Concise Syntheses of bis-Strychnos Alkaloids (−)-Sungucine, (−)-Isosungucine, and (−)-Strychnogucine B from (−)-Strychnine

The first chemical syntheses of complex, bis‐Strychnos alkaloids (−)‐sungucine (1), (−)‐isosungucine (2), and (−)‐strychnogucine B (3) from (−)‐strychnine (4) is reported. Key steps included (1) the Polonovski–Potier activation of strychnine N‐oxide; (2) a biomimetic Mannich coupling to forge the signature C23−C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH3CN‐mediated reduction to fashion the ethylidene moieties in 1–3. DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners. Alkaloids time! The first chemical syntheses of complex, bis‐Strychnos alkaloids (−)‐sungucine, (−)‐isosungucine, and (−)‐strychnogucine B from (−)‐strychnine is reported (see scheme). DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners.