Synthesis of alkylated indolizidine alkaloids via Pummerer mediated cyclization: synthesis of (±)-indolizidine 167B, (±)-5-butylindolizidine and (±)-monomorine I

The syntheses of indolizidine alkaloids, i.e., (±)-coniceine, (±)-indolizidine 167B, (±)-5-butylindolizidine and (±)-monomorine I via Pummerer cyclization are described. The key step is the transformation of lactam sulfoxide to bicyclic lactam via the Pummerer cyclization.