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 at mosphere using chiral phosphine ligands provides a facile entry to opticall y active 2-cyclopentenone derivatives. (S)-BINAP was demonstrated to be the most effective in the cobalt-catalyzed cyclization of 1,6-enynes among var ious chiral bidentate phosphine ligands employed, affording chiral 2-cyclop entenone derivatives with high enantioselectivity. The dramatic effects of the substituents in the 1,6-enynes were observed in this asymmetric synthes is. A plausible mechanism for the asymmetric induction is proposed on the b asis of the stereochemical outcome obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.