Having demonstrated the application of macrocycles (S)-1 in the synthesis of rotaxanes, we turned to their application in the synthesis of a mechanically planar chiral catenane (Figure ). Reaction of alkyne/azide pre-macrocycle 13 mediated by macrocycle (S)-1b under AT-CuAAC catenane forming conditions gave catenane 14 in moderate stereoselectivity (34% de). When macrocycle (S)-1e was used, corresponding catenane 15 was obtained as a single diastereomer (>96% de) as judged by 1 H NMR analysis of the crude reaction product and purified material. Pleasingly, a sample of rac-15, obtained by performing the same synthesis with rac-1e, produced crystals suitable for SCXRD analysis. The solid state structure obtained (Figure ), contained the rac-(S,Smp) diastereomer of catenane, which allows us to assign the product of the reaction with (S)-1e as (S,Smp)-15. Reduction of a sample of (S,Smp)-15 (>96% de) to give (S,Rmp)-14 (note the formal inversion of stereolabel, see ESI section S9), again as a single diastereomer as judged by 1 H NMR, allowed us to assign the major stereoisomer obtained using (S)-1b as (S,Rmp)-14. Thus, once again, macrocycles 1b and 1e are shown to form the mechanical bond with the same relative orientation of azide and alkyne components as for rotaxanes 4b-e. We initially intended to remove the chiral auxiliary from catenane 15 using the same sequence as for rotaxane 4e. However, fortuitously, we first attempted the same reaction with macrocycle (S)-1e using a CHCl3-EtOH solvent mix (1 : 1). Remarkably, we found that under these conditions, not only does mechanical bond formation proceed efficiently, but the auxiliary is also removed from the product to directly give catenane (Rmp)-16 in high stereoselectivity (>95% ee). Although extremely convenient, the process by which the auxiliary cleaves under these conditions is unclear. Attempts to apply this method in the case of macrocycle 1e alone or rotaxane 4e gave a complex mixture of products in which the desired cleavage product is a minor component (see ESI section S8). Nonetheless, these results demonstrate that macrocycle 1e can be used for the stereoselective synthesis of mechanically planar chiral catenanes. The auxiliary can then be removed either in a stepwise manner, as with rotaxane 4e, or in a single step under some circumstances, as here. [3]rotaxanes. In addition to being able to use macrocycle 1e to synthesise both mechanically planar chiral rotaxanes and catenanes in high enantiopurity, a particular advantage of placing the chiral auxiliary on the bipyridine macrocycle, rather than in alkyne or azide component, is that it is now possible to target more complicated chiral interlocked structures in a concise manner. In 1999, Vogtle and co-workers reported co-conformationally mechanically planar chiral [3]rotaxanes in which the axle component is bilaterally symmetric. Such molecules can be formed as either a pair of C2-symmetric enantiomers or as an achiral meso C2v diastereomer, depending on the relative orientation of the two rings (Figure ). Although Vogtle and co-workers were able to use CSP-HPLC to partially separate the mixture stereoisomers produced in an unselective manner, to our knowledge, this is the only reported example in which the mechanical bond provides the sole stereogenic unit. To address this unsolved challenge, we synthesised [3]rotaxanes 19 in a stepwise manner from bis-alkyne 17 via [2]rotaxane 18 using two sequential AT-CuAAC reactions. We envisaged we should obtain a chiral diastereomer by using the same stereoisomer of macrocycle 1e in both steps (i.e. (S)-1e [Figure ] or (R)-1e [not shown]) or the meso product if the first coupling was carried out with (S)-1e and the second with (R)-1e (not shown). In keeping with the results above, the stereoselectivity in the first AT-CuAAC step to give [2]rotaxanes 18 was high (96 : 4 de). Furthermore, SCXRD analysis of the carboxylic acid derivative of rotaxane 18 produced directly from (S)-1e (Figure ) allowed us to assign the absolute stereochemistry of the product as (S,Smp)-18. Reagents and conditions: i. (S)-1e (1 equiv.), 17 (1 equiv.), 3 (1 equiv.), [Cu(MeCN)4]PF6 (1 equiv.), i Pr2EtN (1 equiv.), CHCl3-EtOH (1 : 1), rt, 1 h. ii. TMSCHN2, THF-MeOH (1 : 1), rt, 18 h. iii. (S)-1e (1 equiv.), 3 (1 equiv.), [Cu(MeCN)4]PF6 (2 equiv.), i Pr2EtN (1 equiv.), CHCl3-EtOH (1 : 1), rt, 1 h. iv. LiAlH4, THF, 0 °C to rt, 4 h. v. (COCl)2, DMSO, NEt3, CH2Cl2, -78 C to rt. vi. piperidinium acetate, THF-H2O (9 : 1), 70 °C, 5 days.