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.