A novel method for synthesis of medium sized ring azasultams was proposed. It includes reductive cleavage with sodium cyanoborohydride of annulated 5,6-dihydro-2H-1,2,4-thiadiazine-1,1-dioxides that were prepared in bulk quantities by an improved procedure consisting of reacting cyclic imidates with taurine followed by treatment with phosphorus oxychloride in the presence of DIPEA.