Synthesis of naturally occurring rubilactone, mollugin, and dihydromollugin of Rubia cordifolia

Rubilactone (1), dihydromollugin (2), and mollugin (3) are naturally occurring products found in Rubia cordifolia, which is a famous Chinese herb with antitumor, viral inhibition and other activities. Synthetic studies were carried out in these naphthoic acid esters starting from 1,4-dihydroxy-2-naphthoic acid. In this study, we finished the synthesis of rubilactone which has not been reported before and also synthesized dihydromollugin and mollugin with better yields with different approaches compared to those previously reported in the literature.