Synthesis of 11H-indolo[3,2-c]quinolines by SnCl4-catalyzed cyclization of indole-3-carbaldehyde oximes

Article abstract of DOI:10.1007/s11172-019-2697-7

A new method for synthesizing 11H-indolo[3,2-c]quinolines by SnCl₄-catalyzed intramolecular electrophilic amination of 2-arylindole-3-carbaldehyde O-acetyl oximes was developed.

Full text of DOI:10.1007/s11172-019-2697-7

Russian Chemical Bulletin, International Edition, Vol. 68, No. 12, pp. 2262—2270, December, 2019
2262
Synthesis of 11H-indolo[3,2-c]quinolines by
SnCl4-catalyzed cyclization of indole-3-carbaldehyde oximes*
N. A. Aksenov,a A. Z. Gasanova,a F. Yu. Prokonov,a D. A. Aksenov,a G. M. Abakarov,b and A. V. Aksenova
aNorth Caucasus Federal University,
1A ul. Pushkina, 355017 Stavropol, Russian Federation.
E-mail: radioanimation@rambler.ru
bDagestan State Technical University,
70 prosp. Imam Shamil, 367010 Makhachkala, Russian Federation
A new method for synthesizing 11H-indolo[3,2-c]quinolines by SnCl4-catalyzed intra-
molecular electrophilic amination of 2-arylindole-3-carbaldehyde O-acetyl oximes was
developed.
Key words: indoloquinolines, alkaloids, amination, quinoline.
Quinoline is an important structural constituent of
derivatives of cinnamon aldehydes and 3-arylpropan-
ones 2.8—13 The synthesis can also be started from 2-aryl-
benzaldehyde oximes 3 to be converted to phenantri-
dines 4.14—19 This reaction could proceed under photo-
chemical,14—16 electrochemical,17 microwave,18 and
thermal activations19 (Scheme 1).
a number of natural and synthetic biologically active
substances, e.g., Mefloquine,1 quinine,2 and quini-
dine.3 Despite the fact that several name reactions are
suitable to construct this heterocyclic system (see, for
instance, Refs 4—7), considerable efforts are been made
to explore new synthetic methods tolerating a wide range
of substrates and expanding the structural variety of the
products.
Scheme 1
R = H, Ar, Ac, Alk, EtCOO; R´ = H, Alk
The results described above were used to develop an
interesting approach20,21 to indolo[2,3-c]quinolines 6
involving base-mediated intramolecular cyclization
of O-(2,4-dinitrophenyl)-3-arylindole-2-ketoximes 5
(Scheme 2). Deprotonation of indole increases the electron
density at the ortho position of 3-aryl substituent thus ac-
celerating the reaction. This is why the similar conditions
are unsuitable for the synthesis of indolo[3,2-c]quinolines.
The indoloquinoline alkaloids exhibit a wide range of
biological activities22—24 that attracts our attention to
Exploring such advantageous methods, we paid atten-
tion to the synthesis of quinolines 1 via intramolecular
cyclization of oximes of unsaturated carbonyl compounds.
The starting compounds in these reactions are often the
* Based on the materials of the 4th Russian Conference on
Medicinal Chemistry with International participation (June 9—14,
2019, Ekaterinburg, Russia).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2262—2270, December, 2019.
1066-5285/19/6812-2262 © 2019 Springer Science+Business Media, Inc.

11H-Indolo[3,2-c]quinolines
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
2263
Scheme 2
Scheme 3
Reagents and conditions: Lewis acid (3 equiv.), toluene, reflux,
7—12 h.
