2-Amino-4-chlorophenol → ethyl 6-chloro-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylate

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반응 단계

43.0 g of 2-amino-4-chlorophenol was dissolved in 500 ml of anhydrous acetone containing 42.0 g of anhydrous potassium carbonate. That mixture was heated to reflux temperature and 23.0 g of ethyl 2,3-dibromopropionate was added dropwise. In three additional portions each, additional ester and carbonate were added to the refluxing mixture until a total of 124 g of carbonate and 85.8 g of ester had been added. The mixture was refluxed for 21 hours. Solids were filtered from the mixture and washed with acetone. The filtrate was stripped of solvent and the residue was taken up in water. The water solution was extracted with ether. The ether extract was dried (MgSO4) and the solvent was stripped. The residue was eluted through a silica gel column using Solvent No. 3, the solvent was stripped and the residue was recrystallized from ethanol, then from ether to give ethyl 6-chloro-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylate (3A), as white crystals, mp; 85.5°-86.5° C.

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