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郑州大学吴养洁院士、崔秀灵教授课题组发展了一种铜催化肟酯、烯醇硅醚和单质硫的三组分串联环化反应，烯醇硅醚作为C1合成子参与了环化反应，生成一系列2-芳酰基萘并噻唑和2-芳酰基苯并噻吩并噻唑。所得产物显示出良好的荧光性质，在功能材料方面具有潜在应用价值。
烯醇硅醚作为一类至关重要的合成中间体，广泛地应用于C-C键的构建。尤其是，烯醇硅醚的环化反应近期引起了化学家的关注，这主要归因于其作为C2合成子能够高效合成多种多元环及杂环结构，值得注意的是，关于烯醇硅醚作为C1合成子在环化反应中的潜力与应用，目前尚缺乏充分而深入的研究。同时，作者发现单质硫（S8）与适宜的碱反应能够较为容易地生成三硫自由基阴离子，由此提出了一个设想：肟酯有可能通过与三硫自由基阴离子发生亲核取代反应，进而生成亚氨基硫自由基。这一亚氨基硫自由基随后会经历一个1,3-H迁移过程，从而衍生出硫中心自由基中间体。该中间体有望与烯醇硅醚发生自由基加成反应，随后通过分子内环化得到最终产物。这一研究设想为烯醇硅醚在环化反应中的应用提供了新的思路。 在建立优化反应条件后，作者对底物范围进行了考察（图2）。结果显示，该反应对各种官能团具有良好的兼容性。此外，作者通过对底物结构的改变，将1-四氢萘酮肟酯替换为可作为C4合成子的苯乙酮肟酯，实现了单质硫在该反应中提供了两个硫原子从而在铜催化下构建了两个含硫杂环合成了一系列2-芳酰基噻吩并噻唑类化合物（图3）。 图2 1-四氢萘酮肟和烯醇硅醚的底物拓展 图3 苯乙酮肟的底物拓展 为了探究该反应的机理，作者设计了多个控制实验（图4）。首先，在标准条件下，当用苯乙酮代替烯醇硅醚（2a）作为起始原料时，不能得到目标产物3aa。这一结果证明了三甲基硅烷基（TMS）可能在该转化中起着至关重要的作用，一定程度上提高了反应的活性和选择性。此外，自由基抑制实验结果表明该反应可能是自由基路径。进一步的EPR研究表明，三硫自由基阴离子是该反应的关键中间体。 图4 控制实验以及EPR研究 综上，该课题组开发了一种新颖的合成策略，用于制备2-取代萘并噻唑及噻吩并噻唑类化合物。在此策略中，烯醇硅醚作为C1合成子参与环化反应。该合成方法不仅底物适用范围广泛，官能团耐受性优良，且易于实现规模化生产。 论文信息 Cu-Catalyzed [3+1+1] Cascade Cyclization of O-Acyl Oximes with Sulfur and Silyl Enol Ethers: Rapid Access to Naphthothiazoles Xiaofan Cui, Shi Sheng, Chao Pi, Yangjie Wu, Xiuling Cui Chemistry – A European Journal DOI: 10.1002/chem.202402976
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