CALIXARENES .29. AROYLATION AND ARYLMETHYLATION OF CALIX[6]ARENES

Aroylations and arylmethylations of p-tert-butylcalix[6]arene have been carried out using a variety of parasubstituted aroyl chlorides and arylmethyl halides to determine the effect of para substituents on the structural and/or conformational outcome of the reactions. When an excess of derivatizing agent is used with NaH as the base the products in all cases are the 1,2,4,5-tetrasubstituted compounds in the 1,2,3-alternate conformation. However, with Me3SiOK as the base the products of arylmethylation are the 1,4-diethers. By varying the reaction conditions it is possible in some cases to prepare hexaethers as well as monoethers. By means of H-1 NMR spectral measurements it has been shown that any aroyl moiety or any para-substituted phenylmethyl moiety is large enough to prevent its rotation through the annulus of the calix[6]arene, thus partially, or in some cases completely, freezing the conformation. The unsubstituted benzyl moiety, however, is small enough to pass through the annulus fairly easily, thus allowing complete conformational interconversion to occur. The synthetic utility of these derivatives is adumbrated by the selective de-tert-butylation of a tetraester and the intramolecular bridging of a diether.