To follow up on this promising initial result, we explored the scope of the reaction with different 2-substituted quinolines (4a-f) (Table ). Both the reactivity and the enantioselectivity remained at the high level observed for the phenyl derivative when using more electron-donating or electron-withdrawing aromatic substituents (Table , entry 2-3). The same was found for the more sterically demanding biphenyl and t butyl substituents (Table , entry 4-5), indicating that the nanohoop catalyst does not increase enantioselectivity at the cost of a loss of activity for larger substrates. A reasonable explanation for this result is that the catalytic site in the macrocyclic catalyst is not confined in all three dimensions, but only in two. This reasoning is in agreement with what is known about the mechanism of the reaction, which features two consecutive hydrogenation events. Following the initial hydrogenation of the C-C bond, the subsequent hydrogenation of the C-N bond determines enantioselectivity. To achieve high ee, the Hantzsch ester needs to favour the Re or Si approach toward the complex of the substrate with the phosphate (Table ). It is plausible that the macrocyclic architecture allows enough space for the formation of this ternary complex between catalyst, substrate and Hantzsch ester, while offering a large difference between the Re and Si face due to its exceptionally high rigidity as well as secondary - interactions (Table ). In contrast to the wide scope observed for aryl groups, we found that the reactivity dropped drastically when subjecting 2-alkyl-substituted quinolines to transfer hydrogenation with our catalyst (Table , entry 6-7). Both 2-n-pentyl and 2-methyl quinolines reproducibly gave rise to sluggish reactivity and low levels of enantioselectivity, which is not the case for simple BINOL-based phosphoric acids, as reported previously by