Catalytic Enantioselective Addition of Cyclic β-Keto Esters with Activated Olefins and N-Boc Imines Using Chiral C2-Symmetric Cationic Pd2+ 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 C2-symmetric N-heterocyclic carbene (NHC) Pd2+ diaqua complexes 1a,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 (R)-NHC Pd2+ diaqua complex was used in these reactions, different absolute configurations were observed in comparison to those obtained with catalysts obtained from (R)-phosphane ligands.