Phosphorothioic Acids and Related Compounds as Surrogates for H₂SSynthesis of Chiral Tetrahydrothiophenes

The convenient preparation of chiral tetrahydrothiophenes (THTs) in high enantiopurity via phosphorothioic acids and related compounds is reported. We consider these to be safer alternatives to the use of H₂S which is a highly toxic gas. Each of the THTs is derived from a common intermediate, thereby greatly enhancing the flexibility of the synthesis. The key transformation is a base-promoted, intramolecular, carbon–sulfur bond-forming event. These reactions are highly stereospecific as they operate through a double S_N2 displacement mechanism. The methodology is amenable to a broad array of functional groups and heterocycles. The tetrahydrothiophene motif is important because it is present in a number of bioactive natural products. They have also been utilized to promote various asymmetric transformations including hydrogenation, epoxidation, cyclopropanation, and aziridination reactions.