Methyl trans-3-(boc-amino)cyclobutanecarboxylate

Methyl /rara-3-amino-cyclobutanecarboxylate hydrochloride (39.94 g, 241 mmol) was suspended in dichloromethane (400 ml). The solution was cooled to 0°C before Et3N (4 equiv., 134 ml, 965 mmol) and Boc anhydride (1.2 equiv., 63.2 g, 289 mmol) were added. The cooling bath was removed and the mixture was stirred while slowly allowing to warm up to room temperature. After 20 hours of stirring, the salts were filtered off and the filtrate was rinsed three times with water. The organic layer was dried over sodium sulfate, filtered and concentrated in vacuo. The residue was triturated in heptane, the solid was filtered off and dried in air flow to give Methyl trans-3-(boc-amino)cyclobutanecarboxylate as a white solid.