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. (C) 2007 Elsevier Ltd. All rights reserved.