Stereoselective Reactions. VIII. Stereochemical Requirement for the Benzylic Oxidation of Lignan Lactone. A Highly Selective Synthesis of the Antitumor Lignan Lactone Steganacin by the Oxidation of Stegane

A highly efficient synthesis of the antitumor steganin lignan steganacin (1) was accomplished. Bromination of stegane (7) with N-bromosuccinimide followed by treatment with aqueous tetrahydrofuran afforded steganol (3) in 85% yield. Acetylation of 3 gave 1 in 72% yield. Stegane (7) was also oxidized with 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone in AcOH to give 1 directly in 10% yield. Stereochemical requirements for the benzylic oxidation of dibenzocyclooctadiene lignan lactones are discussed.