A drastic increase in the rate of racemization is found for the bridged hexahelicenophanes 1 (n=8, 10) relative to the unsubstituted parent [6]helicene. This unexpected result occurs from steric interactions between the polymethylenedioxy chains and the terminal rings, which causes the energy of the ground state to be raised and that of the transition state to be lowered.

C2‐Symmetric hexahelicenes 3a–3g, which bear four or six alkoxy chains, were prepared in eight‐to‐nine reaction steps in high overall yields. The final step consisted of a twofold oxidative photocyclization of the corresponding 2,7‐bis(2‐phenylethenyl)naphthalenes. Long (and branched) chains provide a good solubility and processability, which is a prerequisite for applications in organic synthesis and materials science.

The crystal structures of the [6]helicenes 4,13-(1,10-decamethylenedioxy)hexahelicene, C 36 H 34 O 2 , (I), and 4,13-(1,8octamethylenedioxy)hexahelicene, C 34 H 30 O 2 , (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) A Ê , respectively. The increased steric energy of the ground state is responsible for a signi®cantly lower racemization barrier of (I) and (II) in comparison to the unsubstituted [6]helicene. CommentRecently, we succeeded in the preparation of hexahelicenophanes (Meier et al., 1998) that have polymethylenedioxy chains between positions 4 and 13 in the terminal benzene rings A and F. It turned out that the racemization barriers ÁG À of (I) and (II) at 473 K in 1,2,4-trichlorobenzene are 8.6 and 19.0 kJ mol À1 , respectively, lower than in the parent compound [6]helicene. This surprising result must be due to the special geometrical effects of the bridges.

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