3-Halogeno-4-methoxyphenylpropiolic acids are converted by acetic anhydride into a mixture of 6- and 8-halogeno-7-methoxy-1-(3-halogeno-4-methoxyphenyl)naphthalene-2,3-dicarboxylic anhydrides.

The structure of 6-bromo-7-methoxy-1-(3-bromo-4-methoxyphenyl)naphthalene-2,3-dicarboxylic anhydride was established by its conversion into the corresponding 6,7-dimethoxy derivative. The structure of the remaining anhydrides were established by i.r. and u.v. spectroscopy.

The anhydrides are isomerised by aluminium chloride to the corresponding 7H-benzo[c]fluoren-7-one.