Total Synthesis of (-)-Antroalbocin A Enabled by a Strain Release-Controlled Photochemical 1,3-Acyl Shift.

The first bioinspired, enantioselective, and protecting group free total synthesis of the antibacterial sesquiterpenoid (-)-antroalbocin A ( 1 ) has been achieved in 12 steps (5.4% overall yield) from dimedone. An organocatalytic Robinson annulation gave rapid access to the tricyclic enone ( 19 ) as starting material for the photochemical domino process of deconjugation and sigmatropic 1,3-acyl shift. Computational data of this process indicate that the 1,3-acyl shift benefits from the highly strained 1,3-enone 8 . The transformation of 8 to its bridged isomer 5 is exergonic and, therefore, enables an increased conversion compared to unstrained substrates.