Methanol → 2-(7-amino-3,4-dihydro-2,2-dimethyl-2H-1,4-benzoxazin-4-yl)pyridine N-oxide

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Reaction Conditions

Reaction Steps

To a mixture of 8.05 g of 2-(3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazin-4-yl)pyridine N-oxide, 28.50 g of ammonium chloride, 140 ml of methanol and 140 ml of water was added 34.94 g of zinc dust with ice-cooling, and the mixture was stirred at 5° C. for 14 hours. The insolubles were filtered off, and the filtrate was concentrated and extracted with ethyl acetate. The organic layer was dried over anhydrous magnesium sulfate and the solvent was distilled off to give 7.32 g of crude 2-(7-amino-3,4-dihydro-2,2-dimethyl-2H-1,4-benzoxazin-4-yl)pyridine N-oxide. (2) In 30 ml of methylene chloride was dissolved 6.72 g of 2-(7-amino-3,4-dihydro-2,2-dimethyl-2H-1,4-benzoxazin-4-yl)pyridine N-oxide obtained in (1) above followed by addition of 2.6 ml of acetic anhydride with ice-cooling, and the mixture was stirred at room temperature for 4 hours. To the reaction mixture was added 20 ml of methanol to decompose excess acetic anhydride, and the solvent was distilled off to give 8-40 g of crude 2-(7-acetamido-3,4-dihydro-2,2-dimethyl-2H-1,4-benzoxazin-4-yl)pyridine N-oxide. (3) In 35 ml of acetic acid was dissolved 8.76 g of 2-(7-acetamido-3,4-dihydro-2,2-dimethyl-2H-1,4-benzoxazin-4-yl)pyridine N-oxide obtained in (2) above followed by dropwise addition of a solution of nitric acid in acetic acid (prepared from 1.49 ml of fuming nitric acid and 16 ml of acetic acid) with ice-cooling, and the mixture was stirred at room temperature for 1 hour. The reaction mixture was poured into ice-water and extracted with ethyl acetate. The organic layer was washed with water and dried over anhydrous magnesium sulfate, and the solvent was distilled off. The residue was subjected to silica gel column chromatography and elution was carried out with chloroform-acetone (1:1) to obtain crystals. Recrystallization from 40 ml of ethanol gave 5.10 g of 2-(7-acetamido-3,4-dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl)pyridine N-oxide.

Provenance & Evidence