Russell, G. A., Myers, C. L., Bruni, P., Neugebauer, F. A., & Blankespoor, R. (1970).
Semidiones. X. Semidione radical anions derived from indan-2,3-dione, coumaran-2,3-dione, thianaphthalenequinone, isatin,
and N-hydroxyisatin. Nitroxide radicals derived from isatin, dioxindole, oxindole, and other indole derivatives.
Journal of the American Chemical Society, 92(9), 2762-2769. doi:10.1021/ja00712a029.