Catalytic Enantioselective Addition of Cyclic β-Keto Esters with Activated Olefins and N-Boc Imines Using Chiral <i>C</i><sub>2</sub>-Symmetric Cationic Pd<sup>2+</sup> N-Heterocyclic Carbene (NHC) Diaqua Complexes

2010-06-28T00:00:00Z (GMT) by Zhen Liu Min Shi
The asymmetric addition of cyclic β-keto esters to activated olefins and N-Boc imines was realized by using chiral cationic <i>C</i><sub>2</sub>-symmetric N-heterocyclic carbene (NHC) Pd<sup>2+</sup> diaqua complexes <b>1a</b>,<b>b</b> as the catalysts, producing the corresponding adducts in moderate to high yields (up to 95%) and with good to high enantioselectivities (up to 96% ee). Nevertheless, the most significant observation is that when the (<i>R</i>)-NHC Pd<sup>2+</sup> diaqua complex was used in these reactions, different absolute configurations were observed in comparison to those obtained with catalysts obtained from (<i>R</i>)-phosphane ligands.