Diterpenoids. XII. Catalytic Hydrogenation of Δ^{5, 6}-and 6-Enol Acetoxyhydrofluorene Derivatives. A Synthesis of Hydrofluorene Derivatives (cis-A/B-Ring Fusion (α C₅-H))

Abstract

Hydrofluorene (III) and (IV) prepared by alkaline treatment of cis-dioxo ester (II), was already considered, without reliable evidence, to have cis-A/B-ring fusion. Now, in comparison with standard trans-hydrofluorene (XII) previously reported, the assumption on the structure of IV has been confirmed. Otherwise, stereochemical analysis on catalytic hydrogenation of Δ^{5, 6}-unsaturated hydrofluorene (XIV and XV) is also carried out.