One-Step Synthesis of 4H-3,1-Benzoxazin-4-ones from Weinreb Amides and 1,4,2-Dioxazol-5-ones via Cobalt-Catalyzed C–H Bond Activation

General.Infrared (IR) spectra were recorded on a JASCO FT/IR4100 spectrophotometer and absorbance bands are reported in wave numbers (cm -1 ). 1 H and 13 C NMR spectra were recorded on JEOL JNM-ECX400P spectrometer, JEOL JNM-ECS400 spectrometer, or JEOL JNM-ECA500 spectrometer.Chemical shifts were reported in the scale relative to TMS (0.00 ppm for 1 H NMR), CHCl3 (7.26 ppm for 1 H NMR), CDCl3 (77.0 ppm for 13 C NMR), C6H5D (7.16 ppm for 1 H NMR), and C6D6 (128.0 ppm for 13 C NMR), respectively.ESI-MS spectra were obtained on JEOL JMS-T100LC AccuTOF.Silica gel column chromatography was performed with Kanto Silica gel 60 N (40-50 mesh).1,2-Dichloroethane (Wako Ltd., deoxidized grade) was stored over activated molecular sieves 3A or 4A under argon atmosphere before use.Cp*Co(CO)I2 was synthesized according to the literature. 1 Acetic anhydride was distilled before use.All Weinreb amide derivatives 2, O-methyl hydroxamate 5 and morpholine amide 6 were prepared from corresponding carboxylic acid or acyl chloride and N,O-dimethylhydroxylamine hydrochloride.All dioxazolone derivatives were synthesized according to the literature. 2 All other reagents were commercially available and used as received.General procedure of Cp*Co III -catalyzed one-step synthesis of benzoxazinone (for liquid substrate: 2a-2d, 2g-2l): To a dried screw-capped vial equipped with a stirring bar were added Cp*Co(CO)I2 (14.3 mg, 0.030 mmol, 10 mol %), AgSbF6 (20.6 mg, 0.060 mmol, 20 mol %), and 3 (97.9mg, 0.60 mmol, 2.0 equiv.)under argon atmosphere in a glovebox.The vial was charged with DCE (1.0 mL) followed by Ac2O (28.4 L, 0.30 mmol) and 2 (0.30 mmol).The mixture was stirred at room temperature for 15 min in the glovebox.The vial was capped, taken out of the glovebox, and the mixture was heated at 80 °C for 18 h with stirring.After the mixture was cooled to room temperature and diluted with CH2Cl2, saturated aqueous EDTA•2Na was added.The mixture was extracted with CH2Cl2 two times, and the combined S1 organic layers were dried over Na2SO4.After filtration and evaporation, the obtained crude mixture was purified by silica gel column chromatography (toluene/hexane/EtOAc = 60/10/1) to afford 1.General procedure of Cp*Co III -catalyzed one-step synthesis of benzoxazinone (for solid substrate: 2e, 2f): To a dried screw-capped vial equipped with a stirring bar were added Cp*Co(CO)I2 (14.3 mg, 0.030 mmol, 10 mol %), AgSbF6 (20.6 mg, 0.060 mmol, 20 mol %), 3 (97.9mg, 0.60 mmol, 2.0 equiv.), and 2 (0.30 mmol) under argon atmosphere in a glovebox.After the addition of DCE (1.0 mL) and Ac2O (28.4 L, 0.30 mmol), the mixture