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

Abstract

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.