Silver-catalyzed transformation of propargylic amine N-oxides to enones and acyloxy ketones via isoxazolinium intermediates

KGaA, Weinheim. A novel silver-catalyzed transformation of propargylic amine N-oxides with switchable product profiles has been developed. A diversity of enones with excellent E/Z ratios (up to >20:1) were obtained when the reactions were conducted in aprotic solvents. In contrast, 3-chlorobenzoxymethyl ketones and α-(3-chloro)-benzoxy enones were obtained by using protic solvents. Mechanistic studies suggested that in situ generated isoxazolinium ions are the key intermediates involved in these novel silver-catalyzed reaction pathways. Applications on the chemoselective modification of cysteine-containing peptides in aqueous medium have also been achieved.