Synthesis
GENERAL PROCEDURE: Titanium tetrachloride (0.7 mL, 6 mmol) was slowly added to a stirred suspension of zinc powder (0.78 g, 12 mmol) in freshly distilled anhydrous tetrahydrofuran (15 mL) at room temperature and under a dry nitrogen atmosphere. After addition, the mixture was refluxed for 2 hours. After the formed suspension of low-valent titanium reagent was cooled to room temperature, a solution of 7-bromoindigo red (2 mmol) in tetrahydrofuran (10 mL) was added dropwise. The reaction mixture was stirred at room temperature for about 5 min under nitrogen protection. After confirming the completion of the reaction by thin layer chromatography (TLC) analysis, the reaction was quenched with 3% hydrochloric acid (15 mL) and subsequently extracted with chloroform (3 x 50 mL). The combined organic phases were washed with water (3 x 50 mL) and dried over anhydrous sodium sulfate. After concentration of the solvent under reduced pressure, the crude product was purified by column chromatography (petroleum ether/ethyl acetate = 5:1) to give pure 7-bromoindolone.
References
[1] Tetrahedron Letters, 2014, vol. 55, # 14, p. 2238 - 2242
[2] Tetrahedron Letters, 2000, vol. 41, # 47, p. 9089 - 9093
[3] Journal of Chemical Research, 2017, vol. 41, # 9, p. 537 - 540
[4] Patent: WO2017/199265, 2017, A1. Location in patent: Paragraph 000170
