The enantiospecific synthesis of N2-benzyl-1-thia-2,5-diazolidin-3-one dioxides (sulfa-analogues of hydantoins) was carried out through two convergent pathways starting from chlorosulfonyl isocyanate (CSI) and chiral alpha amino- and hydroxyesters. The intermediate carboxylsulfamides (containing ''activated sulfamoyl group'') react easily in the Mitsunobu conditions to give ultimately the N-protected sulfa-hydantoins, or symmetric and dissymmetric sulfones of bis-N-aminoesters. The non-racemization during the cyclization of N-sulfamylaminoesters in alkaline conditions was established by chemical and spectroscopic methods (nmr with chiral Eu(hfc)3).
A general synthesis of 4-substituted 1,1-dioxo-1,2,5-thiadiazolidin-3-ones derived from .alpha.-amino acids