从终端基合成高替代基
Bradley W Gardner1, Crystal P Chung1, Michael R Pu1
1Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
这项研究引入了一种用于制造复杂三基和四基替代的新催化方法. 这种方法精确地控制了替代剂的配置,克服了有机合成的重大挑战.
科学领域:
- 有机化学
- 合成化学
背景情况:
- 在生物活性分子和合成过程中至关重要.
- 已经确定了单基和异基的有效合成.
- 选择性合成三基和四基替代仍然是一个挑战.
研究的目的:
- 开发一种用于合成三基和四基替代的新方法.
- 为了能够精确地控制同位素的产生.
主要方法:
- 终端基与基和有机基的催化合.
- 使用独特的反应机制来定位替代剂.
- 使用与终端基和质子源的基,以获得补充性的立体选择性.
主要成果:
- 成功合成三基和四基替代.
- 精确控制替代物的相对位置.
- 在三替代合成中证明了补充性的立体选择性.
结论:
- 这种新型的催化合提供了一种高效和精确的途径,使多种类型的同位素.
- 这种方法解决了有机化学中的重要合成挑战.
- 扩大对各种应用的高度替代的使用范围.
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相关概念视频
02:27Preparation of Alkynes: Alkylation Reaction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:34Preparation of Alkynes: Dehydrohalogenation
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
02:42Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
01:33Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.