Cyclocarbonickelation–Arylation Cascade under Ligand-Free Conditions: Access to Dibenzoxepine, Oxathiepine, and Thiazepine Frameworks and Mechanistic Insights

A ligand-free, nickel-catalyzed one-pot cyclocarbonickelation-arylation cascade of functionalized bromoalkyne substrates enables efficient and regioselective access to dibenzoxepine, dibenzoxathiepine, and dibenzothiazepine frameworks in good to high yields. This method exhibits a broad functional group tolerance, including electron-rich, electron-poor, heteroaryl, and terminal alkynes and is also effective under microwave irradiation. Detailed DFT studies support a Ni(I)/Ni(III) pathway involving oxidative addition, migratory insertion, and reductive elimination, consistent with the observed regio- and stereoselectivity.