Resolution of Vaulted Biaryl Ligands via Borate Esters of Quinine and Quinidine.

Given the sudden and unexplained rise in the cost of (+)- and (-)-sparteine, an alternative method for the resolution of vaulted biaryls has been developed. This method involves the reaction of a racemic vaulted biaryl ligand with one equivalent of BH·SMe and one equivalent of either quinine or quinidine. A precipitate then forms from the resulting mixture of diastereomeric borates as a result of differential solubilities.