Screening of a modular sugar-based phosphite ligand library in the asymmetric nickel-catalyzed trialkylaluminum addition to aldehydes

We synthesized a modular sugar-based phosphite ligand library for the Ni-catalyzed trialkylaluminum addition to aldehydes. This library has been designed to rapidly screen the ligands to uncover their important structure features and determine the scope of the phosphite ligands in this catalytic reaction. After systematic variation of the sugar backbone, the substituents at the phosphite moieties, and the flexibility of the ligand backbone, the monophosphite ligand 1,2:5,6-di-O-isopropylidene-3-O-((3,3';5,5'-tetra-tert-butyl-1,1'-biphenyl-2,2'-diyl)phosphite)-alpha-D-glucofuranose 1c was found to be optimal, yielding high activities and enantioselectivities (ee's up to 94%) for several aryl aldehydes.