Darbeau RW, White EH, Nunez N, Coit B, Daigle M
Departments of Chemistry, McNeese State University, Lake Charles, Louisiana 70609 and The Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Org Chem. 2000 Feb 25;65(4):1115-20. doi: 10.1021/jo991600n.
Benzyl cations were generated via the thermal decomposition of N-benzyl-N-nitrosopivalamide in acetonitrile and acetonitrile-water mixtures at 25 degrees C. The first-formed (primary) benzylating agent, the benzyl cation, was scavenged competitively by pivalate (trimethyl acetate) ion to yield benzyl pivalate, by acetonitrile to yield the corresponding N-benzylnitrilium ion, and by water (when present) to yield benzyl alcohol. The nitrilium ion underwent a cascade of reactions to yield an array of products whose identities and relative yields as a function of time were used to elucidate the mechanistic paths involved. Thus, the N-benzylnitrilium ion reacted with pivalate ion to yield the Z-isomer of N-benzylethanimidic pivalic anhydride, followed by its conversion into the E-isomer. This article appears to be the first to document compounds of this type. The E-isomer is labile under the reaction conditions, rearranging into N-acetyl-N-pivalylbenzylamine. In the presence of water as a diluent, a significant fraction of the nitrosoamide was hydrolyzed to benzyl alcohol; hydrolysis of the nitrilium ion yielded N-benzyl acetamide. The yield of hydrosylates was directly proportional to the mole fraction of water in the medium.
苄基阳离子通过N-苄基-N-亚硝基新戊酰胺在25℃的乙腈和乙腈-水混合物中的热分解产生。首先形成的（初级）苄基化剂，即苄基阳离子，会被新戊酸根（三甲基乙酸根）离子竞争性清除，生成苄基新戊酸酯；被乙腈清除，生成相应的N-苄基腈鎓离子；被水（如果存在）清除，生成苄醇。腈鎓离子经历一系列反应，生成一系列产物，这些产物的身份和相对产率随时间变化，用于阐明其中涉及的反应机理路径。因此，N-苄基腈鎓离子与新戊酸根离子反应，生成N-苄基乙亚胺新戊酸酐的Z-异构体，随后转化为E-异构体。本文似乎是首次记录此类化合物。E-异构体在反应条件下不稳定，重排为N-乙酰基-N-新戊酰基苄胺。在水作为稀释剂存在的情况下，相当一部分亚硝基酰胺水解为苄醇；腈鎓离子水解生成N-苄基乙酰胺。水解产物的产率与介质中水的摩尔分数成正比。
