FORMATION OF THE 1,3,5,7-TETRAMETHYL ETHER IN THE WEAK-BASE-CATALYZED METHYLATION OF P-TERT-BUTYLCALIX[8]ARENE

The previously unreported 1,3,5,7-tetramethoxy-p-tert-butylcalix[8] (2) has been obtained as an insoluble material through a protection-deprotection procedure by subjecting the known 1,3,5,7-tetrakis(p-tert-butylbenzyl) ether (3) to methylation (NaH/THF-DMF) followed by debenzylation (Me(3)SiBr/CHCl3). Compound 2 is insoluble in most common organic solvents and was characterized through alkylation with p-bromobenzyl bromide to give the mixed octasubstituted compound (5) with alternate methoxy and p-bromobenzyloxy groups in the macrocycle. In the light of this result, a reinvestigation of methylation of p-tert-butylcalix[8]arene (1) promoted by weak bases was undertaken. In order to overcome insolubility problems, the crude reaction mixture was subjected to exhaustive benzylation that yielded the soluble mixed methyl-benzyl ethers; It was thus evidenced that direct 1,3,5,7-tetramethylation occurs and this clarifies the apparently ''anomalous'' behaviour of MeI with respect to other electrophiles.