Alternatively, installing a facially symmetrical ring on one side of a prochiral center would give rise to a single co-conformational enantiomer (route b). Subsequent desymmetrisation of the faces of the ring would give rise to the same pair of diastereomers. Removal of the groups preventing co-conformational motion would give mechanically axially chiral enantiomers in which the mechanical bond provides the sole fixed source of stereochemistry. An advantage of this co-conformational chiral auxiliary approaches is that co-conformational enantiomers can be made using chiral pool starting materials by choosing where the mechanical bond is formed .