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A mixture of 20 g of dibutylketone, 19.3 g of salicylamide and 2.7 g of p-toluenesulfonic acid monohydrate is added to 300 ml of toluene and the mixture is refluxed overnight by making use of a dehydrator of Dean Stark. After cooling, the reaction mixture is washed, dried and evaporated to remove the solvent. The residue is purified by silica gel column chromatography (solvent; hexane:ethyl acetate=95:5) to obtain 34 g of 2,2-dibutyl-4-oxo-2,3-dihydro-4H-1,3-benzoxazine as a yellow oil.

1. temperaturethe mixture is refluxed overnight
2. temperatureAfter cooling
3. washthe reaction mixture is washed
4. customdried
5. customevaporated
6. customto remove the solvent
7. customThe residue is purified by silica gel column chromatography (solvent; hexane:ethyl acetate=95:5)