Metal-Free Photoinduced Cascade Cyclization of Alkyne-Tethered N -Alkoxybenzamides

In this work, a photoinduced synthesis of isoxazolidinefused isoquinolin-1-ones and 3,4-dihydro[1,2]oxazino[2,3-b]isoquino- lin-10(2H)-one from alkyne-tethered N-alkoxybenzamides is reported. The gram-scaled synthesis and structural elaboration of isoxazolidinefused isoquinolin-1-ones are also realized. The reaction is promoted by an equimolar amount of tetrabutylammonium chloride, under metal- and catalyst-free conditions. In the reaction, it is believed that the alkyne-tethered N-alkoxybenzamide starting materials serve as photo- sensitizers, and the photoexcited substrate induces the formation of a chloro radical. The N-radical results from hydrogen atom abstraction by the chloro radical at the N-H bond of the substrates.