0000000000177689
AUTHOR
Manfred Schwertel
ChemInform Abstract: 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) A, 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.
ChemInform Abstract: Synthesis of Highly Substituted Hexahelicenes
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.
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) A, 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.