Synthesis of dihydro-1,4-thiazine from α-keto spiro-thiazolidine

Abstract

The reaction of α-bromocycloalkanone with 2-aminoethanthiol leads to the regioselective formation of spirothiazolidin-2-one with the oxo-group migrating to the original position occupied by the halogen atom. The reaction of 1-thia-4-azaspiro[4.5]alkan-6-one with bromine, iodine, copper (II) salts, acid or base gives dihydro-1,4-thiazine derivatives in moderate yields. Moreover, the treatment of the spiro-thiazolidine derivatives on silica gel under microwave gives the 1,4-thiazine compound.