Phosphine-substrate recognition through the C-H...O hydrogen bond: application to the asymmetric Pauson-Khand reaction.
A unique methine moiety attached to three heteroatoms (O, P, S) and contained in the PuPHOS and CamPHOS ligands serves as a strong hydrogen-bond donor. Nonclassical hydrogen bonding of this methine with an amido-carbonyl acceptor provides a completely diastereoselective ligand exchange process between an alkyne dicobalthexacarbonyl complex and a phosphine ligand. This weak contact has been studied by means of X-ray analysis, 1H NMR, and quantum mechanical calculations and revealed that the present interaction falls in the range of strong C-H...O=C bonds. The hydrogen-bond bias obtained in the ligand exchange process has been exploited in the asymmetric intermolecular Pauson-Khand reaction to yield the corresponding cyclization adducts in up to 94% ee.
Solà
Jordi
J
Unitat de Recerca en Síntesi Asimètrica (URSA-PCB), Parc Científic de Barcelona and Departament de Química Orgànica, Universitat de Barcelona, c/Josep Samitier, 1-5, E-08028 Barcelona, Spain.
Riera
Antoni
A
Verdaguer
Xavier
X
Maestro
Miguel A
MA