Stereospecific route to enantiopure all cis-2,3,6-trisubstituted piperidines. Facile synthesis of (−)-deoxocassine and (+)-azimic acid

Reduction of the enantiopure β-amino esters 10 provides the γ-amnio alcohol 11, which is condensed with 2,4-pentadione to afford 12. Stepwise cyclization of 12 produced the cyclic enamine 13, which is hydrogenated to deliver all cis-2,3,6-trisubstituted piperidine 14. Using this reaction sequence and subsequent Baeyer–Villiger oxidation as the key step (−)-deoxocassine and (+)-azimic acid are synthesized.