Enantioselective [2 + 2 + 2] Cycloisomerization of Alkynes in the Synthesis of Helicenes: The Search for Effective Chiral Ligands.

In order to construct helicene backbones in nonracemic form under Ni(0) catalysis, a large collection of phosphorus ligands is tested to achieve an enantioselective cycloisomerization of aromatic triynes.