Synthesis
General procedure for the synthesis of 5-chloro-1H-indole-2-carboxaldehyde from (5-chloro-1H-indol-2-yl)methanol: (5-chloro-1H-indol-2-yl)methanol (1 eq.) was dissolved in tetrahydrofuran (THF, 0.5 M), manganese dioxide (3 eq.) was added, the reaction was stirred for 1.5 hr. at room temperature, and the progress of the reaction was monitored by thin layer chromatography (TLC) until the complete conversion of the feedstock. After completion of the reaction, the mixture was filtered through a diatomaceous earth pad, the filtrate was dried with anhydrous magnesium sulfate and concentrated under reduced pressure to remove the solvent to give the crude 5-chloro-1H-indole-2-carbaldehyde in 82% yield.
References
[1] Synlett, 2007, # 11, p. 1707 - 1710
[2] Chemical Communications, 2013, vol. 49, # 28, p. 2894 - 2896
[3] Patent: US2008/9485, 2008, A1. Location in patent: Page/Page column 41
[4] European Journal of Medicinal Chemistry, 2016, vol. 121, p. 561 - 577
[5] Bioorganic and Medicinal Chemistry, 2017, vol. 25, # 6, p. 1889 - 1900
