Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors.

Reactions between 1,8-dichloroanthracenes with substituents in position 10 and ortho -chloroaryne afford mixtures of 1,8,13- ( syn ) and 1,8,16-trichlorotriptycenes ( anti ). The syn / anti ratio is dependent on these substituents. Electropositive substituents like SiMe3 and GeMe3 lead to preferred formation of the syn -isomer, whereas CMe3 groups exclusively afford the anti -isomer. Different quantum chemical calculations including location of transition states give conflicting results, but indicate the importance of dispersion forces for an at least qualitative prediction of results. The syn -trichlorotriptycenes with SiMe3 and GeMe3 substituents were characterized by using NMR spectroscopy, mass spectrometry, and X-ray diffraction experiments.