Paper
Photochemical & Photobiological Sciences
cooled to 0 °C. To the cooled solution was added dropwise
sodium nitrite (7.24 mmol in 4.0 mL water) under stirring at
the same temperature and stirred for 10 min. Subsequently, a
2 2
solution of SnCl ·2H O (0.026 mol in 3.5 mL HCl (37%)) was
added dropwise. The resulting suspension was stirred at 0 °C
for 30 min. The precipitate was filtered, washed with diethyl
ether (2 × 10 mL) and dried under vacuum. The crude product
was used without further purification.
Fig. 1 Indole derivatives.
In this work, we set out to synthesise a family of indole 2.3. General method for the synthesis of compounds 3a–d
derivatives (Fig. 1). These were then to be screened in pre- and and 4a–d
post-emergent herbicide assays for the parameters photo-
synthesis, plant growth and germination inhibition.
23
According to a modified literature procedure, to a sus-
pension of substituted phenylhydrazine hydrochloride
(
1.25 mmol) and ketone (1.25 mmol) in water (3 mL) was
added H SO (0.7 mmol). The mixture was heated at 100 °C for
2
4
2
. Experimental
90 min. After the reaction was complete, the mixture was
cooled to 0 °C, and the precipitate was filtered off, washed
with water and dried under reduced pressure to provide the
crude product. Further purification was achieved by flash
column chromatography, eluting with hexane : ethyl acetate
2
.1 General
Unless otherwise noted, all commercially available reagents
were purchased from Aldrich Chemical Co. and used without
further purification. Column chromatography was performed
using Merck silica gel (230–400 mesh). Thin layer chromato-
graphy (TLC) was performed using Merck silica gel GF254 of
(
9 : 1) to yield the desired products.
.3.1. 2,3,4,9-Tetrahydro-1H-carbazole (3a). Yield: 45%.
24
2
25
Brown solid. Melting point: 122 °C, lit.: 118–120 °C. IR (KBr
0
.25 mm thickness. For visualization, TLC plates were devel-
−1
1
pellet, cm ): 3394, 3047, 2924, 2846, 1465, 1460, 740. H NMR
DMSO-d , 500 MHz) δ: 1.76–1.85 (m, 4H), 2.59–2.61 (m, 2H),
.67–2.69 (m, 2H), 6.87–6.91 (m, 1H), 6.94–6.97 (m, 1H), 7.21
d, J = 7.9 Hz, 1H), 7.30 (d, J = 7.6 Hz, 1H), 10.56 (s, 1H).
oped with either iodine vapor or acidic vanillin.
H Nuclear magnetic resonance ( H NMR) and C NMR
spectra were recorded on a Bruker Ascend™ 500 MHz instru-
(
2
(
6
1
1
13
ment. The coupling constants (J) are given in hertz (Hz) and 13
C NMR (DMSO-d
6
, 125 MHz) δ: 20.5, 22.7, 22.8, 22.9, 107.9,
10.4, 117.0, 117.8, 119.9, 127.2, 134.3, 135.5.
.3.2. 6-Chloro-2,3,4,9-tetrahydro-1H-carbazole (3b).
Yield: 62%. Pale yellow solid. Melting point: 162 °C, lit.:
chemical shifts are reported in parts per million (ppm), refer-
enced to the internal standard tetramethylsilane (TMS). The
abbreviations s, bs, d, t, q, m, and dd refer to singlet, broad
1
24
2
singlet, doublet, triplet, quartet, multiplet, and doublet of
1
25
−1
62–163 °C. IR (KBr pellet, cm ): 3402, 2939, 2846, 1465,
doublets, respectively. All NMR spectra were obtained with
CDCl or DMSO-d .
1
3
1435, 802. H NMR (CDCl , 500 MHz) δ: 1.83–1.93 (m, 4H),
3
6
2
8
.63–2.66 (m, 2H), 2.70–2.73 (m, 2H), 7.04 (dd, J = 1.9 Hz,
.5 Hz, 1H), 7.16 (d, J = 8.4 Hz, 1H), 7.40 (d, J = 1.9 Hz, 1H).
