Light-induced O-to-C 1,4-carbonyl transposition in salicylaldehyde derivatives: umpolung synthesis of 1,2-dicarbonyl compounds and beyond

A novel photoinduced umpolung strategy enabling the synthesis of 1,2-dicarbonyl compounds from simple salicylaldehyde derivatives is described. This method provides α-ketoesters and α-ketoamides in excellent yields (79-90%) under mild photocatalyst-free conditions (DMSO, room temperature). Amides, bearing a dimethylamino group, are able to undergo subsequent steps in a cascade photoprocess involving the Norrish-Yang reaction, which leads to the formation of oxazolidin-4-ones and azetidin-2-ones. The obtained 1,2-dicarbonyls were further utilized in the synthesis of benzimidazole, quinoxalinone, and benzofuran derivatives involving non-photochemical transformations.