Chiral Cationic Cp(x)Ru(II) Complexes for Enantioselective Yne-Enone Cyclizations.

The cyclopentadienyl (Cp) group is a ligand of great importance for many transition-metal complexes used in catalysis. Cationic CpRu(II) complexes with three free coordination sites are highly versatile catalysts for many atom-economic transformations. We report the synthesis of a family of Cp(x)Ru(II) 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 °C and provides pyrans in up to 99:1 er. Unsaturated ester or Weinreb-amide substrates directly yield the iridoid skeleton.