Enantioselective synthesis of tetraponerines by Pd- and Ru-catalyzed domino reactions

An enantioselective synthesis of tetraponerines T4, T6, T7, and T8 in 24-36% overall yield is described. Key steps in this synthesis are a Pd-catalyzed domino allylation and a Ru-catalyzed ring rearrangement. The effect of different substituents on the equilibrium of the metathesis rearrangement has been investigated. To complete the synthesis a sequence of Wacker oxidation and Takai olefination was used. The preparation of four representative tetraponerines differing in stereochemistry, ring size, and side chain employing five metal-organic reactions clearly demonstrates the efficiency of transition metals in organic synthesis.