Enantiopure Double Rosettes

Exploiting the same concept, Reinhoudt and Shinkai were able to obtain another example of enantioenriched chiral double-rosette made of achiral components. In this case achiral calix[4]arene bearing dimelamine moieties with pyridine functionalities were assembled with achiral cyanurate leading to racemic chiral double rosettes. The latter are perfect counterparts for chiral D-dibenzoyl tartaric acid via two-point hydrogen-bonding interactions thus 

The imbalance between the two diastereoisomers is prolonged when the chiral D-tartrate is removed by precipitation with ethylendiamine thus leading to an enantioenriched chiral double-rosette made of achiral components with 90% e.e. The memory effect in this case is even stronger then in the former example with activation energy towards racemization as high as 119 KJ/mol and a half-life time of one week at room temperature. 

---

Fig. 8 Schematic representation of highly diastereoselective non-covalent synthesis achiral dimelamine calix[4]arene with enantiopure chiral cyanurate components lead to chiral double rosettes with d.e. as high as 96% (R)-cyanurate induces complete (P) chirality, while (S) favors only (M) chirality...

---