Table 1. Optimization of the reaction conditions for the synthe-
sis of compound 8a
Entry
Lewis acid
Solvent
t/h
Yield of 8a (%)
1
2
3
4
5
SnCl4
Fe(AcAc)3
ZnCl2
SnCl2•2H2O
TiCl4
Toluene
EtOH
18
10
10
12
17
46
15
15
R = H, Me, Cl, Br, OMe; R´ = OEt, NMe2
EtOH
a
Toluene
Toluene
—
b
—
heterocyclic systems of this type.25,26 We have recently
developed an efficient one-pot synthetic approach to
indolo[3,2-c]quinolines featuring the synthesis of indoles
from 2-aminoacetophenones and aryl hydrazines under
the Fischer conditions followed by treatment of the in-
termediate indoles with acylation reagents,27 nitroal-
kanes,28 and nitrostyrenes29 in polyphosphoric acid (PPA).
We also have recently reported the synthesis of in-
doloquinolines by the reaction of 2-nitroacetophenones
with aryl hydrazines followed by one-pot reduction and
acylation of the intermediate 2-(2-nitrophenyl)indoles
in PPA.30
We hypothesized that in the presence of Lewis acids
2-arylindole-3-carbaldehyde oximes will readily undergo
intramolecular electrophilic amination to give indolo-
[3,2-c]quinolines. Earlier,14—21 low reactivity of unsub-
stituted oximes in intramolecular amination has been
shown; therefore, the starting compounds of choice
for this research were 2-aryl-1H-indole-3-carbalde-
hyde O-acetyl oximes 7a—f. It should be underlined
that Rodríguez and co-workers31 have found that irradia-
tion of oxime 7a produces only 2-phenyl-1H-indole-3-
carbonitrile but not the desired cyclization products.
Therefore, we decided to study cyclization of oximes 7
under thermal activation conditions in the presence
of different Lewis acids. The reaction conditions
for the intramolecular cyclization of oximes 7 were opti-
mized using O-acetyl oxime 7a as a model compound
(Scheme 3, Table 1).
a No reaction occurs.
b Resinification.
synthetic scope of this reaction, 2-arylindoles 9a—f were
formylated32 to give the corresponding 2-arylindole-3-
carbaldehydes 10a—f. Aldehydes 10a—f were isolated pure
by crystallization and quantitatively converted into the
corresponding aldoximes 11a—f and then to O-acetyl
oximes 7a—f. Without additional purification, O-acetyl
oximes 7a—f were subjected to heterocyclization to afford
indolo[3,2-c]quinolines 8a—f in 25—49% yields. It is
of note that 2-β-naphthyl-1H-indole-3-carbaldehyde
O-acetyl oxime (7b) gives exclusively 12H-benzo[g]-
indolo[3,2-c]quinoline (8b) and no 13H-benzo[h]-
indolo[3,2-c]quinoline was detected (Scheme 4).
Under similar conditions 3-acetyl-3-arylindoles 14
undergo the Beckmann rearrangement to compounds 15
(Scheme 5). Intermediate oximes 13a,b and O-acetyl
oximes 14 derived from them were used in the next steps
without purification; the yields of 3-acetamino-2-arylin-
doles 15 were calculated based on the amounts of 3-acetyl-
2-arylindoles 12 used.
In summary, we elaborated the synthetic approach
to 11H-indolo[3,2-c]quinolines involving electrophilic
amination of 2-arylindole-3-carbaldehyde O-acetyl oximes.
The developed procedure opens up the prospects for the
construction of the hardly accessible indolo[3,2-c]quino-
lines including 12H-benzo[g]indolo[3,2-c]quinoline. The
synthesized compounds can be transformed into the
isocryptoleptine derivatives by treatment with iodometh-
ane following the standard procedure.33
The highest yield of the target product 8a was achieved
by refluxing oxime 7a in toluene in the presence of tin
tetrachloride for 7 h. As expected, O-unsubstituted oximes
were unreactive under these conditions. To evaluate the

2264 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
Aksenov et al.
