Green photochemistry: solar-chemical synthesis of Juglone with medium concentrated sunlight

Dye sensitized photooxygenations of 1,5-dihydroxynaphthalene were investigated with soluble and solid-supported sensitizers and moderately concentrated sunlight. Moderate to good yields up to 79% of 5-hydroxy-1,4-naphthoquinone (Juglone) were achieved on multiple gram-scales after just 4 h of illumination. The mild and environmentally friendly reaction conditions make this application particularly attractive for 'green photochemistry'.