Copper-catalyzed alkyne oxidation/Buchner-type ring-expansion to access benzo[6,7]azepino[2,3-b]quinolines and pyridine-based diones

作者：Jiang, Xiao-Lei; Liu, Qing; Wei, Kua-Fei; Zhang, Ting-Ting; Ma, Guang; Zhu, Xiu-Hong; Ru, Guang-Xin^*; Liu, Lijie^*; Hu, Lian-Rui^*; Shen, Wen-Bo^*

来源：Communications Chemistry, 2023, 6(1): 35.

DOI：10.1038/s42004-023-00840-6

• OXO GOLD CARBENES
• C-C
• NEGATIVE SOLVATOCHROMISM
• OXIDATIVE CYCLIZATIONS
• METAL-FREE
• N-OXIDES
• OXIDATION/CYCLOPROPANATION
• DEAROMATIZATION
• GENERATION
• DIVERGENT

Organic molecules containing seven-membered rings are important structural motifs for drug candidates, but the construction of seven-membered rings can be challenging through traditional cyclization pathways. Here, the authors report a copper-catalyzed alkyne oxidation and Buchner-type ring-expansion to generate benzo[6,7]azepino[2,3-b]quinolines and pyridine-based diones. @@@ General access to highly valuable seven-membered rings via Buchner-type reaction remains a formidable challenge. Here we report a Cu-catalyzed intermolecular oxidation of alkynes using N-oxides as oxidants, which enables expedient preparation of valuable benzo[6,7]azepino[2,3-b]quinolines and pyridine-based diones. Importantly, in contrast to the well-established gold-catalyzed intermolecular alkyne oxidation, the dissociated pyridine or quinoline partner could be further utilized to construct N-heterocycles in this system and the reaction most likely proceeds by a Buchner-type ring expansion pathway. A mechanistic rationale for this cascade cyclization is supported by DFT calculations.