Atropisomerism in hindered naphthyl sulfones

The existence of asymmetric conformations, leading to a pair of conformational enantiomers, has been observed by variable temperature NMR in hindered naphthyl sulfones, either monitoring the signals of prochiral groups or the signals of non-prochiral groups in a chiral environment. The corresponding enantiomerization barriers were determined by line shape analysis. In a sulfone featuring two stereogenic axes, the presence of both meso and racemic conformers has been detected and, by means of an appropriately cooled (-80 degrees C) enantioselective column, the three expected conformational stereoisomers have been physically separated, allowing assignment of the meso structure to the most stable species. MM calculations were also employed to describe the stereodynamic processes.