Reactions of 1,4-naphthoquinone and 5-hydroxy-1,4-naphthoquinone with ninhydrin

1,4-Naphthoquinone and 5-hydroxy-1,4-naphthoquinone react with ninhydrin to give 2-(2-hydroxy-1,3-dioxo-2,3-dihydro-1H-inden-2-yl)naphthalene-1,4-dione and 8-hydroxy- 2-(2-hydroxy-1,3-dioxo-2,3-dihydro-1H-inden-2-yl)naphthalene-1,4-dione, respectively.