Total Synthesis of Scytonemin and Reduced Scytonemin.

A total synthesis of scytonemin and reduced scytonemin was achieved. The intramolecular Mannich reaction between the aminal group and the siloxy olefin, derived from the aldol adduct between isatin and TIPS-protected raspberry ketone, proceeded to give a tricyclic half-scytonemin skeleton. After dimerization to construct the scytonemin skeleton, oxidation with t-BuOCl provided olefins in side chains regio- and stereoselectively in high yield. Treatment of the product with DDQ afforded the scytonemin skeleton in a quantitative yield. Interconversion between protected scytonemin and protected reduced scytonemin was achieved, which could be developed as molecular machines. Additionally, the cyclic voltammetry of reduced scytonemin was disclosed.