Ye B, Cramer N * Ecole Polytechnic Fédérale de Lausanne, Switzerland
Chiral Cyclopentadienyl Ligands as Stereocontrolling Element in Asymmetric C–H Functionalization.
Science 2012;
338: 504−506
Key words
rhodium - chiral cyclopentadienyl ligands - isoquinolones - asymmetric C–H functionalization
Significance
A rhodium complex with a chiral Cp ligand that catalyzes an enantioselective synthesis
of isoquinolones via a directed C–H bond functionalization is reported. Often, in
half-sandwich transition-metal-catalyzed reactions, Cp remains the sole permanent
ligand on the metal. Thus, despite the challenges, the development of chiral Cp ligands
for inducing enantioselectivity is a powerful approach.
Comment
The highly effective Cp ligand reported is postulated to control the spatial orientation
of the coupling partners. For instance, the ligand is C
2-symmetric to avoid diastereomeric coordination of the metal. The benzophenone ketal
shields one face of the substrate and the equatorial methyl group pushes the bulky
Boc group away. The controlled trajectory of the attacking alkene gives rise to the
stereo-configuration of the product.
