Example 2 Preparation of 3-(S)-tert-butoxycarbonylamino-4,5,6,7-tetrahydroacridoheptan-2-one (4): di-tert-butyl dicarbonate (25.5 g, 0.11 mol) was slowly added to a stirring solution of L-α-amino-ε-caprolactam (compound 3) (15 g, 0.11 mol) and potassium carbonate (26.7 g, 0.11 mol) in a solution of tetrahydrofuran (THF). Once the addition was complete, the reaction mixture was gradually warmed to room temperature and the reaction was continued with stirring for 18 hours. After completion of the reaction, the insoluble solids were removed by filtration and the filtrate was concentrated under reduced pressure to remove the solvent to afford 26.4 g (99% yield) of 3-N-Boc-aminoazepan-2-one (4) as a white solid. Thin layer chromatography (TLC) showed an Rf value of 0.91 (unfolding agent: hexane-ethyl acetate, 9:1). Mass spectrometry (electrospray) showed a molecular ion peak m/z 229 ([M+H]+). Nuclear magnetic resonance hydrogen spectrum (1H-NMR, CDCl3) δ: 1.39 (m, 2H), 1.50 (s, 9H), 1.82 (m, 2H), 2.03 (m, 2H), 3.25 (m, 2H), 4.29 (m, 1H), 5.91 (s, 1H), 6.36 (s, 1H).
