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)

Abstract

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.

Stereoselective Introduction of Hydroxyl Group to Piperidine Ring using Electrochemical Method

“…(Shinwa Chemical Industries, Ltd. HR-1, 0.25mmφ x 25m, 190 o C): cis-3a/trans-3a = 25/75 (retention time: 9.4 min and 8.7 min, respectively) (YMC-SIL, 4.6mmφ x 15cm, i-PrOH/n-Hexane = 1/50, detected at 210nm, 1.0mL/min): cis-3b/trans-3b = <1/99 (retention time: 42.5 min and 38.0 min, respectively) (YMC-SIL, 4.6mmφ x 15cm, EtOH/n-Hexane = 1/50, detected at 210nm, 1.0mL/min): cis-3c/trans-3c = 29/71 (retention time: 39.4 min and 41.0 min, respectively) trans-3b: 9) colorless oil; IR (neat) 3950,2953,1740,1697,1430,1250,1219,1149,1122,1018, 771 cm -1 ; 1 H-NMR (300MHz) (CDCl 3 )δ7. 43-7.23 (m, 5H), 5.25-5.08 (m, 2H), 5.08-4.96 (m, 0.55H), 4.96-4.86 (m, 0.45H), 4.22-3.93 (m, 2H), 3.74 and 3.70 (2s, ECS Transactions, 2 (22) 7-18 (2007) hexane/EtOAc = 20/1).…”