Configurationally labile maleylacetone has been prepared by the careful hydrolysis of 4- acetonylidenebut-2-ene-4-olide (2) and shown to exist as a mixture of closed “pseudo” acid 4a and open enol acid 4b in chloroform and benzene and as “pseudo” acid in water. Ultraviolet and nmr spectra of the acids and anions are reported along with dissociation constants of the acid.
