Synthesis of tetrahydrothiophenes
A convenient preparation of chiral tetrahydrothiophenes (THTs) in high enantiopurity via phosphorothioic acids circumvents the use of H2S which is a highly toxic gas. The key transformation is a base-promoted, intramolecular, highly stereospecific carbon-sulfur bond-forming event through a double SN2 displacement mechanism. The methodology is amenable to a broad array of functional groups and heterocycles.
F. J. Robertson, J. Wu, J. Am. Chem. Soc., 2012, 134, 2775-2780.
A bifunctional squaramide catalyzes a sulfa-Michael/aldol cascade reaction between 1,4-dithiane-2,5-diol and chalcones with a low catalyst loading to yield trisubstituted tetrahydrothiophenes with three contiguous stereogenic centers in a highly stereocontrolled manner.
J.-B. Ling, Y. Su, H.-L. Zhu, G.-Y. Wang, P.-F. Xu, Org. Lett., 2012, 14, 1090-1093.
With CuI as the catalyst and K3PO4 • 3 H2O as the base, a highly efficient, ligand-free intramolecular S-vinylation of thiols with vinyl chlorides or bromides was successfully implemented. Moreover, competition experiments revealed that the 4-exo cyclization is fundamentally preferred over other modes (5-exo, 6-exo, and 6-endo) of cyclization.
Q. Zhao, L. Li, Y. Fang, D. Sun, C. Li, J. Org. Chem., 2009, 74, 459-462.