Scheme 4
7—11: R = R´ = H (a), R + R´ = —CH=CH—CH=CH— (b), R = OMe, R´ = H (c), R = Cl, R´ = H (d), R + R´ = —OCH2CH2O— (e), R = Me,
R´ = H (f)
Reagents and conditions: i. POCl3, DMF, 30 min; ii. NH2OH (3 equiv.), Et3N (3 equiv.), EtOH, reflux, 2 h, then 20 °C, 2 h;
iii. AcCl (1.3 equiv.), pyridine, 20 °C, 2 h; iv. SnCl4 (3 equiv.), toluene, reflux, 7—12 h.
Scheme 5
7, 12—15: R = R´ = H (a), R + R´ = —CH=CH—CH=CH— (b)
Reagents and conditions: i. SnCl4, CH2Cl2, 0 °C, 30 min, then Ac2O, nitromethane, 20 °C, 3 h; ii. NH2OH (3 equiv.), Et3N (3 equiv.),
EtOH, reflux, 2 h, then 20 °C, 2 h; iii. AcCl (1.3 equiv.), pyridine, 20 °C, 2 h; iv. SnCl4, toluene.

11H-Indolo[3,2-c]quinolines
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
2265
2-(4-Methoxyphenyl)-1H-indole-3-carbaldehyde (10c). White
substance, yield 221 mg (88%), m.p. 208—210 °C (ethanol)
Experimental
1
(cf. Ref. 33: m.p. 207—209 °C). H NMR (DMSO-d6), δ: 3.86
Lewis acids (SnCl4 (98%), Fe(AcAc)3 (99%), TiCl4 (99%),
SnCl2•2H2O (98%), and ZnCl2 (97%)), POCl3, 2- phenylindole,
and nitromethane were purchased from Alfa Aesar. Commercially
available 2-(2-naphthyl)indole, 2-(4-methoxyphenyl)-1H-in-
dole, 2-(4-chlorophenyl)indole, and 2-(4-methylphenyl)-1H-
indole were purchased from abcr. Gute Chimie (Germany).
2-(2,3-Dihydro[b][1,4]dioxin-6-yl)-1H-indole was synthesized
as described earlier.34 Zinc chloride was calcined prior to use in
order to remove the water traces, other reagents were used as
received.
(s, 3 H, OMe); 7.16 (d, 2 H, H(3´), H(5´), J = 8.7 Hz); 7.20—7.30
(m, 2 H, H(5), H(6)); 7.48 (d, 1 H, H(7), J = 7.8 Hz); 7.73 (d,
2 H, H(2´), H(6´), J = 8.7 Hz); 8.19 (d, 1 H, H(4), J = 7.5 Hz);
9.95 (s, 1 H, CHO); 12.30 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 55.5 (OMe), 111.9 (C(7)), 113.1 (C(3)), 114.5 (2 C, C(3´),
C(5´)); 121.0 (C(5)), 122.1 (C(2)), 122.4 (C(6)), 123.5 (C(4)),
125.9 (C(4a)), 131.3 (2 C, C(2´), C(6´)); 135.9 (C(1´)), 149.3
(C(7a)), 160.6 (C(4´)), 185.5 (CHO). MS (ESI), m/z: 274.0840
[M + Na]+. C16H13NNaO2. Calculated: M = 274.0838. Rf 0.54
(EtOAc—hexane, 1 : 4).
1H and 13C NMR spectra were run on a Bruker AVANCE
III HD instrument (working frequencies of 400.13 (1H) and
100.61 MHz (13C)) in DMSO-d6. The chemical shifts are given
in the δ scale relative to the residual solvent signals. High resolu-
tion electrospray ionization mass spectrometry was performed
with a Bruker Maxis impact instrument using a direct inlet,
HCO2Na—HCO2H was used for calibration. IR spectra were
recorded with a Shimadzu IRAffinity-1S FTIR spectrophotom-
eter equipped with an attenuated total reflection attachment.
Purity of the compounds was monitored by TLC on the pre-
coated Silufol UV-254 plates with visualization under UV-light.
Melting points were measured with a Stuart SMP30 apparatus.
2-Arylindole-3-carbaldehydes 10a—f (general procedure).
