s-Indacene-1,3,5,7(2H,6H)-tetraone (‘Janusdione’) and 1,3-Dioxo-5,6-indanedicarboxylic Acid: Old and New 1,3-Indandione Derivatives

Efficient syntheses, X-ray structures and spectroscopic properties of s-indacene-1,3,5,7(2H,6H)-tetraone (1) and 1,3-dioxo-5,6-indanedicarboxylic acid (2), their precursors and derivatives, are described for the first time.