DIRECT REGIOSELECTIVE FORMYLATION OF TETRAALKOXYCALIX[4]ARENES FIXED IN THE CONE CONFORMATION AND SYNTHESIS OF NEW CAVITANDS

Regioselectivity of the formylation of tetraalkoxycalix[4]arene fixed in the cone conformation has been studied. Direct, diametrical (1,3) diformylation of calix[4]arenes having four chelating chains at the lower rim has been achieved. Simple tetraalkoxycalix[4]arenes produce a mixture of diametrical (1,3) and proximal (1,2) diformylated products. The (1,3) functionalized compounds have been used for the synthesis of double calix[4]arenes 12a,d linked via the upper rim. The residual mobility of these cone conformers is indicated by the X-ray crystal structure of compound 12d, which shows a flattened cone conformation, and by the reactive behavior of 1,3-bis(hydroxymethyl) derivatives 9a,d which give very distorted 1,3-bridged compounds 11a,d, through an intramolecular cyclization process.