Phenolate‐Induced N−O Bond Formation versus TiemannType Rearrangement for the Synthesis of 3‐Aminobenzisoxazoles and 2‐Aminobenzoxazoles

A novel oxadiazolone‐based method for the synthesis of 3‐aminobenzisoxazoles by N−O bond formation and of 2‐aminobenzoxazoles through a Tiemann‐type rearrangement has been developed. The synthesis of these two pharmaceutically relevant heterocycles was realized by an unexplored retrosynthetic disconnection using a cyclic nitrenoid precursor‐based strategy. The selective formation of the two isomers was significantly influenced by steric and electronic effects of substituents. However, tetrabutylammonium chloride (TBACl) efficiently promoted the Tiemann‐type rearrangement over N−O bond formation. Control experiments indicate that deprotonation of the phenol induces both rearrangements.