High Diastereoselection of a Dissymmetric Capsule by Chiral Guest Complexation

• Published in: Angewandte Chemie International Edition Vol. 53; no. 28; pp. 7243 - 7247
• Main Authors: Tsunoda, Yuta, Fukuta, Katsunori, Imamura, Taisuke, Sekiya, Ryo, Furuyama, Taniyuki, Kobayashi, Nagao, Haino, Takeharu
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 07.07.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: chirality; Complexation; diastereoselectivity; Dichroism; Encapsulation; Esters; Excitation; Helicity; Joining; Mathematical analysis; molecular recognition; Self assembly; stacking interactions; self-assembly; molecular recognition; diastereoselectivity; stacking interactions; chirality
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201403721

Encapsulation of chiral guests in the dissymmetric capsule 1⋅4 BF4 formed diastereomeric supramolecular complexes G⊂1⋅4 BF4 (G: guest). When chiral guests 2 a–q were encapsulated within the dissymmetric space of the self‐assembled capsule 1⋅4 BF4, circular dichroism (CD) was observed at the absorption bands that are characteristic of the π–π* transition of the bipyridine moiety of the capsule, which suggests that the P and M helicities of the capsule are biased by the chiral guest complexation. The P helicity of diastereomeric complex (S)‐2 l⊂1⋅4 BF4 was determined to be predominant, based on CD exciton coupling theory and DFT calculations. The diastereoselectivity was highly influenced by the ester substituents, such that benzyl ester moieties were good for improving the diastereoselectivity. A diastereomeric excess of 98 % was achieved upon the complexation of 2 j. The relative enthalpic and entropic components for the distereoselectivity were obtained from a van’t Hoff plot. The enthalpic components were linearly correlated with the substituent Hammett parameters (σp+). The electron‐rich benzyl ester moieties generated donor–acceptor π–π stacking interactions with the bipyridine moiety, which resulted in a significant difference in energy between the predominant and subordinate diastereomeric complexes. Guests in a twist: Coordination‐driven self‐assembly of an achiral cavitand produced a dissymmetric capsule. Interconversion of the P and M helicities of the capsule was biased by the encapsulation of a chiral guest with remarkable diastereoselectivity. The absolute helicity of the diastereomeric complex was determined based on CD exciton coupling theory and DFT calculations.