Anodic Oxydation of Heterocycles: Alkaloids Synthesis
The reductive amination of appropriate ketopyrrolidines leading to 3,5-dialkylindolizidines usually gives stereoselectively the indolizidine with a cis relative stereochemistry on the piperidine moiety. We report herein unexpected results concerning the effect of the nature of the C3 subsiituent on this stereoselectivity.
KeywordsAcetyl Chloride Reductive Amination Ester Moiety Chiral Building Block Carbomethoxy Group
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References and notes
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- 5.Célimène, C.; Dhimane, H.; LeBail, M.; Lhommet, G. Tetrahedron Lett. 1994, 35,6105.Trans and cis isomers of 1 were not separable by chromatography.Google Scholar
- 6.Reduction of 1 was carried out by using NaBH4/CaCl2 system in THE/EtOH (1/1). At this stage the pure trans alcohol 2 was isolated in 67% yield. Acetate 3 was prepared from 2 using acetyl chloride in pyridine (92% yield).Google Scholar
- 7.Epimers 6 were isolated by column chromatography (Si02, Et20/Pentane, 3/1).Google Scholar
- 8.The key intermediate 1 could not be separated from its cis isomer (4%) and therefore 5 was used as a trans/cis (96/4) mixture.Google Scholar
- 9.Product 7b was purified by column chromatography (Si02, Et20/Pentane, 3/1)Google Scholar
- 10.The two others stereomers were present in too low concentration to be isolated.Google Scholar
- 11.The ester moiety reduction was performed at -78°C using LiAIH4 in THF.Google Scholar
- 12.This acetate was obtained by refluxing 9 in THF in the presence of Ac20 (1.1 equiv.) and Et3N (4 equiv.). Otherwise Ac20/Pyridine or Ac20/DCC/DMAP left 9 unchanged. The use of AcCI instead of Ac20 gave a complex mixture.Google Scholar