2-Allyloxybenzaldehydes undergo [2 + 1] cycloadditions under 365 nm LED irradiation to form the corresponding chroman-fused cyclopropanols.

Photochemical transformations of small molecules, such as ortho-substituted benzaldehydes, in the absence of a photocatalyst are significantly underexplored and may reveal unexpected outcomes. In the present paper, we showed that 2-(2-formylphenoxy)acetic acid and its esters undergo photocyclization into chromanone and benzofuranone derivatives under 365 nm irradiation. The reaction occurs exclusively in dimethyl sulfoxide and can be used to efficiently obtain hydroxychromanones in good yields (27–91%). A detailed mechanistic study revealed the clue of the divergent phototransformation with various products.

2-Acyloxybenzaldehydes are converted into 2-hydroxybenzofuranones in good to excellent yields (60–99%). The reaction proceeds at room temperature in DMSO upon 365 nm LED irradiation under photocatalyst-free conditions. The present atom-economical synthetic approach represents the aldehyde group umpolung reactivity.

A novel photoinduced umpolung strategy enabling the synthesis of 1,2-dicarbonyl compounds from simple salicylaldehyde derivatives is described.