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High Diastereoselection of a Dissymmetric Capsule by Chiral Guest Complexation
Author(s) -
Tsunoda Yuta,
Fukuta Katsunori,
Imamura Taisuke,
Sekiya Ryo,
Furuyama Taniyuki,
Kobayashi Nagao,
Haino Takeharu
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201403721
Subject(s) - chemistry , diastereomer , moiety , substituent , supramolecular chemistry , stereochemistry , bipyridine , crystallography , circular dichroism , crystal structure
Encapsulation of chiral guests in the dissymmetric capsule 1⋅4 BF 4 formed diastereomeric supramolecular complexes G ⊂ 1⋅4 BF 4 ( G : guest). When chiral guests 2 a – q were encapsulated within the dissymmetric space of the self‐assembled capsule 1⋅4 BF 4 , 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 BF 4 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 (σ p + ). 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.