Chiral Cationic (CpRu)-Ru-x(II) Complexes for Enantioselective Yne-Enone Cyclizations
The cydopentadienyl (Cp) group is a ligand of great importance for many transition-metal complexes used in catalysis. Cationic CpRuII complexes with three free coordination sites are highly versatile catalysts for many atom-economic transformations. We report the synthesis of a family of (CpRuII)-Ru-x complexes with chiral Cp ligands keeping the maximum number of available coordination sites. The cationic members are efficient and selective catalysts for yne-enone cyclizations via formal hetero-Diels-Alder reactions. The transformation proceeds in <1 h at -20 degrees C and provides pyrans in up to 99:1 er. Unsaturated ester or Weinrebamide substrates directly yield the iridoid skeleton.