Competitive Base-Induced α-Elimination and Methanolysis of N-Aryl-O-pivaloylhydroxylamines

Article abstract of DOI:10.1021/jo00297a015

The N-aryl-O-pivaloylhydroxylamines 1a-c are quite stable in MeOH under neutral conditions, but under mildly basic conditions (0.05 M Et2NH or Et3N) they undergo rapid decomposition (t_1/2 = ca. 3-5 h at 25 deg C) by two competitive processes: apparent α-elimination to generate the nitrenes 2a-c and pivalic acid and basic ester methanolysis to generate the hydroxylamines 3a-c and methyl pivalate.The nitrenes decompose into the corresponding anilines 5 and azobenzenes 7, while the hydroxylamines undergo nitrene-mediated oxidation into the corresponding azoxybenzenes 6.The mechanism of this latter process was probed by addition of excess hydroxylamine, and a mechanism for the oxidation consistent with available data (Scheme II) is proposed.It was also found that the nitrosobenzenes 8 undergo nucleophilic attack by conjugate bases 4a-c of the title compounds to produce one of the two possible isomeric nonsymmetrical azoxybenzenes.