benzyl 2'-oxo-2',3'-dihydro-1'H-spiro[piperidine-4,4'-quinoline]-1-carboxylate → Spiro[piperidine-4,4'(1'H)-quinolin]-2'(3'H)-one

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The mixture of benzyl 2′-oxo-2′,3′-dihydro-1′H-spiro[piperidine-4,4′-quinoline]-1-carboxylate (1.2 g, 3.4 mmol) and Pd/C (200 mg) in MeOH (20 mL) was hydrogenated under atmosphere pressure at room temperature for 3 h. The catalyst was filtered and the filtrate was concentrated under reduced pressure. The residue was purified by preparative HPLC twice to give 1′H-spiro[piperidine-4,4′-quinolin]-2′(3′H)-one (110 mg, 11%) as a TFA salt. 1H NMR (CDCl3) δ 7.65 (d, J=7.5 Hz, 1H), 7.29-7.45 (m, 3H), 3.45 (d, J=12.3 Hz, 2H), 3.20 (t, J=12.3 Hz, 2H), 2.96 (s, 2H), 2.10-2.21 (m, 2H), 1.70 (d, J=14.1 Hz, 2H). MS (ESI) m/z 217.06 [M+H]+.

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