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 --butylcalix[8]arene .

Conformationally restricted calix[8]arenes substituted at all methylene bridges.

Reaction under S(N)1 conditions of the octabromocalix[8]arene derivative 2d with alcohols proceeds in nonstereoselective fashion, but all-cis octaryl derivatives are the single major products in the reaction with arenes. The incorporation of aryl substituents at the bridges rigidifies the calix[8]arene skeleton.

Incorporation of substituents at the methylene linkages of the Calix[5]arene skeleton.

Under S(N)1 reaction conditions, the bromine atoms of the pentabromo p-tert-butylcalix[5]arene 6 were replaced by alkoxy, electron-rich aryl, and acetylacetonate groups.

Functionalization of the methylene bridges of the calix[6]arene scaffold.

The bromine atoms of the hexabromo calixarene derivative 3 were replaced by other groups under S(N)1 conditions, allowing the facile synthesis of calix[6]arene derivatives incorporating identical functionalities at all bridges. Heating at reflux a mixture of 3 and the appropriate alcohol incorporated primary and secondary alkoxy substituents. Hydride abstraction was observed when the reaction with EtOH and i-PrOH was conducted in hexafluoroisopropanol (HFIP).

Intramolecular SNAr reactions in a large-ring ketocalix[6]arene.

Ketocalix[6]arene 2e was prepared by CrO3 oxidation of the methylene groups of 2a, followed by hydrolysis of the acetate groups. 2e undergoes intramolecular SNAr reactions under the usual methylation conditions (MeI, base), yielding mono- and dixanthone calixarene derivatives.