Hydrochloric Acid → (+/-)-3-(6-Methyl-2-p-tolyl-imidazo[1,2-alpha]pyridin-3-yl)-piperidin-2-one

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To a magnetically stirred solution of (+/−)-5-(2-methyl-propane-2-sulfinylamino)-2-(6-methyl-2-p-tolyl-imidazo[1,2-a]pyridin-3-yl)-pentanoic acid methyl ester 44b (0.039 g, 0.0824 mmol) in methanol (3 mL) at room temperature under Ar atmosphere was 5N HCl (1.71 mL). The reaction mixture was stirred for 3 h at room temperature, then concentrated in vacuo. The reaction mixture was treated with 10% aq NaOH solution until basic. After 30 mm, water (30 mL) was added, and the aqueous phase was extracted with EtOAc (2×50 mL). The combined organic layers were dried (MgSO4), and concentrated in vacuo to the crude product. The pure product was obtained by column chromatography over silica gel (EtOAc, then 4:96 MeOH/EtOAc as eluent) which gave the title compound (0.0202 g, 77%) as a white solid. 1H NMR (400 MHz, CDCl3) δ 1.92 (m, 1H), 2.04 (m, 2H), 2.16 (m, 1H), 2.32 (s, 3H), 2.39 (s, 3H), 3.50 (m, 2H), 4.28 (dd, J=6.2, 12.4 Hz, 1H), 6.37 (s, 1H), 7.00 (d, J=10.2 Hz, 1H), 7.24 (d, J=8.0 Hz, 2H), 7.56 (m, 3H). Mass spectrum (m/e) 320 (M+).

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