Controllable Si−C Bond Activation Enables Stereocontrol in the Palladium‐Catalyzed [4+2] Annulation of Cyclopropenes with Benzosilacyclobutanes

• Published in: Angewandte Chemie International Edition Vol. 59; no. 2; pp. 790 - 797
• Main Authors: Wang, Xing‐Ben, Zheng, Zhan‐Jiang, Xie, Jia‐Le, Gu, Xing‐Wei, Mu, Qiu‐Chao, Yin, Guan‐Wu, Ye, Fei, Xu, Zheng, Xu, Li‐Wen
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 07.01.2020; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Activation; Chemical reactions; Chemistry; Chemistry, Multidisciplinary; Enantiomers; Heptanes; Organic chemistry; Organic compounds; Palladium; Physical Sciences; ring expansion; Science & Technology; silacycles; Si−C bond activation; Stereoselectivity; strained molecules; strained molecules; REACTIVITY; silacycles; H SILYLATION; ALKYNES; ENANTIOSELECTIVE DESYMMETRIZATION; SILICON-STEREOGENIC SILANES; ALKENES; SILACYCLOBUTANES; Si-C bond activation; ring expansion; CONSTRUCTION; CHEMISTRY; palladium; ACCESS; Si−C bond activation
• DOI: 10.1002/anie.201913060
• ISSN: 1433-7851

A novel and unusual palladium‐catalyzed [4+2] annulation of cyclopropenes with benzosilacyclobutanes is reported. This reaction occurred through chemoselective Si−C(sp2) bond activation in synergy with ring expansion/insertion of cyclopropenes to form new C(sp2)−C(sp3) and Si−C(sp3) bonds. An array of previously elusive bicyclic skeleton with high strain, silabicyclo[4.1.0]heptanes, were formed in good yields with excellent diastereoselectivity under mild conditions. An asymmetric version of the reaction with a chiral phosphoramidite ligand furnished a variety of chiral bicyclic silaheterocycle derivatives with good enantioselectivity (up to 95.5:4.5 er). Owing to the mild reaction conditions, the good stereoselectivity profile, and the ready availability of the functionalized precursors, this process constitutes a useful and straightforward strategy for the synthesis of densely functionalized silacycles. When Si−C meets C=C bond activation: Cyclopropenes were functionalized stereoselectively with benzosilacyclobutanes by palladium‐catalyzed Si−C(sp2) bond activation and a ring‐expansion/[4+2] annulation sequence to form new C(sp2)−C(sp3) and Si−C(sp3) bonds of silabicyclo[4.1.0]heptanes. The transformation provided an array of these previously elusive highly strained bicyclic skeletons in good yields with high selectivity (see scheme).