α,β-Unsaturated acyl azoliums from N-heterocyclic carbene catalyzed reactions: observation and mechanistic investigation.
α,β-Unsaturated acyl azoliums from N-heterocyclic carbene catalyzed reactions: observation and mechanistic investigation.
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DOI：
10.1002/anie.201005352
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发表时间：
2011-02-11
影响因子：
16.6
通讯作者：
Bode, Jeffrey W.
中科院分区：
文献类型：
--
作者：
Mahatthananchai, Jessada;Zheng, Pinguan;Bode, Jeffrey W.
催化生成的酰基唑鎓 I 及其 α,β-不饱和对应物 II 被认为是 N-杂环卡宾 (NHC) 催化剂促进的快速增长的转化中的关键反应中间体。自 2004 年以来报道的几乎所有新的 NHC 催化的 α-官能化醛反应的假定催化循环中都引用了酰基唑鎓，其中通常认为它们具有活化羧酸的反应性，即类似于活化酯。在 NHC 催化过程中，它们通常是通过官能化醛的内部氧化还原反应获得的，但也可以通过 Breslow 中间体的氧化或乙烯酮的加成来制备。酰基唑鎓 I 是焦磷酸硫胺素 (ThPP) 依赖性酶反应的重要中间体。汤森等人。最近提出不饱和酰基唑鎓III是克拉维酸生物合成的关键中间体；尽管付出了精心的努力，III或其类似物II从未被表征或独立合成。在这里，我们记录了 α,β-不饱和酰基唑鎓 1 和 2（方案 1）的观察和表征，并证明它们相应的半缩醛（1' 和 2”）是其酰化和环化反应中动力学上重要的中间体。
Catalytically generated acyl azoliums I and their α,β-unsaturated counterparts II are thought to be key reactive intermediates in a rapidly growing number of transformations promoted by N-heterocyclic carbene (NHC) catalysts. Acyl azoliums are invoked in the postulated catalytic cycles of nearly all of the new NHC-catalyzed reactions of α-functionalized aldehydes reported since 2004, in which they are generally assumed to possess the reactivity of an activated carboxylic acid, that is, analogous to an activated ester. In NHC-catalyzed processes, they are most often obtained through internal redox reactions of functionalized aldehydes but have also been prepared by oxidations of the Breslow intermediates or additions to ketenes. Acyl azoliums I are important intermediates in thiamine pyrophosphate (ThPP) dependent enzymatic reactions. Townsend et al. have recently proposed that unsaturated acyl azolium III is the key intermediate in clavulanic acid biosynthesis; despite careful efforts, III or its analogues II have never been characterized or independently synthesized. Here, we document the observation and characterization of α,β-unsaturated acyl azoliums 1 and 2 (Scheme 1) and demonstrate that their corresponding hemiacetals (1′ and 2”) are the kinetically important intermediates in both their acylation and annulation reactions.
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影响因子：
1.8
作者：
BRESLOW, R;KIM, R
通讯作者：
KIM, R
影响因子：
16.6
作者：
De Sarkar, Suman;Studer, Armido
通讯作者：
Studer, Armido
影响因子：
16.6
作者：
Guin, Joyram;De Sarkar, Suman;Studer, Armido
通讯作者：
Studer, Armido
影响因子：
16.6
作者：
Burstein, C;Glorius, F
通讯作者：
Glorius, F
影响因子：
5.2
作者：
Candish, Lisa;Lupton, David W.
通讯作者：
Lupton, David W.