Photo-oxidation of tanshinone II (6,7,8,9-tetrahydro-1,6,6-trimethylphenanthro[1,2-b]furan-10,11-dione)

Irradiation of the phenanthrofurandione tanshinone II (2) with u.v. light in the presence of air afforded 9-hydroxytanshinone (1), which had been isolated from a Chinese drug as a minor constituent. Two other products, an anhydride (3) and a lactone (4), were also obtained. The formation of these compounds was explained in terms of an intermediate 9,10-epidioxide (6), derived from tanshinone II by photoenolization and oxygenation.