Diamine-Tethered Bis(thiourea) Organocatalyst for Asymmetric Henry Reaction

We have developed a novel multifunctional C₂-symmetric biphenyl-based diamine-tethered bis(thiourea) organocatalyst, which was tested in the asymmetric Henry reaction. Under thoroughly optimized conditions, the catalyst provided exceptionally high yields and excellent enantioselectivities especially for electron-deficient aromatic and heterocyclic substrates. Due to a high affinity of the catalyst to silica gel, a simple chromatography-free nitroaldol isolation procedure was feasible. Preliminary kinetic and spectroscopic experiments were performed in order to complete the mechanistic picture of the organocatalyzed nitroaldolization process. Finally, the developed synthetic strategy was successfully applied to the catalytic enantioselective syntheses of enantiopure (S)-econazole and (R)-mirabegron a late-stage intermediate.