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Stage #1: ethyl 1-(aminomethyl)cyclobutanecarboxylate hydrochloride With triethylamine In methanol at 20℃; for 0.5h;
Stage #2: 1-benzyloxycarbonyl-4-(tert-butyloxycarbonyl)piperazine-2-carboxaldehyde In methanol at 20℃; for 1h; Inert atmosphere;
Stage #3: With sodium cyanoborohydride at 0 - 20℃; for 2h;