Chemoselective Amination of beta-Keto Amides

摘要

Both carbonyl groups of a beta-keto amide are highly activated by intramolecular hydrogen bonding. Hence, beta-keto amides readily undergo amination, giving either beta-aminobutenamides or N-substituted acetoacetamides. The chemoselectivity was influenced by the steric bulk of the keto amide or the amine: while amination at the ketone moiety pre-dominated at low temperatures with less hindered substrates, amination at the amide moiety occurred at higher temperatures with sterically hindered substrates. In addition, a beta-aminobutenamide with a bulky amino group was converted to an N-substituted acetoacetamide by simply heating to a high temperature. Based on the experimental results, as well as density functional theory (DFT) calculations, N-substituted acetoacetamides were more stable than beta-aminobutenamides when the amino group is bulky. This reaction allows the direct synthesis of N-substituted acetoacetamides from N-unsubstituted acetoacetamides.