O-Alkyl-N-acyl-N-phenylhydroxylamines as Photochemical Alkoxy Radical Precursors

Abstract

A simple and efficient technique for the photolysis of alkoxy radical precursors is developed. Irradiation of <i>O</i>-alkyl-<i>N</i>-acyl-<i>N</i>-phenylhydroxylamines, as representative alkoxy radical precursors, with ultraviolet light (≥254 nm) results in homolytic N–O bond cleavage to generate singlet alkoxy and acylaminyl caged radical pairs. These radicals, depending on the solvent employed, either escape from the cage to form fragmentation products, or undergo in-cage reactions to produce photorearrangement products. The homolytic cleavage of the N–O bond is analyzed using time-dependent­ density functional theory calculations. The nature of the <i>N</i>-acyl substituent on the <i>O</i>-alkyl-<i>N</i>-acyl-<i>N</i>-phenylhydroxylamines is shown to influence their ability to generate radicals. Furthermore, identification and trapping of the alkoxy radicals is demonstrated.