Some 2,6- and 2,7-disubstituted naphthazarins have been synthesized by cyclizing the corresponding β-(2,5-dimethoxybenzoyl)-acrylic acids. With one exception, it was established that isomerization does not occur and therefore that the method provides unambiguous proof of structure for these naphthazarins. Conversely, the procedure was used to determine the positions of the chlorine atoms in two β-(2,5-dimethoxybenzoyl)-chloroacrylic acids.