Twisted Baskets

• Published in: Chemistry : a European journal 2015-02, Vol.21 (9), p.3550-3555
• Main Authors: Hermann, Keith, Pratumyot, Yaowalak, Polen, Shane, Hardin, Alex M., Dalkilic, Erdin, Dastan, Arif, Badjić, Jovica D.
• Format: Article
• Language: English
• Subjects: Baskets; Catalysis; cavitands; Chemistry; encapsulation; Fluorescence; host-guest systems; Inclusions; Magnetic Resonance Spectroscopy; Menthol; Models, Molecular; Modular; Molecular Structure; Naphthalene; Naphthalenes - chemistry; Quantum Theory; Spectroscopy; Spectrum analysis; Stereoisomerism; stereoselective recognition; supramolecular chirality; Titanium - chemistry; Transesterification
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201406492

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)‐1syn) or left ((M)‐1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)‐1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)‐1syn is accomplished by its transesterification with (1R,2S,5R)‐(−)‐menthol in the presence of a TiIV catalyst to give diastereomeric 8P and 8M. It was found that dendritic‐like cavitands 8P and 8M, in CD2Cl2, undergo self‐inclusion (1H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was (1H NMR spectroscopy) found to be greater in the case of 8P than 8M. Accordingly, it is suggested that different folding characteristic of 8P and 8M ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8P/8M, encompassing right‐ and left‐handed “cups”, was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8P/8M. Diving in: A preparative procedure for obtaining a pair of novel twisted baskets is presented. The resolution of this modular yet racemic host is completed with the assistance of a menthol auxiliary, which acts as a guest penetrating one of the hosts to a greater degree. Having useful chiroptical characteristics and chiral inner space, twisted baskets hold promise for application in the areas of sensing, drug purification and supramolecular catalysis (see figure).