Lee Sangjun, Hoye Thomas R
Department of Chemistry, University of Minnesota 207 Pleasant St. SE. Minneapolis Minnesota 55455 USA
Chem Sci. 2025 Jul 23. doi: 10.1039/d5sc02212f.
We describe here divergent reactivity in the intramolecular cyclizations of a family of keteniminium ions (KIs) that contain a tethered alkyne. The KI precursors were tertiary amides having (i) unsaturation (arene or alkene) located β,γ to the amide carbonyl and (ii) an alkyne tethered through the amide nitrogen atom. The KIs were generated by the action of triflic anhydride and a pyridine base at 0 °C. Substrates having a three-atom linker between the central carbon atom of the KI undergo unprecedented [4 + 2] cycloadditions between the alkyne and the styrenic/dienic subunit of the conjugated KI leading to indoline or carbazole derivatives. DFT computations suggest that the reaction proceeds by a stepwise mechanism. In contrast, substrates with a four- or five-atom tether undergo [2 + 2] cycloaddition to afford isolable, fused, cyclobutenyl iminium ions further useful as synthons.
我们在此描述了一类含有连接炔烃的烯酮亚胺离子（KI）分子内环化反应中的不同反应活性。KI前体是叔酰胺，其具有（i）位于酰胺羰基β、γ位的不饱和基团（芳烃或烯烃），以及（ii）通过酰胺氮原子连接的炔烃。KI由三氟甲磺酸酐和吡啶碱在0°C下作用生成。在KI中心碳原子之间具有三原子连接基团的底物，会在炔烃与共轭KI的苯乙烯基/二烯基亚基之间发生前所未有的[4 + 2]环加成反应，生成吲哚啉或咔唑衍生物。密度泛函理论计算表明该反应按逐步机理进行。相比之下，具有四原子或五原子连接基团的底物会发生[2 + 2]环加成反应，生成可分离的、稠合的环丁烯基亚胺离子，这些离子可进一步用作合成子。
