Step 2: To a solution of ethyl 3-((tert-butoxycarbonyl)amino)cyclobutanecarboxylate (0.4 g, 1.64 mmol) in tetrahydrofuran (6.5 mL) was added a solution of lithium hydroxide monohydrate (0.138 g, 3.28 mmol) in water (6.5 mL), and the reaction mixture was stirred at room temperature overnight. After completion of the reaction, the reaction mixture was washed with ether (20 mL) and the aqueous phase was acidified with 1 M potassium bisulfate. The product was extracted with ethyl acetate (3×20 mL), the organic phase was dried with anhydrous magnesium sulfate, and concentrated under reduced pressure to give 3-(Boc-amino)cyclobutanecarboxylic acid (0.335 g, 95%) as a white crystalline solid: no molecular ion peaks were observed in the mass spectra.
