N-alkylation of 4-piperidone can be done in PTC conditions - and no need to isolate your piperidone as free base. Add to one liter of acetonitrile 3 mole finely powdered potassium carbonate, then add 10 g of PTC catalyst - TBAB or TEBA, or just polyethylene glycol-400. Stir this suspension 15 min at 50-60°C, and then add in little portions your 4-piperidone hydrochloride, watching that the CO2 evolution wasn't too vigorous. Stir another hour at 50-60°C, and then add dropwise phenethylbromide, and stir 15-20 h at mild reflux. Then cool, and filter off inorganic salts - if filtration goes too slowly, add to suspension some (30-40 ml) saturated sodium sulphate solution, this makes the sticky precipitate granular and filterable. Yield almost quantitative (trust me), and no distillation needed - as result you have slightly yellow solid with mp 60°C.
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