Non-biaryl atropisomers derived from carbohydrates. Part 3: Rotational isomerism of sterically hindered heteroaryl imidazolidine-2-ones and 2-thiones

The present work describes in detail the preparation and structural characterization of a series of heteroaryls in which an o,o′-disubstituted phenyl ring is connected through a single C–N bond to a heterocyclic fragment of a chiral imidazolidine-2-one or 2-thione. As a consequence of hindered rotation, some of these substances exist as stable rotamers at room temperature and can easily be separated and characterized. Molecular mechanic calculations have also been carried out to evaluate the barriers to rotation.