Fourier transform infrared spectroscopy (FTIR) analysis was
performed on a Shimadzu Iraffinity-1 spectrophotometer. KBr 13
C NMR (CDCl
3
, 125 MHz) δ: 20.7, 20.7, 23.05, 23.08, 23.2,
pellets were prepared by mixing the compounds (1 mg) with
pure and anhydrous KBr (100 mg). The qualitative analyses
were carried out using the following parameters: measured
1
10.0, 111.2, 117.3, 121.0, 124.7, 129.0, 133.9, 135.7.
26
2.3.3. 6-Bromo-2,3,4,9-tetrahydro-1H-carbazole (3c). Yield:
26
5
7%. Pale brown solid. Melting point: 158 °C, lit.: 152–154 °C.
mode (% transmittance), apodizaiton (Happ_Genzel), number
−1
IR (KBr pellet, cm ): 3402, 2931, 2908, 2839, 1573, 1465, 1435,
7
of scans (200), resolution (16), range (400–4000 cm− ) and
1
1
94. H NMR (DMSO-d , 500 MHz) δ: 1.74–1.84 (m, 4H),
6
gain (1). The spectra acquisition was done employing IRSolution
2
.56–2.58 (m, 2H), 2.67–2.69 (m, 2H), 7.06 (dd, J = 1.9 Hz,
software (version 1.50). The background obtained from KBr
8
.3 Hz, 1H), 7.18 (d, J = 8.3 Hz, 1H), 7.46 (d, J = 1.8 Hz, 1H),
pellets was automatically subtracted from the sample spectra.
1
13
0.85 (s, 1H). C NMR (DMSO-d , 125 MHz) δ: 20.3, 22.66,
Melting points were recorded on a PFM-II/MS Tecnopon
2
6
2.69, 22.7, 108.0, 110.5, 112.3, 119.3, 122.2, 129.1, 134.2, 136.3.
melting point apparatus.
27
2.3.4. 2,3,4,9-Tetrahydro-1H-carbazole-8-carboxylic acid (3d).
Compound 5 was purchased from Aldrich Chemical Co.
Yield: 71%. White solid. Melting point: 201–203 °C, lit.:
(CAS number: 120-72-9).
28
−1
2
1
5
01–203 °C. IR (KBr pellet, cm ): 3464, 3062, 2924, 2846,
Chl a fluorescence transients were measured using a
1
665, 1581, 1465, 1435, 1265, 748. H NMR (DMSO-d
00 MHz) δ: 1.77–1.82 (m, 4H), 2.61–2.64 (m, 2H), 2.74–2.76
6
,
Hansatech Handy-Plant Efficient Analyzer; a three LED array
allowed for illumination with 650 nm continuous light
(
(
(
m, 2H), 7.01 (t, J = 7.6 Hz, 1H), 7.59 (d, J = 7.6 Hz, 1H), 7.62
d, J = 7.3 Hz, 1H), 10.55 (s, 1H), 12.77 (s, 1H). C NMR
−
2 −1
(
gain 0.7, intensity 2830 μmol photons m
s
).
13
DMSO-d , 125 MHz) δ: 20.4, 22.71, 22.79, 22.87, 108.4, 112.5,
6
2
.2. General method for the synthesis of compounds 2a–d
1
17.5, 122.3, 122.6, 128.8, 134.7, 136.2, 168.1.
2
2
24
According to a modified literature procedure, a solution of
2.3.5. 2,3-Dimethyl-1H-indole (4a).
Yield: 34%. White
2
5
substituted phenyl amine (0.16 mol) in HCl (6.5 mL, 37%) was solid. Melting point: 112 °C, lit.: 104–106 °C. IR (KBr pellet,
Photochem. Photobiol. Sci.
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