GENERAL METHOD: A methanol (MeOH, 150 mL) solution of potassium hydroxide (KOH, 5.87 g, 104.65 mmol) was added to dimethyl glutarate (13.15 g, 90 mmol) and the reaction mixture was stirred for 4 hours at room temperature. After completion of the reaction, the solvent was removed under reduced pressure and extracted by adding ether (Et2O, 100 mL) and water (H2O, 200 mL). The organic layer was separated, washed with saturated brine, dried over anhydrous magnesium sulfate (MgSO4) and concentrated under reduced pressure to give compound 3a as a yellow oil (4.61 g, 32% yield). The aqueous layer was acidified to pH 3 with concentrated hydrochloric acid and subsequently extracted with ether (3 x 100 mL). The organic phases were combined, washed with saturated brine (3 x 100 mL) and dried over anhydrous magnesium sulfate (MgSO4). The solvent was removed under reduced pressure to give a mixture of white solid and oil. After filtration and vacuum concentration, the compound was purified by silica gel column chromatography to give compound 4a as a colorless oil (5.79 g, 44% yield).
