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)naphthalenometacyclophane 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.