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Example B19: Diisopropylamine (17 mL, 121 mmol) was dissolved in THF (50 mL) at 0 °C, n-butyllithium (2.5 M hexane solution, 48 mL, 120 mmol) was slowly added and the reaction was stirred for 10 minutes. Subsequently, cyclobutanecarboxylic acid (5.00 g, 49.9 mmol) was added and stirring was continued for 0.5 hours. Next, methyl iodide (9.00 g, 63.4 mmol) was added dropwise to the reaction mixture and the mixture was stirred at room temperature for 3 hours. After completion of the reaction, the mixture was concentrated to dryness. The residue was treated with saturated NaHCO3 solution and then extracted with DCM (2×). The organic phases were combined, washed with brine, dried over anhydrous Na2SO4 and concentrated to dryness to afford 1-methylcyclobutanecarboxylic acid (3.54 g, 62% yield) as a brown oil.