Asymmetric Total Synthesis of (–)-trans-Blechnic Acid via Rhodium(II)-Catalyzed C–H Insertion and Palladium(II)-Catalyzed C–H Olefination Reactions

An asymmetric total synthesis of (-)-trans-blechnic acid, a dihydrobenzofuran neolignan, has been achieved. The key steps involve an elaboration of the cis-2,3-dihydrobenzofuran core structure by enantio- and diastereoselective intramolecular C-H insertion using dirhodium(II) tetrakis[N-phthaloyl-(R)-tert-leucinate] [Rh-2(R-PTTL)(4)] and a direct coupling of an acrylate unit with the core structure employing Yu's palladium(II)-catalyzed intermolecular C-H olefination.