Abstract
Two approaches to enantiopure 4-oxo- and 4-( R)-hydroxypipecolic acid derivatives from protected L-aspartic acid were developed. The first route exploits an intramolecular Michael addition on the stable enaminone 8. Hydrogenation and concomitant decarboxylation gave the 4-oxo derivative 11 which was reduced selectively to the 4-( R)-hydroxy derivative 12. The second route starts with a Michael addition followed by an intramolecular Dieckmann condensation to build the piperidine ring. The 4-oxo derivatives 11 and 19 are thus obtained in an expeditious manner on large scale without any chromatographic purification. Both sequences proved to be highly stereoselective.
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