Electron‐Rich Cavitands via Fourfold Sonogashira Cross‐Coupling Reaction of Calix[4]arenes and Bromopyridines – Effect of the Nitrogen Position on Complexation Abilities

The fourfold Sonogashira cross‐coupling reaction is described as efficient synthetic tool for the preparation of calixarenes with relatively deep electron‐rich cavities. Reactions of halocalixarenes with terminal alkynes led to coupling products in yields up to 95 %. Two synthetic pathways to the tetraethynylcalixarene 5 were elaborated and their efficencies were compared. This calixarene was used for the synthesis of the three isomeric tetrakis(pyridylethynyl) compounds 10a–c, which were tested as hosts for the binding of pyridinium salts by mass spectrometric and 1H NMR examinations. The effect of the nitrogen position of the host systems revealed an interesting result: calixarene 3 (phenyl), 10a (2‐pyridyl), and 10c (4‐pyridyl) were able to bind NMP+ inside the cavity, calixarene 10b (3‐pyridyl) was not. Association constants were estimated for the complexes in CDCl3/CD3CN (9:1). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)