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.