Conformation Analyses, Dynamic Behavior and Amide Bond Distortions of Medium-sized Heterocycles. 1. Partially and Fully Reduced 1-Benzazepines

Five 1-benzazepine heterocycles were synthesized by utilizing transition-metal-catalyzed processes in key bond-forming steps. <i>exo</i>-Methylene and methyl substituents were introduced at position 5, as well as a unit of unsaturation between positions 3 and 4, with benzoyl or benzyl <i>N</i>-substituents. Solution- and solid-state structures were examined, using dynamic NMR spectroscopy and X-ray crystallography, corroborated by molecular mechanics calculations. Greater amide distortion is associated with a more stable ground-state structure, which is in turn more reluctant to undergo conformational changes.