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Partially hydroxy depleted calix 4 arenes

, : Partially hydroxy depleted calix 4 arenes. Journal of Organic Chemistry 56(2): 532-536

The partially OH depleted dihydroxy- and trihydroxycalix[4]arenes 2 and 3 were synthesized in order to assess the relative importance of the cyclic hydrogen bond on the conformation of p-tert-butylcalix[4]arene. Both compounds were prepared from the same diethyl diphosphate ester precursor under different reductive cleavage conditions. The ring inversion barriers of 2 and 3 are < 10 and 11.6 kcal mol-1, respectively. The completely OH depleted calixarene 5 and the MeOH solvate of dihydroxylcalixarene 2 exist in the crystal in a 1,2-alternate conformation. Trihydroxycalixarene 3 crystallizes as a 1:2 pyridine solvate in which 3 adopts a cone conformation. One pyridine molecule is hydrogen bonded to one OH group o 3, while simultaneously being included into the cavity of another molecule of 3. It is concluded that three phenolic units are sufficient to stabilize the cone conformation.


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