Process for Production of Piperidine Derivatives Note

Patent Process for Production of Piperidine Derivatives (Note 1) 

D Ambra etal, US Patent 6,458,958 (October 1, 2002) Assignee Albany Molecular Research, Inc. 

A mixture of 4-bromophenylacetic acid (0.800 mol), 2-amino-2-methyl-l-propanol (1.20 mol) and 900 ml xylenes were refluxed for 24 hours, cooled, filtered, and concentrated. Precipitated crystals were slurried in hexanes and the product isolated in 75% yield. 

Potassium hexamethyldidisilazide (0.0279 mol) was added to the product from Step 1 (0.0186 mol) dissolved in 50 ml THF, the mixture stirred 15 minutes at ambient temperature, and methyl iodide (0.0186 mol) added. After stirring 1 hour, a second equivalent of potassium hexamethyldidisilazide and methyl iodide were added, stirred 1 hour, and an additional 0.2 ml methyl iodide then added. The mixture was quenched with 100 ml 10% HO Ac in water and extracted with CHjClj. The extract was washed with brine, dried, concentrated at ambient temperature at 0.1 mm Hg, and a residue obtained. The solid was slowly dissolved in 30 ml isopropyl alcohol containing 20 ml water until an oil formed. Thereafter, an additional 5 ml isopropyl alcohol was added with heating and the re-crystallized product isolated in 84% yield. 

The product from Step 2 (0.0338 mol) was dissolved in 400 ml THF, cooled to —78 °C, n-butyllithium (0.042 mol) added, and the mixture stirred at —78 °C for 30 minutes. Thereafter, N,N-dimethylcyclopropyl-carboxylic acid amide (0.102 mol) dissolved in 30 ml THF was added and the mixture stirred 30 minutes. It was slowly warmed to -15°C, quenched with water, extracted with CH2CI2, and concentrated. The residue was cooled to 0 °C, treated with acetonitrile, filtered, and the product isolated in 72% yield. 

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