Lactams. XXIV. Alkaline hydrolysis of 1-benzyl-2-piperidone derivatives: application to cis-trans isomerization of the 5-ethyl-2-oxo-4-piperidineacetic acid system

In boiling 2.5 N solution of KOH in 40% (w/w) aqueous EtOH, the lactams (±)-5a, b, d were hydrolyzed to an extent of 75-98% within 8-20 h, attaining equilibrium with the corresponding ω-amino acid derivatives (±)-6a, b, d. The potassium salt (±)-8,generated in situ from the translactam acid (±)-7,was equilibrated with the ring-opened product (±)-6f and the recyclized cis isomer (±)-5f in a ratio of 57 : 15 : 28 within ca. 45 h under similar reaction conditions. The cis-N-(2-arylethyl) analog (-)-9 was converted into the trans-lactam acid (+)-13,a key synthetic precursor for the 8-hydroxy-9,10-dimethoxybenzo [a] quinolizidine-type Alangium alkaloids, through application of such alkaline hydrolytic cis-trans equilibration followed by debenzylation