Tetramethoxy-p-tert-butylcalix[4]arene (1  ) was deprotonated with n-butyllithium then treated with a geminal dihalide (CH2ClI or PhCHBr2) to give corresponding 2-(a-chloroalkyl)calix[4]arene 2  and 2-(a-bromobenzyl)calix[4]arene 3  . These species underwent base-promoted dehydrohalogenation to yield 2-methylenetetramethoxy-p-tert-butylcalix[4]arene (4  ) and 2-(phenylmethylene)tetramethoxy-p-tert-butylcalix[4]arene (5  ). The alkene calixarenes 4  and 5  were demethylated at the lower rim by hydrogen iodide generated in situ by thermal decomposition of iodocyclohexane to form 2-methylenetetrahydroxy-p-tert-butylcalix[4]arene (6  ) and 2-(phenylmethylene)tetrahydroxy-p-tert-butylcalix[4]arene (7  ). A 2-(bromomethylene)calixarene (8  ) is formed from addition of Br2 to 4  followed by spontaneous loss of HBr. The tetrahydroxy species 6  , 7  , and 8  each assume a cone conformation in solution (CDCl3) as judged by 1H NMR spectra. The barrier to cone�cone inversion was determined by analysis of variable-temperature 1H NMR spectra, demonstrating that the presence of a methylene substituent lowers the activation barrier by ca. 2 kcal/mol. Substituents on the methylene group increase the activation barrier.

Synthesis and solution structural characterization of 2-methylenetetrahydroxy-<i>p</i>-<i>tert</i>-butylcalix[4]arene and its derivatives

247th National Meeting (2014)

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Synthesis and solution structural characterization of 2-methylenetetrahydroxy-p-tert-butylcalix[4]arene and its derivatives