6
X. CHEN AND X.-Y. ZHOU
In summary, K2CO3-catalyzed and acetonitrile-promoted decarboxylation of indole-3-
carboxylic acids are achieved, respectively, and the approaches allow for a wide range of 3-
carboxyl indoles with good to excellent yields. More applications of base-catalyzed decar-
boxylative functionalization of indole-2-carboxylic acids and indole-3-carboxylic acids are
under active investigation in our laboratory and will be disclosed in due course.
Experimental section
General methods
All commercially available reagents were used without further purification. Column
chromatography was performed on silica gel (200–300 mesh). The chemical shifts
1
(d) of the H NMR (600 MHz) signals are reported in ppm relative to tetramethylsi-
lane (TMS) and by employing the residual solvent resonance as the internal standard.
Data are reported in the following order: chemical shift, multiplicity [s (singlet), d
(doublet), dd (doublet of doublets), t (triplet), q (quartet), and m (multiplet)], coupling-
constants (Hz), and integration. The chemical shifts
(d) of the 13CNMR (151 MHz) signals are reported in ppm relative tetramethylsilane
(TMS) and by employing the solvent resonance as the internal standard.
Procedure A: A mixture of indole-3-carboxylic acid 1 (0.50 mmol) and K2CO3
(13.8 mg, 0.10 mmol, 20 mol%) in EtOH (3 mL) was added into a Schlenk flask (25 mL)
and stirred at 140 ꢁC. The reaction was monitored using thin layer chromatography
until the disappearance of starting material 1. Then, the solvent was evaporated under
reduced pressure and the residue was purified using column chromatography (petrol-
eum ether/ethyl acetate 20:1 to 10:1).
Procedure B: A mixture of indole-3-carboxylic acid 1 (0.50 mmol) in CH3CN (3 mL)
was added into a Schlenk flask (25 mL) and stirred at 140 ꢁC. The reaction was moni-
tored by thin layer chromatography until the disappearance of starting material 1. Then
the solvent was evaporated under reduced pressure and the residue was purified by col-
umn chromatography (petroleum ether/ethyl acetate 20:1 to 10:1).
1 H-indole (2a)
Yield A: > 99%, 59.0 mg; Yield B: > 99%, 59.0 mg. White solid, mp 50–52 ꢁC, Rf 0.51
(Hexane/EtOAc, 10:1). 1H NMR (600 MHz, CDCl3) d 8.08 (s, 1 H), 7.74 (d, J ¼ 7.9 Hz, 1 H),
7.43 (dd, J ¼ 8.1, 0.6 Hz, 1 H), 7.31–7.26 (m, 1 H), 7.24–7.19 (m, 2 H), 6.64 (t, J ¼ 2.1 Hz,
1 H); 13C NMR (151 MHz, CDCl3) d 135.8, 127.9, 124.2, 122.0, 120.8, 119.9, 111.1, 102.6.
1
Full experimental detail, H and 13C NMR spectra. This material can be found via
the “Supplementary Content” section of this article’s webpage.
Funding
The work was supported by the Natural Science Foundation of Guizhou Province [Grant No.
qiankehejichu [2018] number 1141], the Science and Technology Foundation Project of
Liupanshui [Grant No. 52020-2018-04-10] and National Natural Science Foundation of China
[No. 21763017].