Synthesis of sterically congested double helicene by alkyne cycloisomerization.

Alkyne cycloisomerization of 2,7,10,15-tetra( ortho -alkynylphenyl)benzo[ g , p ]chrysene containing bulky 4-alkoxy-2,6-dimethylphenyl groups at the alkyne terminals selectively proceeded at the sterically crowded bay-region. The obtained double helicene adopts a distorted structure with a high racemization barrier due to the intramolecular steric repulsion.