Compounds 10a—f were synthesized by known procedure.35
A solution of 2-aryl-1H-indole 9a—f (0.01 mol) in a minimum
amount of DMF was added to the Vilsmeier—Haack reagent
(was prepared from phosphorus oxychloride (1 mL) and DMF
(3.15 mL)) maintaining the reaction temperature between 10 and
20 °C. The reaction mixture was heated at 45 °C for 30 min and
poured into a mixture of ice—water (100 mL) and 10% aqueous
NaOH (20 mL). The resulting mixture was refluxed for 1 h and
cooled to room temperature. The precipitate was collected by
filtration, washed with water, dried, and recrystallized.
2-Phenyl-1H-indole-3-carbaldehyde (10a). White substance,
yield 194 mg (88%), m.p. 236—240 °C (dioxane) (cf. Ref. 33:
m.p. 249—250 °C). 1H NMR (DMSO-d6), δ: 7.41—7.21 (m, 2 H,
H(5), H(6)); 7.52 (d, 1 H, H(7), J = 7.9 Hz); 7.67—7.56 (m, 3 H,
H(3´), H(4´), H(5´)); 7.85—7.76 (m, 2 H, H(2´), H(6´)); 8.23
(d, 1 H, H(4), J = 7.5 Hz); 9.98 (s, 1 H, CHO); 12.43 (s, 1 H,
NH). 13C NMR (DMSO-d6), δ: 112.5 (C(3)), 113.9 (C(7)),
121.5 (C(5)), 122.9 (C(6)), 124.2 (C(4)), 126.2 (C(2)), 129.5
(2 C, C(2´), C(6´)); 130.2 (C(3a)), 130.3 (C(4´)), 130.4 (2 C, C(3´),
C(5´)); 136.4 (C(1´)), 149.6 (C(7a)), 186.0 (CHO). MS (ESI), m/z:
244.0731 [M + Na]+. C15H11NNaO. Calculated: M = 244.0733.
2-(Naphthalen-2-yl)-1H-indole-3-carbaldehyde (10b). White
substance, yield 228 mg (84%), m.p. 242—244 °C (ethanol).
1H NMR (DMSO-d6), δ: 7.16—7.39 (m, 2 H, H(5), H(6)); 7.55
(d, 1 H, H(7), J = 7.8 Hz); 7.71—7.59 (m, 2 H, H(6´), H(7´));
7.91 (dd, 1 H, H(3´), J = 8.5 Hz, J = 1.7 Hz); 8.04 (dd, 1 H,
H(4´), J = 5.8 Hz, J = 3.6 Hz); 8.19—8.09 (m, 2 H, H(5´),
H(8´)); 8.26 (d, 1 H, H(6´), J = 7.3 Hz); 8.40 (s, 1 H, H(4));
10.09 (s, 1 H, CHO); 12.60 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 112.1 (C(7)), 113.8 (C(3)), 121.2 (C(4)), 122.6 (C(5)), 123.9
(C(6)), 125.9 (C(2)), 126.9 (C(6´)), 127.1 (C(7´)), 127.3
(C(8a´)), 127.5 (C(1´)), 127.8 (C(2´)), 128.6 (2 C, C(4´), C(5´));
129.8 (C(8´)), 132.7 (C(3a´)), 133.2 (C(2´)), 136.2 (C(4a´)),
149.0 (C(7a)), 185.9 (CHO). MS (ESI), m/z: 294.0884 [M + Na]+.
C19H13NNaO. Calculated: M = 294.0889. Rf 0.66 (EtOAc—
hexane, 1 : 1).
