Abstract
A quantitative analytical study to determine the isomer ratios of the 6-piperidones (type 7) and 2-piperidones (type 5) produced by the mercuric acetate-edetic acid (EDTA) oxidation of 1-(2-aryl-2-hydroxyethyl)-3-alkylpiperidines (±)-4c, d, f, h, 4e, g, i, j, and (±)-38 was carried out. It has been found that all the substrates with a benzyloxy group in the aryl moiety, regardless of its location, undergo oxidation at the 6-position preferentially as compared with the debenzyloxy derivatives such as (±)-4a, b. Comparison of the quantitative data from 4e and (±)-4f with those from (±)-4b indicated that the cis acetate chain at the 4-position increases the extent of the 6-oxidation, whereas a trans acetate chain at the same position has little effect. These two factors enhance the practical value of the "cincholoipon-incorporating method" for chiral syntheses of the 1-type Alangium alkaloids, in which the mercuric acetate-EDTA oxidation of 4e, g, i, j to the 6-piperidones (type 3)is one of the key synthetic operations.
