Abstract

Background: The versatile 2-alkynylbenzamde has been reported to produce many privileged skeletons, like isoquinolin-1-ones, isocoumarin-1-imines, isoindolin-1-ones, and isobenzofuran- 1-imines. Recently, we reported the projected transformation using copper salt (CuCl2) as a catalyst under the O₂ atmosphere. To expand the scope of the reaction, we used another inexpensive metal salt, MnO₂, as a catalyst.

Methods: The paper aims to explore a manganese-catalyzed reaction of 2-alkynylbenzamide under an O₂ balloon for the synthesis of 3-hydroxylisoquinolin-1,4-dione.

Results: Results on reaction scope shows the 10 mol% MnO₂ in O₂ atmosphere and DCE solvent catalyzed the cyclization of 2-alkynylbenzamide to produce 3-hydroxylisoquinolin-1,4-diones in 40-68% isolated yields. The reaction proceeds through a regioselective N-center radical 6-endo-dig aza-cyclization pathway.

Conclusion: We have developed a manganese-catalyzed cyclization of 2-alkynlbenzamide for the synthesis of 3-hydroxylisoquinolin-1,4-diones under an O₂ balloon. It is believed that the N-center radical-based 6-endo dig aza-cyclization proceeded in a regioselective manner.

Keywords: 2-Alkynylbenzamide, manganese catalysis, hydroxyliosoquinolin-1, 4-dione, 6-endo-dig cyclization, catalyst, MnO₂.