Total Synthesis of Aspidofractinine Alkaloid Paucidirinine.

The first total synthesis of paucidirinine (1d), a highly congested aspidofractinine alkaloid containing a special contracted five-membered lactam ring, was achieved in 10 steps with 8% overall yield from commercially available materials. Several key maneuvers, including tandem enamination/[4 + 2] cycloaddition reaction and SmI2-promoted radical cyclization, were featured in this potentially scalable strategy.