Conformation and Stereodynamics of Monodioxamethylene Calix[4]arene Derivatives

J. Org. Chem., 63 (12), 3866 -3874, 1998. jo9720602 S0022-3263(97)02060-4
Web Release Date: May 19, 1998

Conformation and Stereodynamics of Monodioxamethylene Calix[4]arene Derivatives

Jens Wöhnert, Jörg Brenn, Matthias Stoldt, Oleg Aleksiuk, Flavio Grynszpan, Iris Thondorf,* and Silvio E. Biali*

Department of Biochemistry/Biotechnology, Martin-Luther-University, D-06099 Halle, Germany, and Department of Organic Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Received November 10, 1997

Abstract:

Reaction of the monospirodienone derivative of p-tert-butylcalix[4]arene with methylene chloride/base in the presence of a phase transfer catalyst yielded the bridged monodioxamethylene derivative 6 which was characterized by X-ray crystallography. Treatment of 6 with NaBH₄ resulted in exo-reduction of the carbonyl group and afforded the spiro alcohol 7, which rearranged thermally to the monodioxamethylene bridged calix[4]arene 3. Calixarene 3 exists in solution (CD₂Cl₂, 198 K) in three different conformations (a cone form with the dioxocine unit in a distorted boat conformation, and cone and partial cone forms with a boat-chair arrangement of the dioxocine) which interconvert with barriers in the 13.5-14.3 kcal mol^-1 range. Molecular mechanics calculations indicate that the rate-limiting steps for the conformational interconversions of 3 involve transitions of the dioxocine subunit.

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