Optimization of a Visible-Light-Mediated Iodocyclization of Juglone

Visible-light-mediated reactions has emerged as a sustainable tool in organic synthesis, enabling transformations under mild conditions in accordance with green chemistry principles.¹ In this context, applying this protocol to the functionalization of naphthoquinones could offer a valuable synthetic approach for accessing structurally diverse, high-value-added molecules. Based on these principles, this work aimed to optimize the iodocyclization juglone, a naturally occurring 1,4-naphthoquinone,² under visible light.
Juglone 1 was first treated with allyl bromide and Ag₂O in DCM at room temperature for 68h, affording compound 2 in 76% yield (Figure 1a).³ Subsequently, the resulting intermediate 2 underwent a Claisen rearrangement in DPE at 160 ºC for 24 h, producing reallyl juglone 3 in 60% yield.⁴ The iodocyclization was then optimized by evaluating light sources, solvents, and additives. The best conditions employed blue LED (50 W), SnCl₄ (200 mol%), and DCM, affording the iodinated intermediate 4 in 94% yield after 1h (Figure 1b).