Through-the-Annulus Threading of the Larger Calix[8]arene Macrocycle

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• 作者：Carmine Gaeta ; Carmen Talotta ; Luigi Margarucci ; Agostino Casapullo ; Placido Neri
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：August 2, 2013
• 年：2013
• 卷：78
• 期：15
• 页码：7627-7638
• 全文大小：747K
• 年卷期：v.78,no.15(August 2, 2013)
• ISSN：1520-6904

文摘

A complete study of the through-the-annulus threading of the larger calix[8]arene macrocycle with di-n-alkylammonium cations has been performed in the presence of the 鈥渟uperweak鈥?TFPB counterion. Thus, it was found that such threading occurs only upon partial preorganization of the calix[8]arene macroring by intramolecular bridging. In particular, 1,5-bridged calix[8]arenes with a meta- or para-xylylene bridge (2 and 3) gave pseudo[2]rotaxanes in which one dialkylammonium axle (4a鈥?b>4e⁺) was threaded into one of the two subcavities of the calix[8]-wheel. Conformational studies by using chemical shift surface maps and DFT calculations evidenced a 3/4-cone geometry for these subcavities. Higher pseudorotaxane K_ass values were obtained for calix[8]-wheels 2 and 3, with respect to calix[6]-host 1a, due to the cooperative effect of their two subcavities. Dynamic NMR studies on calix[8]-pseudorotaxanes evidenced a direct correlation between K_ass (and 螖G_ass) values and energy barriers for calix inversion due to the effectiveness of thread templation. In accordance with DFT calculations, an endo-alkyl preference, over the endo-benzyl one, was observed by threading calix[8]-wheel 3 with the directional n-butylbenzylammonium axle 4d⁺.