Methyl iodide → 1,3-Cyclopentanedione, 2,2-dimethyl-

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Reaction Steps

A mixture of 2-methylcyclopentane-1,3-dione (49.98 g, 446 mmol), potassium hydroxide (25.5 g, 455 mmol) and iodomethane (30.1 mL, 481 mmol) in dioxane (390 mL) and water (130 mL) was heated to reflux for 5 h. A biphasic mixture of potassium hydroxide (10.4 g), iodomethane (12.5 mL), water (26 mL) and dioxane (78 mL) was added. The mixture was heated at reflux for 3 additional hours and then stirred at ambient temperature overnight. Another portion of a biphasic mixture of potassium hydroxide (10.4 g), iodomethane (12.5 mL), water (26 mL) and dioxane (78 mL) was added. The mixture was heated at reflux for 3 h, cooled to room temperature and extracted with ether (600 mL, then 2×400 mL). The combined extracts were concentrated using a rotavap while keeping the bath temperature at or below room temperature to prevent loss of volatile product. The residue was treated with 10% hydrochloric acid (250 mL) and placed in a 120° C. oil bath until it started to boil (˜15 min). The mixture was cooled with an ice-water bath, diluted with water (250 mL) and treated with careful addition of sodium carbonate until carbon dioxide release stopped. The pH of the solution was 8-9. The mixture was extracted with dichloromethane (4×200 mL). The combined extracts were dried (MgSO4), filtered and concentrated while keeping water bath at or below room temperature. The residue was further dried under vacuum briefly to remove residual solvent to give 2,2-dimethylcyclopentane-1,3-dione as tan solid (38.1 g, 68% yield). 1H NMR (400 MHz, chloroform-d) δ ppm 2.81 (4H, s), 1.16 (6H, s); LC retention time: 0.990 min (analytical HPLC Method F).

Provenance & Evidence