S(=O)(=O)(O)O.[Cl:6][C:7]1[CH:8]=[CH:9][C:10]2[O:14][CH2:13][CH2:12][C:11]=2[CH:15]=1.[N+:16]([O-])([OH:18])=[O:17]>O>[Cl:6][C:7]1[CH:8]=[C:9]([N+:16]([O-:18])=[O:17])[C:10]2[O:14][CH2:13][CH2:12][C:11]=2[CH:15]=1To a stirred and cooled mixture of 32 ml of sulfuric acid and 14 ml of water there were added 17 g of 2,3-dihydro-5-chlorobenzofuran, while keeping the temperature at 25° C. After cooling to 0° C. there were added dropwise 14 ml of nitric acid. Stirring and cooling at 0° C. was continued for 44 hours. The reaction mixture was diluted with water (temp. <10° C.) and stirred for 15 min. The precipitate was filtered off, washed with water and recrystallized from a mixture of ethyl acetate and hexane (30:70), yielding 8.9 g (40.5%) of 5-chloro-2,3-dihydro-7-nitrobenzofuran (interm. 3).
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