To a stirred solution of 3-(4-amino-1-oxoisoindolin-2-yl)piperidine-2,6-dione (0.52 g, 2.0 mmol) in DMF (10 ml) was added pentanal (0.26 g, 3.0 mmol), acetic acid (0.24 g, 4.0 mmol), and sodium triactoxyborohydride (0.85 g, 4.0 mmol). The reaction mixture was stirred at room temperature for 6 hours. The solvent was evaporated in vacuo and the residue was dissolved in ethyl acetate (100 ml), washed with H2O (3×100 ml), brine (1×100 ml), and dried over MgSO4. The solvent was evaporated and the residue was partially purified by chromatography (ethyl acetate/hexane, 75:25) to give an off-white solid which was slurried in ethyl acetate and filtered to give 0.14 g (21%) of product as a white solid: mp 244–246° C.; 1H NMR (DMSO-d6) δ 11.00 (s, 1H), 7.28 (t, J=7.7 Hz, 1H), 6.92 (d, J=7.3 Hz, 1H), 6.73 (d, J=8.0 Hz, 1H), 5.54 (t, J=5.3 Hz, 1H), 5.12 (dd, J=5.1 and 13.2 Hz, 1H), 4.24 (d, J=17.2 Hz, 1H), 4.13 (d, J=17.2 Hz, 1H) 3.15–3.07 (m, 2H), 3.00–2.86 (m, 1H), 2.65–2.59 (m, 1H), 2.39–2.23 (m, 1H), 2.08–1.99 (m, 1H), 1.61–1.57 (m, 2H), 1.41–1.32 (m, 4H), 0.89 (t, J=6.8 Hz, 3H); 13C NMR (DMSO-d6) δ 172.83, 171.19, 168.86, 143.74, 132.00, 129.15, 126.42, 111.66, 109.86, 51.46, 45.69, 42.68, 31.20, 28.80, 28.21, 22.79, 21.96, 13.89; Anal. Calcd. For C18H23N3O3: C, 65.63; H, 7.04; N, 12.76. Found: C, 65.69; H, 7.22; N, 12.55.
