Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, India.
Institut Universitaire de France, 1 rue Descartes, 75231, Paris, France.
Chemistry. 2020 Jan 16;26(4):818-822. doi: 10.1002/chem.201905177. Epub 2019 Dec 23.
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 α,α,α-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.
N-杂环卡宾（NHCs）在有机催化中的多样性反应性归因于其可能具有不同的作用模式。尽管已知 NHC 结合的烯醇盐和二烯醇盐，但相关的 NHC 结合的交叉共轭氮杂三烯醇盐仍然难以捉摸。在此，我们展示了 NHC 催化的含氮杂环醛与α,α,α-三氟苯乙酮的形式[6+2]环加成反应，生成多功能吡咯并恶唑酮（29 个实例）。催化生成的交叉共轭氮杂三烯醇盐（氮杂富烯型）在温和条件下与亲电酮进行了顺利的[6+2]环加成反应，以中等至良好的产率得到产物。还提供了对机理的初步 DFT 研究。