was stirred at room temperature for 15 min in the glovebox.The vial was capped, taken out of the glovebox, and the mixture was heated at 80 °C for 18 h with stirring.After the mixture was cooled to room temperature and diluted with CH2Cl2, saturated aqueous EDTA•2Na was added.The mixture was extracted with CH2Cl2 two times, and the combined organic layers were dried over Na2SO4.After filtration and evaporation, the obtained crude mixture was purified by silica gel column chromatography (toluene/hexane/EtOAc = 60/10/1) to afford 1. 2-Phenyl-4H-benzo[d][1,3]oxazin-4-one (1aa): a colorless solid (84%); 1 H NMR (CDCl3, 400 MHz)  8.35-8.29 (m, 2H), 8.25 (dd, J = 7.7 Hz, 1.4 Hz, 1H), 7.87-7.81(m, 1H), 7.71 (d, J = 7.7 Hz, 1H), 7.62-7.49(m, 4H); 13 C NMR (CDCl3, 125 MHz)  159.5, 157.0, 146.9, 136.5, 132.5, 130.1, 128.7, 128.5, 128.2, 128.2, 127.2, 116.9.(Reported compound. 3 ) 7-Methoxy-2-phenyl-4H-benzo[d][1,3]oxazin-4-one (1ba): a colorless solid (83%); 1 H NMR (CDCl3, 400 MHz)  8.34-8.29 (m, 2H), 8.15 (d, J = 8.7 Hz, 1H), 7.61-7.56(m, 1H), 7.55-7.49(m, 2H), 7.11 (d, J = 2.6 Hz, 1H), 7.06 (dd, J = 8.7 Hz, 2.6 Hz, 1H), 3.97 (s, 3H); 13 C NMR (CDCl3, 125 MHz)  166.2, 159.1, 157.9, 149.3, 132.5, 130.2, 130.1, 128.7, 128.2, 117.3, 109.7,108.8, 55.8.(Reported compound. 4 ) 7-Fluoro-2-phenyl-4H-benzo[d][1,3]oxazin-4-one (1ca): a colorless solid (81%); 1 H NMR (CDCl3, 400 MHz)  8.34-8.29 (m, 2H), 8.27 (dd, J = 8.6 Hz, 5.9 Hz, 1H), 7. 63-7.58 (m, 1H), 7.56-7.50(m, 2H), 7.36 (dd, J = 9.3 Hz, 2.6 Hz, 1H), 7.23 (ddd, J = 9.1, 8.6 Hz, 2.6 Hz, 1H); 13 C NMR (CDCl3, 125 MHz) S2  167.7 (d, 1 JC-F = 258 Hz), 158.5, 158.3, 149.4 (d, 133.0, 131.3 (d, 129.8, 128.7, 128.4,116.6 (d,2 JC-F = 24.0Hz), 113.5 (d, 4 JC-F = 2.4 Hz), 113.2 (d, 2 JC-F = 22.8 Hz).(Reported compound. 3) 2-Phenyl-7-(trifluoromethyl)-4H-benzo[d][1,3]oxazin-4-one (1da): a colorless solid (56%); 1 H NMR (CDCl3, 400 MHz)  8.39-8.31(m, 3H), 8.00-7.98(m, 1H), 7.74 (dd, J = 8.2 Hz, 1.4 Hz, 1H), 7.66-7.60(m, 1H), 7.58-7.52(m, 2H); 13 C NMR (CDCl3, 125 MHz)  158.4, 158.3, 147.3, 137.9 (q, 2 JC-F = 33.6Hz), 136.5, 133.1, 129.6, 128.9, 128.5, 124.6 (q, 3 JC-F = 3.6 Hz), 124.3 (q, 3 JC-F = 3.6 Hz), 123.0 (q, 1 JC-F = 273 Hz), 119.5.(Reported compound. 3) 7-Acetyl-2-phenyl-4H-benzo[d][1,3]oxazin-4-one (1ea): a colorless solid (56%); IR (KBr) 3466, 1764, 1685, 1609, 1568, 1427 cm -1 ; 1 H NMR (CDCl3, 400 MHz)  8. 35-8.30(m, 3H), 8.24-8.21(m, 1H), 8.07-8.05(m, 1H), 7.65-7.58(m, 1H), 7.57-7.51(m, 2H), 2.73 (s, 3H); 13 C NMR (CDCl3, 100 MHz)  196.7, 158.7, 157.8, 147.2, 143.2, 133.0, 129.7, 129.0, 128.8, 128.4,127.3, 126.8, 119.9, 27.0; HRMS (ESI): m/z calculated for C16H12O3N + [M+H] + : 266.0812, found: 266.0813.Methyl 4-oxo-2-phenyl-4H-benzo[d][1,3]oxazine-7-carboxylate (1fa):