Bert, Giancarlo published the artcileThe nitration of 3-indolecarboxyaldehyde and ethyl 3-indoleglyoxylate, HPLC of Formula: 10242-03-2, the publication is Gazzetta Chimica Italiana (1961), 728-41, database is CAplus.
A suspension of 1 g. 3-indolecarboxaldehyde (I) in 8 ml. AcOH treated with 1.05 ml. HNO3 (d. 1.37), heated to 80° until an exothermic reaction began, and cooled rapidly gave 0.2 g. 6-nitro-3-indolecarboxaldehyde (II), m. 302-4° (Me2CO-EtOH). A solution of 5.7 g. KNO3 in 10 ml. H2SO4 was added slowly at 10° to 5 g. I in 15 ml. concentrated H2SO4, the mixture stirred 10 min., poured onto ice, and the precipitate extracted with 100 ml. boiling C6H6 to yield 5.5 g. mixture, which was shown by spectrophotometric analysis to consist of 34% II and 66% 5-nitro-3-indolecarboxaldehyde (III), m. 300-2°; fractional crystallization from EtOH allowed partial separation of the two compounds A solution of 0.35 g. II in 10 ml. EtOH and 1 ml. 2N NaOH was boiled 15 min. with 0.25 g. KBH4, cooled, acidified, and extracted with Et2O; the residue of the evaporation of the Et2O was extracted with ligroine to give 5 mg. yellow needles (6-nitroskatole ?), m. 122-4°; the ligroineinsol. part yielded after extraction with C6H6 25 mg. 3-hydroxymethyl-6-nitroindole (IV), m. 144-6° (decomposition). Oxidation of 0.2 g. II in 1 ml. 2N NaOH by refluxing 1 hr. with 0.54 g. AgNO3 in 10 ml. 2N NH3 gave 60 mg. 6-nitro-3-indolecarboxylic acid (V), m. 265-7°; the same result was obtained with alk. KMnO4; similarly the mixture of II and III gave a mixture, m. 225-30°, of V and 5-nitro-3-indolecarboxylic acid (VI). V and VI were transformed resp. into 6- and 5-nitroindole by heating at 160-80° in quinoline. A suspension of 1 g. ethyl 3-indoleglyoxylate (VII) in 8 ml. AcOH heated 30 min. at 80° with 0.8 ml. HNO3 (d. 1.37) gave 0.4 g. ethyl 6-nitro-3-indolecarboxylate (VIII), m. 284-6° (decomposition) (EtOH), while 0.11 g. 4-nitro-3-indoleglyoxylate, m. 184-6° (EtOH), was obtained by concentration of the mother liquor. Nitration of 4 g. VII in 28 ml. concentrated H2SO4 with 2.8 g. KNO3 led to 3.3 g. mixture of 34% VIII and 66% ethyl 5-nitro-3-indoleglyoxylate (IX), m. 280-2° (decomposition), which was separated in part by crystallization from Me2CO. Saponification of VIII with KOH in EtOH gave the free acid (X), decomposing above 250° (Me2NCHO-H2O); similarly, IX yielded 5-nitro-3-indolecarboxylic acid (XI), decomposing at 233° (Me2NCHO-H2O). X and XI were decarboxylated to II and III at 170-80° in quinoline. Ultraviolet curves were given for I, II, III, IV, VIII, and IX.
Gazzetta Chimica Italiana published new progress about 10242-03-2. 10242-03-2 belongs to indole-building-block, auxiliary class Indole,Nitro Compound,Carboxylic acid,Indole, name is 6-Nitro-1H-indole-3-carboxylic acid, and the molecular formula is C9H6N2O4, HPLC of Formula: 10242-03-2.
Referemce:
https://www.nature.com/articles/s41429-020-0333-2,
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