Concise syntheses of eburnane indole alkaloids

The asymmetric divergent syntheses of a group of C20 ethyl oxo-functionalized eburnane alkaloids, (-)-eburnaminol (5), (+)-larutenine (6), (-)-terengganensine B (7), (-)-strempeliopine (8), and (-)-terengganensine A (9), have been achieved. The key step in the assembly of the complex ring system of the target molecules is a photoredox catalytic nitrogen-centered radical cascade reaction, which allows the regioselective and stereoselective construction of the B, C, and D rings and the installation of the C21 chirality of the eburnane alkaloid skeleton in one pot.