conformation of syn-5,13-dimethyl[2.2]metacyclophane was established by X-ray crystallographic analysis, and its steric energy evaluated by MM2 calculations. Based on these data the steric strain inherited in the compound was concluded to originate mainly from the nearly eclipsed conformation of two ethano bridges.

5-Formyl-13-methyl- and 5,13-diformyl-syn[2.2]metacyclophanes were synthesized. Their electronic spectra, ΔH≠ for their benzene ring flipping, and the result of molecular orbital calculations were compared with those of the 5,13-dimethyl derivative, with the conclusion that Coulombic repulsion between two benzene rings is the major factor controlling the stability of syn conformers.

The title compound was synthesized in 3 steps from trithia[23](1,3,5)cyclophane. Activation parameters for its change to the anti conformer as well as its NMR, IR and UV spectra were secured.

AbstractAus dem bekannten Trithia‐cyclophan (I) erhält man bei Einwirkung von Butyllithium Gemische der Dithiole (II), die bei der Photolyse mit Trimethylphosphit zu den Verbindungen (III)‐(V) entschwefelt werden.