Further investigations of the interaction of trimethylsilyl azide with substituted maleic anhydrides. Synthesis of 4‐ and 5‐aryl substituted 1,3‐(3H)oxazine‐2,6‐diones

The reactions of phenyl‐, o‐chlorophenyl‐, p‐chlorophenyl‐, 3,4‐dichlorophenyl‐, p‐fluoro‐ and p‐anisylmaleic anhydrides with trimethylsilyl azide are described. In all cases mixtures of isomeric 4‐ and 5‐aryl‐2H‐1,3‐(3H)oxazine‐2,6‐diones are obtained after hydrolysis with the 4‐isomer predominating. The yield of 5‐isomer is greatest for o‐chlorophenyl maleic anhydride, and substantial for other arylmaleic anhydrides, indicating increased importance of steric effects in these reactions, in contrast to previously reported syntheses of methyl and halo‐substituted oxazine‐diones, where electronic factors appeared dominant.