Kinetic and thermodynamic control in the cyclization via thiiranium ions. Stereoselective synthesis of a 2,3,5trisubstituted tetrahydropyran ring

The stereoselective rearrangement of tetrahydrofuran or tetrahydropyran rings having a phenylsulfanyl group in an exoposition, viathe intermediate thiiranium ions, is reported. The 5 or 6exotet cyclization of hydroxy sulfides gave the kinetic products while the 6endotet or 5endotet gave the thermodynamic products. The rearrangement of the 5exoproduct to the 6endo one is an interesting way for the stereoselective synthesis of substituted tetrahydropyrans.