[NH2:1][N:2]1[C:11]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[C:5]([OH:12])=[CH:4][C:3]1=[O:13].[C:14]1(=O)[CH2:17][CH2:16][CH2:15]1.C(O)(=O)C.C([BH3-])#N.[Na+]>CO>[CH:14]1([NH:1][N:2]2[C:11]3[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=3)[C:5]([OH:12])=[CH:4][C:3]2=[O:13])[CH2:17][CH2:16][CH2:15]1A solution of 1-amino-4-hydroxyquinolin-2(1H)-one (0.516 g, 2.9 mmol) and cyclobutanone (1.05 g, 15.0 mmol) in acetic acid (0.90 g, 15.0 mmol) and methanol (20 mL) was treated portion wise with sodium cyanoborohydride (0.94 g, 15.0 mmol), stirred for 48 hours and concentrated. The residue was treated with 0.5 M aqueous sodium bicarbonate, acidified to pH 2 with 1 M hydrochloric acid and extracted with ethyl acetate. The ethyl acetate was washed with brine, dried over sodium sulfate, filtered and concentrated, The crude material was chromatographed on silica gel eluting with 3:2 hexane/ethyl acetate to give 1-(cyclobutylamino)-4-hydroxyquinolin-2(1H)-one (0.400 g, 60%). MS (ESI+) m/z 231 (M+H)+. 1H NMR (300 MHz, DMSO-d6) δ 1.52 (m, 1H) 1.63 (m, 1H) 1.96 (m, 4H) 3.64 (m, 1H) 5.91 (s, 1H) 6.26 (d, J=6.62 Hz, 1H) 7.20 (t, J=8.09 Hz, 1H) 7.61 (m, 1H) 7.84 (m, 2H) 11.42 (s, 1H).
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