N-Heterocyclic Carbene-Catalyzed Formal [6+2] Annulation Reaction via Cross-Conjugated Aza-Trienolate Intermediates
N-Heterocyclic Carbene-Catalyzed Formal [6+2] Annulation Reaction via Cross-Conjugated Aza-Trienolate Intermediates
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DOI：
10.1002/chem.201905177
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发表时间：
2019-12-23
影响因子：
4.3
通讯作者：
Biju, Akkattu T.
中科院分区：
文献类型：
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作者：
Balanna, Kuruva;Madica, Krishnaprasad;Biju, Akkattu T.
N-杂环卡宾在有机催化反应中的多样性是由于其可能具有不同的作用模式。尽管NHC结合的烯醇化物和二烯醇化物是已知的，但相关的NHC结合的交叉缀合的氮杂三烯醇化物仍然是难以捉摸的。在此，我们证明了NHC催化的含氮杂环醛与α，α，α-三氟苯乙酮的形式[6+2]环化，导致形成多功能的吡咯并恶唑酮（29个实施例）。催化生成的交叉共轭的氮杂-三烯醇酯（氮杂-富烯型）与亲电酮进行平滑的[6+2]成环，以在温和条件下以中等至良好的产率得到产物。初步DFT研究的机制也提供。
The diverse reactivity of N-heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modes of action. Although NHC-bound enolates and dienolates are known, the related NHC-bound cross-conjugated aza-trienolates remain elusive. Herein, we demonstrate the NHC-catalyzed formal [6+2] annulation of nitrogen-containing heterocyclic aldehydes with alpha,alpha,alpha-trifluoroacetophenones leading to the formation of versatile pyrrolooxazolones (29 examples). The catalytically generated cross-conjugated aza-trienolates (aza-fulvene type) underwent smooth [6+2] annulation with electrophilic ketones to afford the product in moderate to good yields under mild conditions. Preliminary DFT studies on the mechanism are also provided.