基与六甲基基化的反应:竞争性化和1,2-添加
Pinjing Zhao1, Anthony Condo, Ivan Keresztes
1Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Journal of the American Chemical Society
|March 12, 2004
概括
溶剂会影响2 - 甲基环松与六甲基二甲基化物 (LiHMDS) 的反应. 根据溶剂,LiHMDS可以促进乙醇化或1,2-添加反应.
科学领域:
- 有机化学 有机化学
- 反应机制 反应机制
- 频谱学是一种光谱学.
背景情况:
- 六甲基西拉化物 (LiHMDS) 是一种强大的非核基,通常用于有机合成.
- 涉及LiHMDS的反应的化学选择性可能会受到溶剂选择和反应条件的影响.
- 了解这些影响对于控制合成结果至关重要.
研究的目的:
- 为了研究与LiHMDS.的2-甲基环松反应的依赖溶剂的化学选择性.
- 阐明这些转化所涉及的反应途径和中间体.
- 为了确定不同反应结果之间的分区的动力控制.
主要方法:
- 现场红外 (IR) 光谱用于速率研究.
- 核磁共振 (NMR) 光谱学 ((6) Li, (15) N 和 (13) C) 用于结构阐明.
- 动力学研究来分析反应途径.
主要成果:
- 在THF/托卢中,LiHMDS促进化,反应速率取决于THF度,并通过基于单体的途径进行.
- 在pyrrolidine/toluene中,LiHMDS仅产生1,2-添加,形成一个alpha-amino alkoxide-LiHMDS混合二元体.
- 双重体存在于一对对应体中,其特点是先进的NMR技术.
- 动力学研究表明1,2-加法通路的基于单体的过渡结构.
结论:
- 反应结果 (乙烯化与1,2-添加) 由溶剂系统决定.
- 反应途径依赖于度,在两个观察到的情况下都通过单体物种进行.
- 观察到的化学选择性在动力控制下,突出显示了反应条件在指导合成结果中的重要性.
相关概念视频
Nucleophilic Addition to the Carbonyl Group: General Mechanism
The carbonyl carbon in an aldehyde or ketone is the site of a nucleophilic attack due to its electron-deficient nature. Depending on the strength of the incoming nucleophile, the reaction occurs via different mechanistic pathways.
A stronger nucleophile can directly attack the electrophilic center, the carbonyl carbon. The HOMO orbital of the nucleophile interacts with the LUMO (π* antibonding) orbital present on the carbonyl carbon. This interaction breaks the π bond and shifts the π bonding...
A stronger nucleophile can directly attack the electrophilic center, the carbonyl carbon. The HOMO orbital of the nucleophile interacts with the LUMO (π* antibonding) orbital present on the carbonyl carbon. This interaction breaks the π bond and shifts the π bonding...
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