adducts of some N-acylated pyrroles are described. Both exo and endo adducts may be obtained and purified and are, in general, unstable with respect to the retro reaction. Progress towards a general synthesis of the 7-azabicyclo[2.2.1]heptane system is described. Structures of two of the adducts, those between N-phenylmaleimide (2b) and N-benzoylpyrrole (1a) and the dihydro adduct of (2b) with N-acetylpyrrole (1b), have been determined by X-ray crystallographic analysis. Examination of these structures by means of 1H n.m.r. temperature-dependent spectra and nuclear Overhauser effect differences confirm that conformational isomerism is due to restricted rotation about the amide C–N bond, the energy barrier, 70 kJ mol–1, being similar to that in acyclic amides.