The syn conformers of several 2,11-dithia[3.3](1,4)naphthalenometacyclophanes: novel preference for a conformation with parallel benzenoid rings from direct confrontation of two different modes of non-bonding interaction

Abstract

2,11-Dithia[3.3](1,4)naphtha lenometacyclophane and its 9-bromo- and 9-fluoro-derivative have been synthesized. ¹H and ¹⁹F n.m.r. studies have indicated that all three dithiacyclophanes prefer the syn-conformation with near-parallel stacking of aromatic rings. This conformational preference is supported by results from MMP₂ calculations. The angle of tilting of the meta-bridged ring is dependent on the 9-substituent. Variable-temperature n.m.r. studies have unexpectedly shown neither a flipping of the meta-bridged ring nor a wobbling of the C–S–C bridges. Possible conformational behaviour is the continuous tilting process of the meta-bridged ring in the rigid syn-. conformation. A solvent effect on the chemical shifts of both the reference protons and the fluorine has been observed.