ALKYLATION PRODUCTS OF A CALIX[8]ARENE TRIANION - EFFECT OF CHARGE REDISTRIBUTION IN INTERMEDIATES

The behavior of a well-defined calin[8]arene trianion under alkylation conditions was investigated by reacting the tetraethylammonium salt o f p-tert-butylcalix[8]arene trianion with p-methylbenzyl bromide. Chro matography of the reaction mixture afforded the following derivatives in order of decreasing yields: 1,3,5,7-tetrakis-, 1,3-bis-, 1,3,5-tris -, 1,2,4-tris-, and mono(p-methylbenzyl)-p-tert-butylcalix[8]arene, be sides trace amounts of 1,4- and 1,5-disubstituted compounds. Comparabl e results were obtained using p-tert-butylbenzyl bromide. The observed regioselectivity has been explained by assuming that after each alkyl ation step the left negative charge is redistributed, by exchange equi libria, over the remaining phenolic groups with preferential localizat ion at those positions where contiguous H-bond stabilization is possib le and the electrostatic repulsion is minimized. The occurrence of pro tonation/deprotonation equilibria allows the formation of 1,3,5,7-tetr asubstituted calix[8]arene.