Highly Effective Configurational Assignment Using Bisthioureas as Chiral Solvating Agents in the Presence of DABCO

A highly effective (1)H NMR method for determining the absolute configurations of various chiral α-hydroxyl acids and their derivatives has been developed with the use of bisthioureas (R)-CSA 1 and (S)-CSA 1 as chiral solvating agents in the presence of DABCO, giving distinguishable proton signals with up to 0.66 ppm chemical shift nonequivalence. Computational modeling studies were performed with Gaussian09 to reveal the chiral recognition mechanism.