Narrow-Rim Functionalization of Calix[4]arenes via Sonogashira Coupling Reactions

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Abstract
The narrow (or “lower”)-rim hydroxyl groups of calixarenes are known to be resistant to substitution/displacement. The Sonogashira coupling reaction with TMSA and phenylacetylene, however, has now been extended to the bistriflate of p-tert-butylcalix[4]arene, previously known to be resistant to Stille, Neigishi, or Suzuki−Miyaura reactions. Under some of the reaction conditions investigated, the previously unknown narrow-rim mono- and diiodo-p-tert-butylcalix[4]arene products were also produced, in addition to the narrow-rim mono- and dialkynyl products. Homocoupling of the narrow-rim monoethynyl-p-tert-butyl-calix[4]arene produced a new narrow-rim rigid butadiyne-linked bis-p-tert-butylcalix[4]arene.