Palladium-Catalyzed Intramolecular Cyclization of Ynamides: Synthesis of 4‑Halo-oxazolones

A mild
and efficient methodology involving Pd­(PPh3)4-catalyzed intramolecular cyclization of N-alkynyl
alkyloxycarbamates with CuCl2 or CuBr2 for the
synthesis of 4-halo-oxazolones was developed. This reaction
exhibiting good functional tolerance provided a new, efficient, and
rapid synthetic process to 4-halo-oxazolones. The resulting 4-halo-oxazolones
can serve as great potential precursors for the 3,4,5-trisubstituted
oxazolones via a Pd-catalyzed cross-coupling reaction.