1,3-Dialkylnaphtho[2,3-c] furan-4,9-diones were obtained by the Friedel-Crafts reaction of phthalic anhydride with 2,5-dialkylfurans. The reaction of phthalic anhydride with 2-acetyl-5-methylfuran, instead of 2,5-dialkylfurans, produced 2-methylnaphtho[2,3-b] furan-4,9-dione. The application of this method to the synthesis of 8-hydroxynaphtho [2, 3-b] furan-4, 9-dione [isodiodantunezone] is also described.