Double-two-point and four-point intramolecular bridging of p-tert-butylcalix[8]arene

Calix[8]arenes bis-bridged at the lower rim with ortho- or meta-xylene unit (3a-b and 4a-b) have been obtained in high yields by reaction of 1,3,5,7-tetra-O-substituted calix[8]arenes with 1,2- or 1,3-bis(bromomethyl)benzene. The use of 1,2,4,5-tetrakis(bromomethyl)benzene afforded the four-point intrabridged calix[8]arenes 5a-b in yields up to 41%. VT NMR studies indicated that the flipping motion of aromatic rings in these compounds is inhibited by the intramolecular bridging. Molecular modeling suggested an unprecedented pseudo pleated loop conformation for compounds 5a-b.