Total syntheses of (±)-21-oxogelsemine (3) and (±)-gelsemine (1) are described. Free radical cyclizations play important roles in constructing the tricyclic core (40 → 41) and oxindole (93 → 96) substructures of the target alkaloids, and an isomerization−cyclization strategy (101 → 102) was used to complete construction of the gelsemine cage. Observations made along the way include intramolecular 1,4- and 1,6-hydrogen atom transfers (64 → 65 and 40 → 47) and a free radical cyclization-fragmentation sequence (85 → 86 + 87). A retroaldol−aldol strategy for adjusting oxindole stereochemistry in gelsemine-like structures is also described (72 → 74 and 86 → 87).

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Free Radical Cyclizations in Alkaloid Total Synthesis: (±)-21-Oxogelsemine and (±)-Gelsemine. -The key steps in the synthesis of the title compounds (XV) and (XVI) are radical cyclizations of the thio derivative (VI) and the carboxanilide (XI) and isomerization-cyclization of the aldehyde (XIII) . -(ATARASHI, S.; CHOI, J.-K.; HA, D.-C.; HART, D. J.; KUZMICH, D.; LEE, C.-S.; RAMESH, S.; WU, S. C.; J. Am. Chem. Soc. 119 (1997) 27, 6226-6241; Dep. Chem., Ohio State Univ., Columbus, OH 43210, USA; EN)