A comparative study of dynamic NMR spectroscopy in analysis of selected N-alkyl-, N-acyl-, and halogenated cytisine derivatives

New halogenated derivatives of (-)-cytisine were synthesized: 3-bromo-N-acetylcytisine, 5-bromo-N-acetylcytisine, 3,5-dibromo-N-acetylcytisine, 3-iodo-N-acetylcytisine, 5-iodo-N-acetylcytisine, 3,5-diiodo-N-acetylcytisine. Their structures were established on the basis of their NMR spectra and X-ray diffraction method. The crystal structures confirmed the chair conformation of ring C, while in solution all these compounds are in cis–trans conformational equilibrium with ring C in chair and boat conformation. Additionally, the correct X-ray structure of N-benzylcytisine was resolved.