Asymmetric Total Synthesis of the Highly Strained 4β-Acetoxyprobotryane-9β,15α-diol

The first and asymmetric total synthesis of 4β-acetoxyprobotryane-9β,15α-diol, containing a rare and highly strained trans-fused bicyclo[3.3.0]octane ring system, has been achieved. The synthetically challenging [6-5-5] tricyclic ring system in the final product was efficiently and diastereoselectively synthesized via an asymmetric rhodium-catalyzed [4 + 2] cycloaddition reaction, followed by a unique benzilic acid type rearrangement under very mild conditions. The seven contiguous stereocenters were installed efficiently and diastereoselectively.