Synthetic Approaches to the Angucycline Antibiotics: A Synthesis of (±)-Hatomarubigin B and C.

The synthesis of the angucycline natural products hatomarubigin B and C in racemic form is described. The key step in the construction of the benz[a]anthraquinone skeleton of these molecules was the Diels–Alder reaction of the acetate of (E,1R*,5R*)-3-(2′-methoxyvinyl)-5-methylcyclohex-2-en-1-ol and 5-acetoxy-8-hydroxy-1,4-naphthoquinone. Methylation of the C11 phenolic group of the resulting cycloadduct, followed by aromatization of the B ring with subsequent deacylation gave (±)-hatomarubigin C. Oxidation of the latter compound with Dess-Martin periodinane, 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one, gave (±)-hatomarubigin B.