Boryl Radical as a Catalyst in Enabling Intra‐ and Intermolecular Cascade Radical Cyclization Reactions: Construction of Polycyclic Molecules

• Published in: Angewandte Chemie International Edition 2024-06, Vol.63 (25), p.e202405863-n/a
• Main Authors: Wang, Jie, Lin Phang, Yee, Yu, You‐Jie, Liu, Nan‐Nan, Xie, Qiang, Zhang, Feng‐Lian, Jin, Ji‐Kang, Wang, Yi‐Feng
• Format: Article
• Language: English
• Subjects: Alkynes; Assembling; boryl radical; Cascade chemical reactions; Catalysts; Chemical reactions; Cycloaddition; polycyclic molecules; radical cascade reactions; radical catalysis; Radicals; Stereoselectivity; Substrates
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202405863

Cascade radical cyclization constitutes an atom‐ and step‐economic route for rapid assembly of polycyclic molecular skeletons. Although an array of redox‐active metal catalysts has recently shown robust applications in enabling various catalytic cascade radical processes, the use of free organic radical as the catalyst, which is capable of triggering strategically distinct cascades, has rarely been developed. Here, we disclosed that the benzimidazolium‐based N‐heterocyclic carbene (NHC)‐boryl radical is capable of catalyzing cascade cyclization reactions in both intra‐ and intermolecular pathways, assembling [5,5] fused bicyclic and [6,6,6] fused tricyclic molecules, respectively. The catalytic reactions start with the chemo‐ and regioselective addition of the boryl radical catalyst to a tethered alkene or alkyne moiety, followed by either an intramolecular formal [3+2] or an intermolecular [2+2+2] cycloaddition process to construct bicyclo[3.3.0]octane or tetrahydrophenanthridine skeletons, respectively. Eventually, a β‐elimination occurs to release the boryl radical catalyst, completing a catalytic cycle. High to excellent diastereoselectivity is achieved in both catalytic reactions under substrate control. Benzimidazolium‐based N‐heterocyclic carbene (NHC)‐boryl radical catalyzes cascade cyclization reactions to construct polycyclic compounds both intra‐ and intermolecularly. This catalytic cascade radical reaction allows rapid construction of complex molecular architectures through the formation of two or three bonds in a single operation, respectively.