Asymmetric catalytic Pauson–Khand reactions with chiral phosphine ligands: Dramatic effects of substituents in 1,6-enyne systems

A cobalt-catalyzed reaction of 1,6-enyne systems under a carbon monoxide atmosphere using chiral phosphine ligands provides a facile entry to optically active 2-cyclopentenone derivatives. (S)-BINAP was demonstrated to be the most effective in the cobalt-catalyzed cyclization of 1,6-enynes among various chiral bidentate phosphine ligands employed, affording chiral 2-cyclopentenone derivatives with high enantioselectivity. The dramatic effects of the substituents in the 1,6-enynes were observed in this asymmetric synthesis. A plausible mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained.