General and Chemoselective N-Transacylation of Secondary Amides by Means of Perfluorinated Anhydrides

摘要

Examples of direct N-transacylations of amides are very rare and lacking in general applicability. For instance, earlier attempts at N-transacylation were performed under harsh conditions. Other procedures required prolonged treatment with an equimolar mixture of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA; 100°C, 48 h), or even running the reaction in TFAA followed by the addition of a strong base, reported as necessary to abstract the hydrogen atom in the alpha position to the eliminated acyl group. Finally, some acetanilides were treated with chloroacetyl chloride under acid catalysis of zeolites or AlCl3 at 83°C for 16 h, or in refluxing pyridine containing dimethylaminopyr-idine for 5 h.