Degradation of O-arylisoureas in alkali: a low-temperature Chapman-type rearrangement

Abstract

NN′-Di-isopropyl-O-arylisoureas are demonstrated to rearrange intramolecularly to the corresponding NN′-di-isopropyl-N′-arylurea in alkaline solution. The large negative Brønsted-type β_L value (–2.3) for the reaction measured against the pK of the corresponding phenol and a modest entropy of activation are consistent with a 1,3-aryl migration. The high efficiency of the migration compared with that of the Chapman rearrangement of O-aryl imidoethers is attributed to the greater internal nucleophilicity of the imino nitrogen, which in the present case bears a negative charge.