Under stirring conditions, ethyl 5-hydrazino-3-methylpentanoate (4.44 g, 24 mmol) was dissolved in anhydrous tetrahydrofuran (25 mL), followed by the addition of triphenylphosphine (6.29 g, 24 mmol). The reaction mixture was heated to 40 °C and release of nitrogen gas was observed. After the gas release ceased, water (0.43 mL, 24 mmol) was added to the reaction system and stirring of the reaction mixture was continued for 18 hours. Upon completion of the reaction, a clarified solution was obtained by evaporation under reduced pressure at 40 °C and the remaining solid residue was suspended in a solvent mixture of ether (50 mL) and hexane (50 mL) and stirred for 2 hours. Triphenylphosphine oxide was removed by filtration and the filter cake was washed with ice-cold ether (5 x 10 mL). The filtrate and washings were combined and evaporated under reduced pressure at 45 °C. The resulting solid residue (3.91 g) was purified by silica gel column chromatography (100 g silica gel, eluent ethyl acetate-methanol mixed solvent, 9:1 v/v, Rf-value 0.22, using phosphomolybdic acid to develop the color) to yield the final product, 4-methylpiperidin-2-one, in pure form (2.52 g, 93% yield), as a non-hygroscopic, white solid, with melting point of 89-91 °C.
