[O:1]1[CH2:6][CH2:5][NH:4][C:3]2[CH:7]=[CH:8][CH:9]=[CH:10][C:2]1=2.[H-].[Na+].I[CH3:14]>O1CCCC1>[CH3:14][N:4]1[CH2:5][CH2:6][O:1][C:2]2[CH:10]=[CH:9][CH:8]=[CH:7][C:3]1=2Into a 250 mL 3-necked round bottom flask was placed a solution of 3,4-dihydro-2H-benzo[b][1,4]oxazine (4.8 g, 35.51 mmol) in tetrahydrofuran (50 mL). To the above was added NaH (2.3 g, 57.50 mmol) in several batches, while cooling to a temperature of 0-5° C. The mixture was stirred for 30 minutes at 0-5° C. To the above was added iodomethane (9.0 g, 63.41 mmol) dropwise with stirring, white cooling to a temperature of 0-5° C. The resulting solution was allowed to react, with stirring, overnight while the temperature was maintained at room temperature. The reaction progress was monitored by TLC (ethyl acetate/petroleum ether=1:2). A filtration was performed. The filtrate was concentrated by evaporation under vacuum using a rotary evaporator. The residue was purified by eluting through a column with a 1:100 ethyl acetate/petroleum ether solvent system. This resulted in 3.0 g (50%) of 4-methyl-3,4-dihydro-2H-benzo[b][1,4]oxazine as yellow oil.
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