[C:1]1([CH:7]2[CH2:11][CH2:10][CH2:9][C:8]2=[O:12])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[C:13](=[O:18])=[N:14][C:15](Cl)=[O:16]>C(OCC)(=O)C.C(=O)(O)[O-].[Na+]>[C:1]1([CH:7]2[C:8]3[O:12][C:15](=[O:16])[NH:14][C:13](=[O:18])[C:9]=3[CH2:10][CH2:11]2)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1A solution of 2-phenylcyclopentanone (19.995 g, 125 mmol) and N-(chlorocarbonyl)isocyanate (23.70 g, 225 mmol) was stirred at 58° C. for 1 h and at 130° C. for 45 min. The resulting tarrified reaction mixture was dissolved in ethyl acetate and neutralized with saturated aqueous sodium bicarbonate solution. The organic layer was dried over anhydrous magnesium sulfate and filtered. The product was purified by column chromatography on silica gel to give 7-phenyl-6,7-dihydrocyclopenta[e][1,3]oxazine-2,4(3H,5H)-dione (3.751 g, 16.36 mmol, 13% yield) as brownish solid. LC-MS (M+H)+=230.0. 1H NMR (500 MHz, CDCl3) δ ppm 8.34 (1H, br s), 7.35 (2H, t, J=7.3 Hz), 7.27-7.32 (1H, m), 7.18 (2H, d, J=7.3 Hz), 4.20 (1H, t, J=7.6 Hz), 2.82-2.91 (1H, m), 2.61-2.79 (2H, m), 2.11-2.21 (1H, m).
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