Synthesis of the monomeric unit of γ-actinorhodin

Abstract

The first syntheses of the monomeric units of actinorhodin 19 and 5-epi-γ-actinorhodin 18 are described. The key steps involve addition of 2-trimethylsilyloxyfuran 14 to the 2-acetylnaphthoquinone 13 affording the adduct 15 which undergoes oxidative rearrangement to a pyranonaphthoquinone system 16 upon treatment with ceric ammonium nitrate. Naphthoquinone 13 is prepared from naphthol 11 which, in turn, is prepared via addition of furan 5 to 1,4-dimethoxy-2,3-dehydrobenzene followed by treatment with acid.