Stage 1: Synthesis of methyl 1-aminocyclobutanecarboxylate
Concentrated H2SO4 (10 ml) was slowly added to a methanol solution (30 ml) containing 1-(tert-butoxycarbonylamino)-cyclobutane-1-carboxylic acid (9.29 mmol, 1 eq.) at 0°C. The reaction mixture was refluxed at 0°C for 2 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was dissolved in distilled water and the pH was adjusted to 8-9 with saturated sodium bicarbonate solution, followed by extraction with ethyl acetate (2 x 200 ml). The combined organic phases were washed sequentially with distilled water (2 x 150 ml) and saturated NaCl solution (2 x 50 ml) and dried with anhydrous sodium sulfate. Finally, the solvent was removed by concentration under reduced pressure to afford methyl 1-aminocyclobutanecarboxylate as a white solid in 75% yield.
