Heterocycles from substituted amides, V. . 1,2,3,5‐Oxathiadiazolin‐4‐one 2‐oxides from thionyl chloride and N ‐hydroxyureas

The reaction of certain N ‐hydroxy‐ N ‐methyl‐ N ′‐aryl ureas, 2 , with thionyl chloride are shown to give a new heterocycle, 1,2,3,5‐oxathiadiazolin‐4‐one 2‐oxides, 3 , in a synthesis that appears to have more severe structural requirements than the previously reported ring closures from α‐hydroxyacylanilides and thionyl chloride. Isolable amounts of 3 are obtained only if the aryl group contains deactivating substituents, and the hydroxy group is attached to the N ‐alkyl nitrogen; otherwise, resin formation or ring chlorination are found to occur. The assigned structure as 3 was verified by a full three dimensional X‐ray analysis of a representative example, 3a , 3‐(4‐bromophenyl)‐5‐methyl‐1,2,3,5‐oxathiadiazolin‐4‐one.