Diazomethane → 3-Oxo-cyclopentanecarboxylic acid methyl ester

To a solution of 2.8 g of 3-oxocyclopentanecarboxylic acid in 20 ml of diethyl ether was added ethereal solution of diazomethane under cooled with ice until the mixture turned pale yellow, and then the reaction mixture was concentrated under reduced pressure to give about 3.1 g of 3-oxocyclopentanecarboxylic acid methyl ester as crude product. Obtained methyl ester compound was dissolved in 20 ml of methanol and after the mixture was cooled to -50° C., 820 mg of sodium borohydride was added thereto at a time and the mixture was stirred for 20 minutes at the same temperature. After 1.3 ml of acetic acid was dropped slowly to the reaction mixture, methanol was removed under reduced pressure. To the residue was added 10 ml of water and the mixture was extracted with ethyl acetate and the extract was washed successively with water and a saturated aqueous solution of sodium chloride and dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give 3 g of the title compound as crude product having the following physical data.