Chiral bicyclo[3.3.1]-3,7-dioxanonane derivatives: Study of crystallization mode and conformational dynamics in solution

A homologous series of chiral bis-ketals and mixed hemiketal-ketals with rigid bicyclo[3.3.1]-3,7-dioxanonane skeleton has been prepared. The crystallization mode (conglomerate or racemic compound) was established by chiral HPLC with double UV/polarimetric detection. The study of the solid-state structure by single crystal X-ray diffraction disclosed interesting CH⋯π intermolecular interactions. Hindering of rotation of phenyl groups at (hemi)ketalic centres was found to occur. A 1H–DNMR study gave activation barriers Δ G # of 15.9 kcal mol−1 in the ketalic moiety and 10.3 kcal mol−1 in the hemiketalic moiety. The experimental results were substantiated by MM and DFT calculations for ground and transition states.