Intramolecular formal aza-[3+3] cycloaddition approach to indoloquinolizidine alkaloids.: A stereoselective total synthesis of (±)-tangutorine

A 19-step stereoselective total synthesis of (+/-)-tangutorine is described here. The total synthesis features an intramolecular aza-[3 + 3] formal cycloaddition strategy and also a Heck coupling for constructing the C2-C3 bond. This work provides a novel approach toward the indoloquinolizidine family of alkaloids.