Under nitrogen protection, ethylene dimethyl carbonate (6.3 g, 70 mmol) was dissolved in 1,4-dioxane (15 mL), sodium hydride (2.2 g, 55 mmol) was added, and the mixture was heated to reflux. Subsequently, a 1,4-dioxane (5 mL) solution of 4-methyl-2-pentanone (2.5 g, 25 mmol) was added slowly and dropwise to the suspension and the reaction was continued at reflux for 3 hours. Upon completion of the reaction, the mixture was poured into ice water, washed with hexane and subsequently neutralized with 1N hydrochloric acid and extracted with ether. The organic phases were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to afford the target product methyl 5-methyl-3-carbonylhexanoate (3.9 g, 98% yield) as an orange oil. The product was characterized by 1H-NMR (CDCl3): δ 0.94 (6H, d, J = 6.6 Hz), 2.10-2.25 (1H, m), 2.42 (2H, d, J = 7.0 Hz), 3.44 (2H, s), 3.74 (3H, s).
