Konformationsanalysen von pyrolytisch erzeugten [2.2]phanen des 4‐Pyranons

Conformational Analyses of [2.2]Phanes of 4‐Pyranone Generated by Pyrolysis The synthesis of the first phanes of 4‐pyranone is accomplished by pyrolysis of bis(sulfone) 4 . Analogously, 9, 10 and 11 are synthesized. While 5 is conformationally mobile in solution, 9 and 10 are fixed (up to 100°C) and exhibit anti conformation as shown by X‐ray structural analysis ( 11 ). Like 9 and 11, 5 , exists in a staircase‐like structure in the crystal. 1 H‐NMR spectra of the metaparacyclophane 10 shows coalescence of the signals of the methylene protons at room temperature. The flexibility at 10 at 60°C is interpreted as a swinging process. The crystal structure of bis(sulfone) 8a shows that the two planar rings are tilted by 60°C with respect to each other.