2-(4-Chlorophenyl)-1H-indole-3-carbaldehyde (10d). White
substance, yield 219 mg (86%), m.p. 262—264 °C (acetone)
(cf. Ref. 36: m.p. 263—265 °C). 1H NMR (DMSO-d6), δ: 7.15—7.38
(m, 2 H, H(5), H(6)); 7.52 (d, 1 H, H(7), J = 7.8 Hz); 7.66
(d, 2 H, H(3´), H(5´), J = 8.2 Hz); 7.81 (d, 2 H, H(2´), H(6´),
J = 8.2 Hz); 8.22 (d, 1 H, H(4), J = 7.6 Hz); 9.97 (s, 1 H, CHO);
12.50 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 112.1 (C(7)),
113.7 (C(3)), 121.1 (C(5)), 122.6 (C(4)), 123.9 (C(6)), 125.8
(C(2)), 128.7 (C(3a)), 129.1 (2 C, C(2´), C(6´)); 131.6 (2 C,
C(3´), C(5´)); 134.8 (C(1´)), 136.0 (C(4´)), 147.5 (C(7a)), 185.5
(C=O). MS (ESI), m/z: 278.0349 [M + Na]+. C15H10C1NNaO.
Calculated: M = 278.0343. Rf 0.71 (EtOAc—hexane, 1 : 4).
2-(2,3-Dihydro[b][1,4]dioxin-6-yl)-1H-indole-3-carbalde-
hyde (10e). White substance, yield 232 mg (83%), m.p. 251.3—
253.3 °C (DMF). 1H NMR (DMSO-d6), δ: 4.32 (d, 4 H,
OCH2CH2O, J = 13.6 Hz); 7.07 (d, 1 H, H(5´), J = 8.3 Hz);
7.32—7.17 (m, 4 H, H(5), H(6), H(7´), H(8´)); 7.47 (d, 1 H,
H(7), J = 7.8 Hz); 8.17 (d, 1 H, H(4), J = 7.4 Hz); 9.95 (s, 1 H,
CHO); 12.27 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 64.2
(OCH2CH2O), 64.4 (OCH2CH2O), 111.9 (C(7)), 113.2 (C(3)),
117.7 (C(5´)), 118.3 (C(8´)), 121.0 (C(7´)), 122.4 (C(5)), 122.8
(C(2)), 123.2 (C(4)), 123.6 (C(6)), 125.9 (C(3a)), 135.8 (C(7´)),
143.7 (C(7a)), 145.1 (C(4a´)), 148.8 (C(8a´)), 185.4 (CHO).
MS (ESI), m/z: 302.0790 [M + Na]+. C17H13NNaO3. Calculated:
M = 302.0788. Rf 0.51 (EtOAc—hexane, 1 : 1).
2-(p-Tolyl)-1H-indole-3-carbaldehyde (10f). White substance,
yield 209 mg (89%), m.p. 232—235 °C (ethanol) (cf. Ref. 33:
m.p. 239—241 °C). 1H NMR (DMSO-d6), δ: 2.41 (s, 3 H, Me);
7.19—7.31 (m, 2 H, H(5), H(6)); 7.41 (d, 2 H, H(3´), H(5´),
J = 7.9 Hz); 7.50 (d, 1 H, H(7), J = 7.8 Hz); 7.67 (d, 2 H, H(2´),
H(6´), J = 7.9 Hz); 8.20 (d, 1 H, H(4), J = 7.5 Hz); 9.96 (s, 1 H,
CHO); 12.39 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 21.0 (Me),
112.0 (C(7)), 113.3 (C(3)), 121.0 (C(5)), 122.4 (C(4)), 123.7
(C(6)), 125.9 (C(3)), 127.0 (C(3a)), 129.6 (2 C, C(2´), C(6´));
129.8 (2 C, C(3´), C(5´)), 135.9 (C(4´)), 139.7 (C(1´)), 149.3
(C(7a)), 185.5 (CHO). MS (ESI), m/z: 258.0885 [M + Na]+.
C16H13NNaO. Calculated: M = 258.0889. Rf 0.65 (EtOAc—hex-
ane, 1 : 4).
3-Acetyl-2-arylindoles 12a,b (general procedure). Compounds
12a,b were synthesized by the earlier described procedure.37 To

2266 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
Aksenov et al.
a stirred solution of indole 9 (10.0 mmol) in CH2Cl2 (20 mL),
SnCl4 (1.44 mL, 12.0 mmol) was added in one portion at 0 °C.
