Silica Sulfuric Acid-Catalyzed Syntheses of Calix[4] Resorcinarenes

Analysis by RP-HPLC and Purification by RP-SPE of the C-Tetra(p-hydroxyphenyl)resorcinolarene Crown and Chair Stereoisomers

“…Of these isomers, the crown stereoisomer is the thermodynamically stable compound; alternatively, the structure of resorcinarenes can be rigidified into a crown by linking the hydroxyl groups of the upper rim, which provides a higher degree of preorganization. Resorcinarenes with substituted methylene bridge are found in crown structure in the crystal state [17–19], and in solution, the isomer may adopt crown and chair structures [20, 21]; however, the chair structure can interconvert in the crown structure at high-temperature conditions in the presence of highly polluting metal catalysts [22, 23].…”