Total Synthesis of an Atropisomer of the Schisandra Triterpenoid Schiglautone A.

A diastereoselective approach for the total synthesis of an unusual atropisomer of the Schisandra triterpenoid (±)-schiglautone A is described. The efficient synthetic strategy features three key transformations: 1) two sequential titanium(III)-catalyzed radical cyclization/homologation reactions to construct the trans-fused [6,7] bicycle as well as install the quaternary carbons at C10 and C14 with the desired stereochemistry; 2) a Claisen rearrangement followed by a ring-closing metathesis to forge the strained nine-membered ring; and 3) a substrate-controlled Michael addition to enable the introduction of the C17 side-chain with good diastereoselectivity.