Synthesis of <i>cis</i>-fused-oxazolo/oxazino-isoquinolinones <i>via</i> photocascade reaction

A method for the selective synthesis of <i>cis</i>-fused-oxazoloisoquinolinones (2-α, 2-β) and <i>cis</i>-fused-oxazinoisoquinolinones (4-α, 4-β) <i>via</i> the visible light photo cascade reaction of (<i>E</i>)-1-(2-hydroxyethyl/propyl)-4-methyl-3-styrylpyridin-2(1<i>H</i>) ones 1/3 was described. In the presence of hydrochloric acid, the dichloromethane solution of 1 and 3 was protected by argon and irradiated with a 50 W LED at 410-415 nm for 2 h, giving 2-α, 2-β and 4-α, 4-β in good yields <i>via</i> a tandem reaction. The transformation involves a sequential <i>E</i>-to-<i>Z</i> photoisomerization, 6π-electrocyclization, and intramolecular nucleophilic addition-cyclization, enabling efficient construction of the dearomatized isoquinolin-1(2<i>H</i>)-one scaffold with high atom economy and bond-forming efficiency. Notably, the reaction exhibits excellent stereoselectivity, favoring <i>cis</i>-fused products, which are otherwise challenging to access <i>via</i> conventional thermal methods.