First Enantioselective Synthesis of Dendrobatid Alkaloids Indolizidine (-)-209I and (-)-223J

Dieter Enders; Christoph Thiebes

doi:10.1055/s-2000-8675

Synlett 2000; 2000(12): 1745-1748
DOI: 10.1055/s-2000-8675

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First Enantioselective Synthesis of Dendrobatid Alkaloids Indolizidine (-)-209I and (-)-223J

Dieter Enders^* , Christoph Thiebes

^*Institut für Organische Chemie, Rheinisch-Westfälische Technische Hochschule, Professor-Pirlet-Straße 1, D-52074 Aachen, Germany; Fax +49(241)8 88 81 27; E-mail: Enders@RWTH-Aachen.de

Abstract

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The first asymmetric synthesis of dendrobatid indolizidine alkaloids (-)-209I [(5R,8R,8aS)-1a] and (-)-223J [(5R,8R,8aS)-1b] via a common late-stage intermediate amino nitrile (5R,8R,8aS)-2 are described. Amino nitrile 2 was synthesized employing the highly diastereoselective 1,2-addition of an organocerium reagent to α-substituted aldehyde RAMP-hydrazone (R,R)-9, which was in turn prepared in two steps starting from n-pentanal. The hydrazine obtained in this way was converted to pyrrolidine (R,S)-13, from which amino nitrile (5R,8R,8aS)-2 was obtained. Indolizidines (-)-209I and (-)-223J (de = 96 - 99%, ee > 99%) and their C-5 epimers (5S,8R,8aS)-1a,b were prepared from 2 by alkylation/stereoselective reduction and stereoselective Bruylants reaction, respectively.

asymmetric synthesis - alkaloids - indolizidines - hydrazones - amino nitriles

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