Rotaxanes with dynamic mechanical chirality: Systematic studies on synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion

Strategies for the Synthesis of Mechanically Planar Chiral Rotaxanes

Rotaxanes, belonging to the class of classical mechanically interlocked molecules (MIMs), exhibit chiral properties that diverge from those of traditional chiral elements, particularly displaying mechanically planar chirality. Their distinctive spatial structure further augments their chiral significance, thereby imparting them with vast potential for applications in the realm of chiral materials and asymmetric catalysis. In recent years, mechanically planar chiral rotaxanes have garnered increasing attention from researchers. In this review, we summarize the recent advancements in obtaining enantiopure mechanically planar chiral rotaxanes. In this regard, chiral separation techniques, the use of chiral auxiliaries, and asymmetric catalytic synthesis have emerged as potent methodologies for constructing chiral rotaxanes, thereby enabling the synthesis of diverse types of mechanically planar chiral rotaxanes. Additionally, we analyze the current challenges faced in this field and look forward to the future development opportunities that lie ahead.

Synthesis of 'Impossible' Rotaxanes

'Impossible' rotaxanes, which are constituted by interlocked components without obvious binding motifs, have attracted the interest of the mechanically interlocked molecules (MIMs) community. Within the synthetic efforts reported in the last decades towards the preparation of MIMs, some innovative protocols for accessing 'impossible' rotaxanes have been developed. This short review highlights different selected synthetic examples of 'impossible' rotaxanes, as well as suggests some future directions of this research area.