Thia-Prins Bicyclization Approach for the Stereoselective Synthesis of Dithia- and Azathia-Bicycles

A novel thia-Prins bicyclization approach has been developed for the first time for the synthesis of hexahydro-2H-thieno­[3,2-c]­thiopyran derivatives from the coupling of homoallylic mercaptans such as hex-3-ene-1,6-dithiol with various aldehydes using 10 mol % InBr3 in dichloromethane with high selectivity. In addition, the coupling of (E)-N-(6-mercaptohex-3-enyl)-4-methylbenzenesulfonamide with aldedydes affords the corresponding N-tosyloctahydrothiopyrano­[4,3-b]­pyrrole derivatives in good yields. This reaction is a stereoselective affording trans-fused product from E-homoallyllic mercaptan and cis-fused product from Z-homoallyllic mercaptan.