Halolactonization of Alkenoic Acid Catalyzed by Ammonium Iodide

Abstract

A novel halolactonization of pentenoic acids was developed,which was catalyzed by hypervalent iodine species generated in situ from ammonium iodide. In this protocol,4-pentenoic acids reacted easily with lithium bromide or lithium chloride under catalyst ammonium iodide in combination with m-chloroperbenzoic acid( mCPBA) as the terminal oxidant in CH 3 CN at room temperature,which provided five-membered halolactones in moderate to good yields. A new plausible reaction pathway for the reaction was hypothesized. Thus, NH 4 I was first oxidized to I 2 and HOI with mCPBA,both of them reacted with alkenoic acid to form the iodolactone,which then was transformed into the hypervalent iodine intermediate in situ by the continuing oxidation, and finally the halolactone was provided when lithium bromide or lithium chloride was acted as nucleophile in the following intermolecular nucleophilic substitution. This method has some advantages such as mild reaction conditions,simple procedure and good yields. Furthermore,the scope of hypervalent iodine reagents in organic synthesis could be extended.