Cooling was removed and the mixture was stirred at room tem-
perature for 30 min. To the resulting suspension, acetic anhydride
(2.1 mL, 10.0 mmol) and nitromethane (15 mL) were added by
small portions. After 3 h stirring at room temperature, the mix-
ture was treated with ice—water (30 mL), filtered to remove the
inorganic impurities, and extracted with ethyl acetate. The or-
ganic layer was dried with MgSO4 and concentrated in vacuo.
The products were purified by either recrystallization or column
chromatography (elution with EtOAc—petroleum ether, 1 : 4).
2-Acetyl-3-phenyl-1H-indole (12a). Colorless crystals, yield
1 g (43%), m.p. 232—235 °C (ethanol) (cf. Ref. 38: m.p. 171 °C).
1H NMR (DMSO-d6), δ: 2.07 (s, 3 H, Me); 7.27—7.17 (m, 2 H,
H(5), H(6)); 7.43 (d, 1 H, H(7), J = 7.3 Hz); 7.52—7.61 (m, 3 H,
H(3´), H(4´), H(5´)); 7.61—7.68 (m, 2 H, H(2´), H(6´)); 8.21
(d, 1 H, H(4), J = 7.4 Hz); 12.10 (s, 1 H, NH). 13C NMR
(DMSO-d6), δ: 30.1 (Me), 111.6 (C(7)), 114.3 (C(3)), 121.6
(C(5)), 121.8 (C(6)), 122.9 (C(4)), 127.0 (C(2)), 128.4 (2 C,
C(2´), C(6´)); 129.4 (C(4´)), 130.0 (2 C, C(3´), C(5´)); 132.7
(C(3a)), 135.4 (C(1´)), 144.9 (C(7a)), 193.6 (C=O). MS (ESI),
m/z: 258.0884 [M + Na]+. C16H13N1NaO. Calculated: M =
= 258.0889. Rf 0.31 (EtOAc—hexane, 1 : 4).
3-Acetyl-2-(naphthalen-2-yl)-1H-indole (12b). Colorless
crystals, yield 1.2 g (42%), m.p. 185.3—187.1 °C (EtOAc).
1H NMR (DMSO-d6), δ: 2.12 (s, 3 H, Me); 7.18—7.30 (m, 2 H,
H(5), H(6)); 7.46 (d, 1 H, H(7), J = 7.7 Hz); 7.59—7.69 (m, 2 H,
H(6´), H(7´)); 7.76 (dd, 1 H, H(3´), J = 8.5 Hz, J = 1.4 Hz);
8.13—8.00 (m, 3 H, H(4´), H(5´), H(8´)); 8.22 (d, 1 H, H(4),
J = 7.4 Hz); 8.24 (s, 1 H, H(1´)); 12.22 (s, 1 H, NH). 13C NMR
(DMSO-d6), δ: 30.3 (Me), 111.7 (C(7)), 114.5 (C(3)), 121.6
(C(5)), 121.9 (C(4)), 123.0 (C(6)), 126.9 (C(1´)), 127.1 (C(8a)),
127.2 (C(6´)), 127.6 (C(7´)), 127.8 (C(4´)), 127.9 (C(3´)), 128.3
(C(5´)), 129.4 (C(8´)), 130.1 (C(2)), 132.5 (C(3a)), 133.0
(C(2´)), 135.6 (C(4a´)), 144.8 (C(7a)), 193.7 (C=O). MS (ESI),
m/z: 308.1052 [M + Na]+. C20H15NNaO. Calculated: M =
= 308.1046. Rf 0.31 (EtOAc—hexane, 1 : 4).
