Phosphoric Acid Catalyzed Asymmetric 1,6-Conjugate Addition of Thioacetic Acid to para-Quinone Methides.

An asymmetric 1,6-conjugate addition of thioacetic acid with para-quinone methides has been developed by using chiral phosphoric acid catalysis in the presence of water. A series of sulfur-containing compounds were thus obtained in high yields with good to excellent enantioselectivities. Theoretical studies indicated that the water-bridged proton transfer is a potentially favorable reaction pathway. An unprecedented O-H⋅⋅⋅π interaction between water and the aromatic nucleus of chiral phosphoric acid was discovered to contribute significantly to the stereocontrol in the catalysis.