Construction of α-quinonyl-α-hydroxy/amino acid esters through the redox chain reaction.

Although quinones, α-hydroxy acids and α-amino acids are all widely used organic compounds in numerous fields, compounds based on the combination of these motifs were underexplored. In this study, the direct hydroxyalkylation of quinones with glyoxylates was developed through a redox chain reaction using SnCl2 as the reductive initiator and catalyst, and AlCl3 as the co-catalyst. Various α-quinonyl-α-hydroxyacetyl esters were obtained under mild conditions in up to 81% yield within a few hours. Substrates with different ester groups were accessed through in situ oxidation of corresponding tartrates to glyoxylates by PIDA. Moreover, aminoalkylation of quinones was achieved by the multicomponent reaction of quinones, glyoxylates and amides, affording a series of α-quinonyl-α-aminoacetyl esters in up to 80% yield. The products were easily converted to unnatural amino acids, aryl azo compounds and peptides as demonstrations of their wide potential applications.