Majima, Riko published the artcileSynthetic experiments in the indole group. VII. Nitration and bromination of β-indolecarboxylic ester and a new synthesis of the dye of the purple of antiquity, Computed Properties of 10242-03-2, the publication is Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen (1930), 2237-45, database is CAplus.
cf. C. A. 20, 758. A repetition of the work of Oddo and Sessa (C. A. 5, 2638) not only confirmed the earlier observation that, contrary to the statements of O. and S., Et β-indolecarboxylate (I) is formed by the action of ClCO2Et on indolylmagnesium iodide but also showed that di-Et N, β-indoledicarboxylate (II) is formed at the same time; to obtain II in good yield it is well to use 2 mols. ClCO2Et per mol. of indole. Addition of concentrated HNO3 to I in cold AcOH gives chiefly Et 6-nitroindole-3-carboxylate (III), saponified by KOH to the free and (IV) which with hot quinoline gives 6-nitroindole (V). The position of the NO2 group was established by oxidation of the salt of IV with aqueous KMnO4 to 2,4-H2N(O2N)C6H3-CO2H. With HCl and SnCl2 in AcOH III readily yields the 3-amino ester (VI). V similarly gives the amorphous and very unstable 6-aminoindole (VII). I is readily brominated in AcOH, giving chiefly either Et 6-bromoindole-3-carboxylate (VIII) or the 5,6-di-Br ester (IX), depending on the conditions. The free di-Br acid (X) can be further converted into 5,6-dibromoindole (XI). X with CrO3 in AcOH gives a red 5,6-dibromoisatin (XII), m. above 290°, which on distillation with KOH yields a Br2C6H3NH2, m. 79-80° (of the known Br2C6H3NH2, the 3,4-compound, m. 80.4°, comes closest in its properties to the one obtained from XII). XII on further oxidation with CrO3 in AcOH gives a dibromoisatoic acid (XIII) which with concentrated HCl yields 4,5,2-Br2(H2N)C6H2CO2H, m. 227-8°. In the same way VIII gave 6-bromoisatin (XIV), different from Borsche and Jacobs’ synthetic 5-Br compound With 03 in alk. solution, VIII readily gives 6,6′-dibromoindigo (XV), thus further confirming the structure of VIII. II (1.1 g. from 3 g. indole through the Mg compound with 2 mols. ClCO2Et), less soluble in alc. than I, m. 102-3°. The yield of I has been increased to over 78% by slowly adding 11 g. ClCO2Et to the Mg derivative from 11 g. indole in cold Et2O. III, light yellowish needles, m. 198-9°. IV, yellow, becomes opaque at 227°, decomposes around 275-8°; its alkali salts dissolve in H2O with orange-red color. V, yellow, m. 139-40.5°. VI, m. 149-50°; HCl salt; chloroplatinate. β-Indolealdehyde in AcOH with HNO3 (d. 1.4) gives an addition product, C9H7ON.HNO3, decomposes 94°; with excess of HNO3 on the H2O bath is obtained a nitro-β-indolealdehyde, light yellow, m. around 290° (decomposition), turns brownish in the air. VIII, m. 134-7°; free acid, m. 212°. IX (85% from 2 g. I and 4 g. Br), m. 223-5°. X, m. 255-7°; if, in the saponification of IX, the boiling with excess of ale. KOH is continued 10 hrs. the product is XI, m. 154°. XII, m. 290°, shows the indopbenin reaction, gives with dilute NaOH a dark violet precipitate which redissolves with yellow color on heating and acids reppt. the original XII. XIV, orange-red, m. 256-8°. 5,5′,6,6′-Tetrabrornoindigo, is obtained from IX with O3; it dyes silk in somewhat less reddish shades than XV, the chief constituent of the purple of the ancients.
Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen 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, Computed Properties of 10242-03-2.
Referemce:
https://www.nature.com/articles/s41429-020-0333-2,
Preparation of Indole Containing Building Blocks for the Regiospecific Construction of Indole Appended Pyrazoles and Pyrroles