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Synthesis 1997; 1997(10): 1151-1160
DOI: 10.1055/s-1997-3185
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Enantioselective Syntheses of 2-Alkyl-, 2,6-Dialkylpiperidines and Indolizidine Alkaloids Through Diastereoselective Mannich-Michael Reactions

Markus Weymann, Waldemar Pfrengle, Dieter Schollmeyer, Horst Kunz*
  • *Institut für Organische Chemie, Universität Mainz, D-55099 Mainz, Germany, Fax +49(6131)394786; E-mail: hokunz@goofy.zdv.uni-mainz.de
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Publication History

Publication Date:
31 December 2000 (online)

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Aldimines of 2,3,4,6-tetra-0-pivaloyl-β-D-galactosylamine react with 1-methoxy-3-trimethylsilyloxybuta-1,3-diene in a Mannich-Michael condensation reaction sequence to give 2-substituted N-galactosyl-5,6-dehydropiperidin-4-ones 3 with high diastereoselectivity. The X-ray analysis of the 2-propyl derivative 3a proved (R)-configuration of the major diastereomer and led to the correction of our earlier assignment of configuration for (-)-coniine hydrochloride 9a obtained from this intermediate. Despite their low reactivity, these enaminones 3 can be converted into chiral 2,6-cis-disubstituted piperidinones 12 with high stereoselectivity by reaction with organocuprates in combination with hard electrophiles. Enantiomerically pure alkaloids such as (-)-dihydropinidine and gephyrotoxine 167B have been synthesized according to this methodology.

asymmetric synthesis - tandem Mannich-Michael reaction - 1,4 addition to enaminones - piperidine alkaloids - configuration of (R)-coniine