Calix [4] arene scaffold based quaternary ammonium salts as multi-site phase transfer catalysts were prepared and their catalytic activities were investigated for Darzens condensation, O/N-alkylation reactions and ethyl benzene oxidation. These calix [4] arene based multi-site phase transfer catalysts showed significant high catalytic activity as compared to single-site phase transfer catalysts.
[Murray, Robert W.; Shiang, Dawn L. Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1972-1999), 1990 , # 2 p. 349 - 352]