Flexible synthetic routes to poison- frog alkaloids of the 5,8-disubstituted indolizidine- class I: synthesis of common lactam chiral building blocks and application to the synthesis of (-)-203A, (-)-205A, and (-)-219F

• Naoki Toyooka,
• Dejun Zhou,
• Hideo Nemoto,
• H. Martin Garraffo,
• Thomas F. Spande and
• John W. Daly

Beilstein J. Org. Chem. 2007, 3, No. 29, doi:10.1186/1860-5397-3-29

• protected hydroxymethyl side-chain (Figure 2). The synthesis began with the known piperidone 3, [15] which was treated with n-BuLi and then CbzCl to provide the Cbz-urethane 4. Treatment of 4 with LiHMDS followed by 2-[N,N-bis(trifluoromethylsulfonyl)amino]-5-chloropyridine (Comins' reagent) [16] gave the