Asymmetric Total Synthesis of Pre-schisanartanin C.

Pre-schisanartanin C belongs to the family of Schisandra nortriterpenoids with potent antihepatitis, antitumor, and anti-HIV activities. This paper presents the enantioselective total synthesis of pre-schisanartanin C (1). An important step in the total synthesis of 1 is gold-catalyzed intramolecular cyclopropanation of a 1,8-enyne substrate bearing a secondary ester group at the propargylic position to prepare a bicyclo[6.1.0]nonane core. Additional highlights include (i) an asymmetric Diels-Alder reaction to install the initial C5 stereogenic center of 1 and (ii) a sequential Pd-catalyzed Stille coupling, regio- and stereoselective Sharpless asymmetric dihydroxylation, and a subsequent intramolecular lactonization to construct the side chain of 1. The developed chemistry paves the way for the total syntheses of other family members bearing highly rigid bicyclo[6.1.0]nonane cores.