| Abstract
| - The Pummerer reaction of imidosulfoxides bearing tethered alkenyl groups has been employed forthe synthesis of several alkaloids. The required imidosulfoxides necessary for the cascade sequencewere easily obtained by heating the appropriate amide with (ethylsulfenyl)acetyl chloride followedby sodium periodate oxidation. The initially formed thionium ion, obtained by treating theimidosulfoxide with acetic anhydride and p-toluenesulfonic acid, reacts with the neighboring imidogroup, and the resulting oxonium ion undergoes subsequent deprotonation to produce anisomünchnone dipole. This mesoionic betaine intermediate undergoes ready intramolecular dipolarcycloaddition across the neighboring π-bond. Exposure of the resulting cycloadducts to additionalacetic anhydride leads to ring opening and formation of a 5-acetoxy-substituted 2(1H)-pyridone.This six-ring heterocyclic system constitutes a valuable building block for the synthesis of a varietyof pyridine, quinolizidine, and clavine alkaloids. The cyclization−deprotonation−cycloadditioncascade has been successfully applied to the synthesis of the naturally occurring alkaloids onychnine,dielsiquinone, (±)-lupinine, (±)-anagyrine, (±)-pumiliotoxin C, and (±)-costaclavine.
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