Tetra-n-butylammonium tribromide → 2-Bromo-1-[8-(tert-butyl)-4-methyl-3,4-dihydro-2H-1,4-benzoxazin-6-yl]-1-ethanone

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Reaction Steps

A solution of the 1-[8-(tert-butyl)-4-methyl-3,4-dihydro-2H-1,4-benzoxazin-6-yl]-1-ethanone (2.61 g, 10.6 mmol) and tetra-n-butylammonium tribromide (6.62 g, 13.7 mmol) in acetic acid was stirred at room temperature for 3.5 hours under a nitrogen atmosphere, and then n-butylammonium tribromide (1.02 g, 2.12 mmol) was added and stirring was continued for 45 minutes. After distilling off the solvent under reduced pressure, ethyl acetate was added to the residue and the mixture was washed with saturated aqueous sodium hydrogencarbonate (twice) and brine in that order. It was then dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. The residue was subjected to silica gel chromatography (Wakogel-C200,80 g) and fractionated with hexane-toluene (1:3) to yield the title compound (977 mg, 28.4% yield) as bright golden yellow crystals.

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