Pigments of Fungi. XXIII. Approaches Towards (±)-Austrocortirubin From 3-Methyl-1-trimethylsilyloxybuta-1,3-diene

Abstract

The products (5) and (21) of cycloaddition between 3-methyl-1-trimethylsilyloxybuta-1,3-diene (3) and naphthazarin (4), and between (3) and the naphthopurpurin acetal (2), respectively, are converted into the tetrahydroanthraquinones (16)-(18), (26) and (27) via a series of intermediate epoxy alcohols. Stereochemical assignments are corroborated by a single-crystal X-ray structure analysis of the bromohydrin (16). The tetrahydroanthraquinones (27) and (18), advanced intermediates in a proposed synthesis of the fungus pigment austrocortirubin (1) and its 6-demethoxy analogue (20), respectively, are resistant to efficient dehalogenation.