Zheng Yufen, Chen Yueyao, He Yuxuan, Rizzo Antonio, Zhou Yuchen, Low Kam-Hung, Krenske Elizabeth H, Chiu Pauline
Department of Chemistry, and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong.
Laboratory for Synthetic Chemistry and Chemical Biology Limited, Science Park, Shatin, Hong Kong.
Angew Chem Int Ed Engl. 2024 Aug 12;63(33):e202407059. doi: 10.1002/anie.202407059. Epub 2024 Jul 16.
Unexpectedly facile dearomative intramolecular (4+3) cycloadditions of thiophenes with epoxy enolsilanes, providing sulfur-bridged cycloadducts, are reported. A total of fifteen thiophene substrates have been found to undergo (4+3) cycloaddition smoothly to produce endo and exo (4+3) adducts in yields of up to 83 % with moderate to good diastereoselectivity. Complete conservation of enantiomeric purity was observed when the optically enriched epoxide was used. The desulfurizing transformations of the sulfur-bridged skeleton of the cycloadducts provide functionalized 6,7-fused bicyclic frameworks consisting of 1,3-cycloheptadiene subunits. Density functional theory calculations reveal the origins of the facile dearomatization of thiophenes in these (4+3) cycloadditions.
据报道，噻吩与环氧烯基硅烷发生了意想不到的、容易进行的分子内（4+3）环加成反应，生成了硫桥连环加成产物。总共发现有15种噻吩底物能顺利进行（4+3）环加成反应，以高达83%的产率生成内型和外型（4+3）加合物，具有中等至良好的非对映选择性。当使用光学富集的环氧化物时，对映体纯度得以完全保留。环加成产物硫桥连骨架的脱硫转化提供了由1,3-环庚二烯亚基组成的官能化6,7-稠合双环骨架。密度泛函理论计算揭示了这些（4+3）环加成反应中噻吩易于脱芳构化的原因。
