Synergic Sedation of Sensitive Anions: Alkali-Mediated Zincation of Cyclic Ethers and Ethene
Synergic Sedation of Sensitive Anions: Alkali-Mediated Zincation of Cyclic Ethers and Ethene
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DOI：
10.1126/science.1178165
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发表时间：
2009-10-30
期刊：
影响因子：
56.9
通讯作者：
Wright, Dominic S.
中科院分区：
文献类型：
--
作者：
Kennedy, Alan R.;Klett, Jan;Wright, Dominic S.
烷基和乙烯基碳-氢键的去质子化在合成中常常受到阻碍，这不仅是因为需要特别强的碱，而且还因为所得阴离子的固有不稳定性。例如，邻近氧的环醚的金属化总是引发开环分解途径。在这里，我们表明，使用一种碱可以克服这种不稳定性，通过锌-碳和钠-氧键合的合作组合。四氢呋喃和四氢吡喃两者在室温下在数天内干净地反应以产生α-锌取代的产物，其足够稳定以进行分离和晶体学表征。一个相关的锌离子的阴离子捕获策略，与钠取代钾，诱导清洁乙烯去质子化，产生一个稳定的产品。初步亲电淬灭实验与α-锌取代的环醚和苯甲酰氯得到令人满意的收率的四氢呋喃衍生的酮，但只有痕量的四氢吡喃衍生的酮。
Deprotonation of alkyl and vinyl carbon-hydrogen bonds for synthetic purposes is often hindered not merely by the need for an exceptionally strong base, but by the inherent instability of the resultant anion. Metalation of cyclic ethers adjacent to oxygen, for example, has invariably initiated a ring-opening decomposition pathway. Here, we show that the use of a bimetallic base can overcome such instability through a cooperative combination of zinc-carbon and sodium-oxygen bonding. Both tetrahydrofuran and tetrahydropyran reacted cleanly over days at room temperature to yield alpha-zinc-substituted products that were sufficiently stable to be isolated and crystallographically characterized. A related zincation-anion trapping strategy, with sodium replaced by potassium, induced clean deprotonation of ethene to yield a stable product. Preliminary electrophilic quenching experiments with the alpha-zinc-substituted cyclic ethers and benzoyl chloride gave satisfactory yields of the tetrahydrofuran-derived ketone but only trace amounts of the tetrahydropyran-derived ketone.