Conformational behavior of dithia[n.3.3](1,3,5)cyclophanes and dithia[n.3.3](1,2,6)cyclophanes

The conformational behavior of a series of crown-fused dithia[n.3.3](1,2,6)cyclophanes () and dithia[n.3.3](1,3,5)cyclophanes () was investigated by variable-temperature 1H and 13C NMR spectroscopy, X-ray crystallography and density functional theory (DFT) calculations. Single crystal X-ray structure analysis showed that two thia-bridges in adopted a pseudochair–pseudochair (cc) conformation and the cyclophane decks underwent a ring-tilting motion in the case of [10.3.3](1,2,6)cyclophane (). In contrast, the thia-bridges in took both cc and pseudoboat–pseudochair (bc) conformations, and the ring-tilting process was also found in [10.3.3](1,3,5)cyclophane (). Variable temperature 1H NMR study revealed that there was no wobbling-motion for two thia-bridges in while thia-bridges in experienced a wobbling-process with a conformational barrier of 9.21 and 8.80 kcal mol−1, respectively, for and [13.3.3](1,3,5)cyclophane (). DFT calculations for the two cyclophanes series revealed that preferred a cc conformation which was consistent with the experimental observation; similarly, took a preferential cc conformation, agreeing with having a predominant cc conformer (cc:bc ratio=70:30), but not having a predominant bc conformer (cc:bc ratio=15:85) in the solid state.