Iridium(III)-Catalyzed Direct Intermolecular Chemoselective α‑Amidation of Masked Aliphatic Carboxylic Acids with Dioxazolones via Nitrene Transfer

The Ir­(III)-catalyzed direct α-C–H
amidation of imidazole-masked
aliphatic carboxylic acids with dioxazolones is reported. The presence
of an imidazole moiety as a directing group is a key to the success
of the reaction. The products can be easily converted to esters and
amides in a simple procedure. The reaction shows a broad substrate
scope for various substituted 2-acylimidazoles, as well as a variety
of dioxazolone derivatives with important functional groups being
tolerated. The reaction mechanism was investigated by deuterium-labeling
experiments, Hammett plots, NMR, and FAB-MS, and we propose the generation
of an iridium nitrene intermediate.