The general procedure for the synthesis of 4,4-dimethylpiperidine hydrochloride from 3,3-dimethylglutamine is as follows:
1. Preparation of 4,4-dimethylpiperidine: Under argon protection, solid lithium aluminum hydride (2.5 g, 64 mmol) was added to a 500 mL round-bottom flask, and 40 mL of anhydrous tetrahydrofuran was added slowly. The suspension was cooled to 0 °C and then a solution of 3,3-dimethylglutarimide (3.0 g, 21 mmol) dissolved in 20 mL of anhydrous tetrahydrofuran was slowly added. Gas was observed to escape during the reaction. After the addition was completed, the ice bath was removed and the reaction mixture was allowed to gradually warm up to room temperature. A condenser was installed and the flask was placed in an oil bath and heated to reflux for 3 hours.
2. Post-treatment: The reaction solution is cooled to room temperature and the flask is subsequently placed in a cold water bath. 2.5mL of water, 2.5mL of 15% aqueous sodium hydroxide solution and 7.5mL of water were added slowly and dropwise to produce a thick suspension. Add 150mL of dry ether, stir and filter to remove solids. Separate the organic layer, dry with anhydrous sodium sulfate and filter.
3. Salt formation: The organic solution was cooled in an ice bath and anhydrous hydrogen chloride gas was passed for 30 seconds to produce a thick white precipitate. The solid was collected by filtration to give 4,4-dimethylpiperidine hydrochloride (2.68 g, 85% yield). Mass spectrometry analysis (APCI+): m/z 114.1.
