S. Kafka et al., Novel ring contraction of 3-hydroxy-2,4(1H,3H)-quinolinediones in aqueous alkali. The first convenient route to 2-hydroxyindoxyls, J ORG CHEM, 66(19), 2001, pp. 6394-6399
Ring contraction of 3-hydroxy-2,4(1H,3H)-quinolinediones (1) in aqueous pot
assium hydroxide resulted in the formation of 2-hydroxyindoxyls and/or diox
indoles. The choice of N-substituent and the reaction conditions govern the
chemoselectivity of the reaction. N-Phenyl-substituted derivatives 1 give
2-hydroxyindoxyls, while N-alkyl- and N-benzyl-substituted derivatives affo
rd the corresponding dioxindols. On the basis of byproduct analysis, as wel
l as independent experiments, the most plausible reaction mechanism is prop
osed.