The Preparation and Crystal Structures of Octaoxoketocalix[8]arene Derivatives: The Ketocalixarene Counterparts of the Largest “Major” Calixarene

The purpose of this study was to synthesize and structurally characterize ketocalixarenes (i.e., calixarenes where the bridging methylene bridges are replaced by carbonyl groups) derived from the largest “major” calixarene, namely p-tert-butylcalix[8]arene 3a. Ketocalix[8]arenes were synthesized by the oxidation of protected p-tert-butylcalix[8]arene derivatives. Octamethoxy-p-tert-butylketocalix[8]arene 6b was prepared by the photochemical reaction of the calixarene 3b with NBS in a CHCl₃/H₂O mixture. The oxidation of the methylene groups of octaacetoxy-p-tert-butylcalix[8]arene 3c was conducted by a reaction with CrO₃ in Ac₂O/AcOH. The basic hydrolysis of the acetate groups of the oxidation product yielded octahydroxy-p-tert-butylketocalix[8]arene 6a. In the crystal, the molecule adopts a saddle-like conformation of crystallographic C₂ and idealized S₄ symmetry. Strikingly, the array of OH/OH intramolecular hydrogen bonds present in the parent 3a is completely disrupted in 6a.