Total synthesis of dimeric Securinega alkaloids (-)-flueggenines D and I

We describe the total synthesis of (-)-flueggenines D and I. This features the first total synthesis of dimeric Securinega alkaloids with a C(alpha)-C(delta') connectivity between two monomeric units. The key dimerization was enabled by a sequence that involves Stille reaction and conjugate reduction. The high chemofidelity of the Stille reaction enabled us to assemble two structurally complex fragments that could not be connected by other methods. Stereochemical flexibility and controllability at the delta'-junction of the dimeric intermediate render our synthetic strategy broadly applicable to the synthesis of other high-order Securinega alkaloids.