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US20030232833


Preparation of N-Benzyl-3,3-dimethyl-4-piperidone. 26

In a 1 liter 3-neck flask equipped with a mechanical stirrer, an addition funnel and a calcium chloride drying tube was added a 37% weight solution of formaldehyde (168.5 mL, 2.25 mole) dissolved in 500 mL of absolute ethanol. The resulting solution was cooled in an ice-water bath to 10.degree. C., and benzylamine (109 mL, 1 mole) was added dropwise over a one hour period. In a separate 3-liter 3-neck flask equipped with a mechanical stirrer, an addition funnel and two condensers was added 3-methyl-2-butanone (113 mL, 1.06 mole) dissolved in 500 ml of absolute ethanol and concentrated hydrogen chloride (92 mL, 1.11 mole). The resulting solution was brought to reflux and the formaldehyde/benzylamine solution is added dropwise over a 2 hour period. This solution was heated at reflux overnight, and then cooled to ambient temperature. Diisopropylethylamine (142.2 g, 1.1 mole) and formaldehyde (22.46 mL, 0.3 mole) were added and the resulting solution was heated to reflux for six hours, and then cooled to ambient temperature. The solution was quenched with potassium hydroxide (61.6 g, 1.1 mole) in 200 mL of water, and then extracted 3 times with 500 ml ethyl acetate. The organic layers were concentrated under vacuum to give 225 g of a red oil. The crude oil was dissolved in 1 liter of methylene chloride. This solution was carefully poured over 1 kg of silica gel on a sintered glass filter. The silica gel was washed with 4 L of methylene chloride. The methylene chloride was concentrated under vacuum to provide 142 g of a yellow oil which was crystallized in a freezer overnight. Yield=65.4%.


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