Iodine → (R)-tert-butyl 3-((S)-1-(3-chloro-2-fluorophenyl)-1-hydroxy-5-methoxypentyl)piperidine-1-carboxylate

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Reaction Steps

A flame dried 250 mL three-necked flask was charged with magnesium turnings (7.02 g, 0.293 mol), a small crystal of iodine and THF (30 mL). The flask was evacuated and refilled with N2. A solution of 1-chloro-4-methoxybutane (28.69 g, 0.234 mol) in THF (120 mL) was added dropwise slowly to the mixture. The reaction mixture was stirred under reflux for 2.5 h and most of magnesium was consumed. The resulting Grignard reagent was used as follows To another 100 mL three-necked flask was added (R)-tert-butyl 3-(3-chloro-2-fluorobenzoyl)piperidine-1-carboxylate (10 g, 0.0293 mol) and THF (100 mL). The flask was evacuated and refilled with N2. The mixture was cooled with dry ice-acetone bath and the Grignard reagent (250 mL) was added. The reaction mixture was allowed to warm slowly to rt while stirring overnight. The mixture was quenched with satd aq NH4Cl (50 mL), extracted with EtOAc (3×), and the combined organic layers were dried over Na2SO4. Evaporation of the solvent gave the crude product. The LC-MS analysis of the crude product indicated the presence of two isomers (95:5). Flash column chromatography, eluting with 10% EtOAc/PE afforded (R)-tert-butyl 3-((S)-1-(3-chloro-2-fluorophenyl)-1-hydroxy-5-methoxypentyl)piperidine-1-carboxylate (9.4 g, 75% yield). 1H NMR (400 MHz, DMSO): 0.68 (m, 1H), 1.50-1.01 (m, 7 H), 1.37 (s, 9H), 1.75 (m, 2H), 2.01 (m, 1H), 3.11 (s, 3H), 3.17 (m, 2H), 3.85 (m, 1H), 7.2 (t, 1H), 7.45 (m, 2H). MS (E/Z): 430 (M+H+).

Provenance & Evidence