Asymmetric Total Syntheses of Megacerotonic Acid and Shimobashiric Acid A

The asymmetric total syntheses of the alpha-benzylidene-gamma-butyrolactone natural products megacerotonic acid and shimobashiric acid A have been accomplished in nine and 11 steps, respectively, from simple, commercially available starting materials. The key step for each synthesis is the (arene)RuCl(monosulfonamide)-catalyzed dynamic kinetic resolution-asymmetric transfer hydrogenation (DKR-ATH) of racemic alpha,delta-diketo-beta-aryl esters to establish the absolute stereochemistry. Intramolecular diastereoselective Dieckmann cyclization forms the lactone core, and ketone reduction/alcohol elimination installs the alpha-arylidene.