烯酸在碘化铵催化作用下的卤代内酯化反应

Halolactonization of Alkenoic Acid Catalyzed by Ammonium Iodide

研究了不饱和烯酸在碘化铵催化作用下的溴代和氯代内酯化反应.通过该反应,4-戊烯酸等不饱和烯酸在催化剂碘化铵和氧化剂间氯过氧苯甲酸作用下很容易与溴化锂和氯化锂反应,常温下短时间内即可得到良好产率的溴/氯甲基γ-丁内酯化合物,从而建立了一个简单快速合成溴/氯甲基γ-丁内酯的新方法.考察了反应条件对反应的影响,提出了该反应是经过有机高价碘中间体而进行的反应机理.

A novel halolactonization of pentenoic acids was developed, which was catalyzed by hypervalent io-dine 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 CH3 CN at room temperature, which provided five-membered halolac-tones in moderate to good yields. A new plausible reaction pathway for the reaction was hypothesized. Thus, NH4 I was first oxidized to I2 and HOI with mCPBA, both of them reacted with alkenoic acid to form the iodola-ctone, 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.