Selective oxidation of thiacalix[4]arene (cone) to all corresponding sulfoxides

Abstract An upper rim unsubstituted thiacalix[4]arene immobilised in the cone conformation was regioselectively oxidized to give all possible sulfoxide isomers using NaBO 3 ·4H 2 O as the oxidizing reagent. Single crystal X-ray analysis undoubtedly assigned the stereochemistry of the sulfoxide group with the oxygen atom pointing toward the upper rim of the thiacalix[4]arene. As revealed by dynamic 1 H NMR, the presence of the sulfoxide groups has dramatic consequences on the conformational behavior of the thiacalix[4]arenes. Namely, that the number of sulfoxide groups is inversely proportional to the Δ G barrier of the pinched cone – pinched cone equilibrium as determined by Δ G values 45.4 kJ/mol for monosulfoxide 5 and Δ G 9 .