Indoline-2-carboxylic acid was transformed into 6-nitroindoline-2-carboxylic acid, the methyl ester of which was easily dehydrogenated by DDQ to methyl 6-nitroindole--2-carboxylate (total yield: 67%). Methyl 5-nitroindole-2-carboxylate was obtained by the nitration of methyl 1-acetylindoline-2-carboxylate acid followed by dehydrogenation with MnO 2 in toluene in 40% total yield.

中文翻译：

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二氢吲哚-2-羧酸硝化合成5-和6​​-硝基吲哚-2-羧酸甲酯

二氢吲哚-2-羧酸转化为6-硝基二氢吲哚-2-羧酸，其甲酯很容易被DDQ脱氢生成6-硝基吲哚-2-羧酸甲酯（总收率：67%）。5-硝基吲哚-2-羧酸甲酯通过将1-乙酰基二氢吲哚-2-羧酸甲酯酸硝化，然后在甲苯中用MnO 2 脱氢得到，总产率为40%。