Two strained hexahelicenophanes

The crystal structures of the [6]­helicenes 4,13‐(1,10‐deca­methyl­ene­dioxy)­hexahelicene, C₃₆H₃₄O₂, (I), and 4,13‐(1,8‐octa­methyl­ene­dioxy)­hexahelicene, C₃₄H₃₀O₂, (II), show strong steric interactions between the terminal benzene rings and the poly­methyl­ene­dioxy chains. The shortest ring A and F distances amount to 2.941 (3) and 2.902 (3) Å, respectively. The increased steric energy of the ground state is responsible for a significantly lower racemization barrier of (I) and (II) in comparison to the unsubstituted [6]­helicene.