Synthetic Study of Linderol A, a Potent Inhibitor of Melanin Biosynthesis

We found two novel skeleton rearrangement reactions. The one was the reaction from coumarin derivatives having an electron-withdrawing group at the 3-position with dimethylsulfoxonium methylide to cyclopenta[b]benzofuran derivatives. The other was the reaction from benzo[b]cyclobuta[d]pyran derivatives having an electron-withdrawing group at the 2a-position to tetrahydrodibenzofuran derivatives. Interestingly, the latter reaction proceeded stereoconvergently regardless of the stereochemistry at the 1-position in the cyclobutane compounds. Driving forces of these reactions would be attributable to release of the ring strain including in a cyclopropane ring and cyclobutane ring. These methodologies were applied to the total synthesis of linderol A, which is a constituent of Lindera umbellata (Lauraceae) and has a potent inhibitory activity on melanin biosynthesis, and the synthesis was performed in 14 steps, 34% overall yield. Furthermore, the uncertain absolute structure of linderol A was determined, and its asymmetric synthesis was also achieved.