New axially chiral bis(dihydrooxazoles) as ligands in stereoselective transition-metal catalysis

The new, axially chiral bis(4,5-dihydrooxazoles) 4 have been synthesized in a straightforward manner, starting from the substituted, racemic 1,1'-biphenyl-2,2'-dicarboxylic acids 1 and optically active amino alcohols 2. The adducts were resolved by medium-performance liquid chromatography (MPLC : see Scheme 1). Formation of Cn(I) complexes of 4 was followed by H-1-NMR spectroscopy. The catalytic behavior of these complexes has been investigated by asymmetric cyclopropanation of styrene with ethyl diazoacetate. Beside the influence of steric factors, a significant electronic effect on asymmetric induction could also be observed (see Scheme 2 and Table).