Sodium hydride → 2-(3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazin-4-yl)pyridine N-oxide

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To a suspension of 0.38 g sodium hydride (60% in paraffin composition) in 14 ml dimethylformamide, was added 1.00 g 3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazine, and 1.01 g 2-bromopyridine N-oxide hydrochloride was further added under ice-cooling, and the mixture was stirred for 16 hours at 70° C. The reaction mixture was poured to ice water, the resulting mixture was extracted with ethyl acetate, and the extract was washed with an aqueous solution of sodium chloride and dried over anhydrous magnesium sulfate. The solvent was distilled off from the dried solution under reduced pressure, the residue was subjected to column chromatography on silica gel, and elution was conducted by the use of a 3:1 mixture of chloroform and acetone, thus giving 0.34 g of 2-(3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazin-4-yl)pyridine N-oxide. Ethanolic solution of hydrogen chloride (a mixture of 1 ml concentrated hydrochloric acid and 5 ml ethanol) was then added to the product obtained above, the solvent was distilled off from the mixture, and the residue was recrystallized from acetone, thus giving 182 mg of 2-(3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazin-4-yl)pyridine N-oxide hydrochloride.

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