RESTRICTED ROTATION INVOLVING THE TETRAHEDRAL CARBON .63. ENDEAVOR TOWARD ENHANCING THE ROTATIONAL BARRIER IN 9-S-ALKYLTRIPTYCENES

In order to enhance barriers to rotation about the C-9-substituent bon d in 9-s-alkyltritpycenes the secondary alkyl group was modified as we ll as the peri-substituent. The barrier was slightly enhanced by modif ying the substituents but the extent was rather limited. This limitati on was attributed to the limitation of the ways of preparation of 9-s- alkyltriptycenes that should give three stable rotamers and carry subs tituents at peri-positions, where only 1,8-difluoro substituents could be used.