Screening of modular sugar phosphite-oxazoline and phosphite-phosphoroamidite ligand libraries in the asymmetric nickel-catalyzed trialkylaluminium addition to aldehydes

Modular sugar phosphite-oxazoline L1–L5a–c and phosphite-phosphoroamidite L6a–c ligand libraries were screened in the asymmetric Ni-catalyzed 1,2-addition reactions to aldehydes. Systematically varying the electronic and steric properties of the oxazoline and biaryl phosphite substituents and the functional groups attached to the basic sugar-backbone, we found a strong influence of the oxazoline and the functional groups of the sugar-backbone on the catalytic performance. Enantioselectivity (ee values up to 59%) was best with the catalysts precursor containing the phosphite-oxazoline ligand L3a, that contains a sterically hindered tert-butyl oxazoline group.