Resolution of the atropochiral biminap ligand and applications in asymmetric catalysis.
Enantiomeric resolution of the rac-biminap ligand is achieved through fractional crystallization of four diastereoisomeric palladium complexes involving ortho-metallated enantiomerically pure (R)-dimethyl(1-naphthylethyl)amine as a chiral auxiliary. After decomplexation, the absolute configuration of (R)-biminap and (S)-biminap has been unambiguously attributed by single-crystal X-ray crystallography, and their stereochemical purity is confirmed by measurement of their optical rotation and by re-derivatization with the initial resolving chiral complex. Palladium complexes of biminap are shown to efficiently catalyze Tsuji-Trost allylic substitution of 3-acetoxy-1,3-diphenylpropene by sodium dimethyl malonate. In the asymmetric version using the enantiomerically pure (R)-biminap ligand, significant solvent and anion effects are evident, and an ee up to 90% is obtained.