Restricted rotation of tert-butyl groups in sterically crowded methylene-functionalized calix[4]arenes

Organic Letters

Volumn 11, Issue 16, 2009, Pages 3662-3665

  Kuno, Lev ^a   Biali, Silvio E ^a  

^a HEBREW UNIVERSITY OF JERUSALEM   (Israel)

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Indexed keywords

EID: 68949115770     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol901472j     Document Type: Article

References (28)

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14. (a) For a recent report on the restricted rotation of t-Bu groups in hindered benzyl ethers, see: Casarini, D.; Coluccini, C.; Lunazzi, L.; Mazzanti, A. J. Org. Chem. 2006, 71, 4490.
15. (b) For a review, see: Oki, M. Applications of Dynamic NMR Spectroscopy to Organic Chemistry; VCH: Weinheim, 1985; p 255.
16. Simaan, S.; Biali, S. E. J. Org. Chem. 2003, 68, 7685.
17. For simplicity, we refer to compounds 4 and 5 as the di-tert-butyl and tri-tert-butyl derivatives, respectively, disregarding the four p-tert-butyl groups present at the upper rim of the calix scaffold.
18. In a related observation it has been reported that allyl ethers undergo cleavage in the presence of t-BuLi. (Bailey, W. F.; England, M. D.; Mealy, M. J.; Thongsornkleeb, C.; Teng, L. Org. Lett. 2000, 2, 489
19. For a review on ether cleavage see. Weissman, S. A.; Zewge, D. Tetrahedron 2005, 61, 7833.
20. Under the reaction conditions, the OH groups of 4 are deprotonated by the organolithium reagent, and the charge of the resulting phenolate is delocalized by the two ortho carbonyl groups. This delocalization decreases the electrophilicity of the carbonyl carbons, and may contribute to render them less susceptible to nucleophilic attack by the t-BuLi. In addition, agregation and intra- or intermolecular coordination of the lithium atoms with the oxygen atoms of the calix may also play a role in the decreased reactivity of 4.
21. Seri, N.; Biali, S. E. J. Org. Chem. 2005, 70, 5278.
22. Kuno, L.; Biali, S. E. J. Org. Chem. 2009, 74, 48.
23. gNMR V4.1.0; Cherwell Scientific Publishing: Oxford, U.K.
24. -1 has been estimated for the t-Bu rotation in a bicyclic system.
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