Preparation of Trans‐5‐Hydroxy‐l‐Pipecolic Acid and Cis‐4‐Hydroxy‐l‐Pipecolic Acid from l‐Baikiain (1, 2, 5, 6‐l‐Tetrahydropyridine‐2‐Carboxylic Acid)

Z‐trans‐5‐OH‐L‐pipecolic acid together with Z‐cis‐4‐OH‐L‐pipecolic acid is obtained in a 7:3 ratio by reduction of the oxymercuration product of Z‐L‐baikiain (Z‐1, 2, 5, 6‐L‐tetrahydropyridine‐2‐carboxylic acid). The opposite composition ratio is obtained using mercuric trifluoroacetate, thus giving access to the preparation of either of the two isomers.