2-Arylindole-3-carbaldehyde oximes 11a—f and 3-acetyl-2-
arylindole oximes 13a,b (general procedure). Compounds 11a—f
and 13a,b were synthesized by the earlier described modified
procedure.39 A 5-mL round bottom flask was charged with
2-aryl-1H-indole-3-carbaldehyde 10a—f or 12a,b (1 mmol),
hydroxylamine hydrochloride (0.207 g, 3 mmol), triethylamine
(0.3 mL, 3 mmol), and EOH (2 mL). The mixture was refluxed
for 1—2 h (TLC monitoring). After reaction completion, the
solvent was removed in vacuo, the residue was dissolved in ethyl
acetate (20 mL), and washed with water (3×15 mL). The com-
bined organic layers were dried and concentrated in vacuo. The
products were obtained in quantitative yields. Compounds
11a—f and 13a,b were used in the next step without purifica-
tion; if necessary, they can be purified by silica gel column
chromatography (gradient elution with ethyl acetate—hexane,
1 : 8→1 : 4).
2-Phenyl-1H-indole-3-carbaldehyde oxime (11a). White
substance, m.p. 179.2—183.1 °C. 1H NMR (DMSO-d6), δ: 7.13
(t, 1 H, H(5), J = 7.5 Hz); 7.21 (t, 1 H, H(6), J = 7.5 Hz); 7.43
(d, 1 H, H(7), J = 8.0 Hz); 7.48 (t, 1 H, H(4´), J = 6.9 Hz);
7.54—7.64 (m, 4 H, H(2´), H(3´), H(5´), H(6´)); 8.08 (d, 1 H,
H(4), J = 7.9 Hz); 8.26 (s, 1 H, CH=N); 10.72 (s, 1 H, NH);
11.76 (s, 1 H, OH). 13C NMR (DMSO-d6), δ: 105.8 (C(3)),
111.5 (C(7)), 120.5 (C(5)), 121.9 (C(6)), 122.8 (C(4)), 125.5
(C(2)), 128.6 (C(4´)), 129.0 (4 C, C(2´), C(3´), C(5´), C(6´));
131.3 (C(3a)), 136.0 (C(1´)), 139.7 (C(7a)), 144.3 (CH=N).
MS (ESI), m/z: 237.1026 [M + H]+. C15H13N2O. Calculated:
M = 237.1022. Rf 0.22 (EtOAc—hexane, 1 : 4).
2-(Naphthalen-2-yl)-1H-indole-3-carbaldehyde oxime (11b).
White substance, m.p. 182.8—187.2 °C. 1H NMR (DMSO-d6),
δ: 7.15 (ddd, 1 H, H(5), J = 7.9 Hz, J = 7.0 Hz, J = 0.8 Hz);
7.23 (ddd, 1 H, H(6), J = 8.1 Hz, J = 7.0 Hz, J = 1.1 Hz); 7.46
(d, 1 H, H(7), J = 8.0 Hz); 7.64—7.57 (m, 2 H, H(6´), H(7´));
7.75 (dd, 1 H, H(4´), J = 8.5 Hz, J = 1.7 Hz); 8.03—7.98 (m, 1 H,
H(3´)); 8.14—8.05 (m, 3 H, H(4), H(5´), H(8´)); 8.16 (s, 1 H,
H(1´)); 8.37 (s, 1 H, CH=N); 10.75 (s, 1 H, NH); 11.89 (s, 1 H,
OH). 13C NMR (DMSO-d6), δ: 106.3 (C(7)), 111.6 (C(3)), 120.6
(C(5)), 122.0 (C(4)), 122.9 (C(6)), 125.6 (C(2)), 126.6 (C(7´)),
126.9 (C(6´)), 126.9 (C(1´)), 127.8 (C(4´)), 128.1 (C(3´)), 128.3
(C(5´)), 128.5 (C(8´)), 128.9 (C(8a´)), 132.6 (C(3a)), 132.9
(C(2´)), 136.6 (C(4a´)), 139.6 (C(7a)), 144.4 (C=N). MS (ESI),
m/z: 387.1181 [M + H]+. C19H15N2O. Calculated: M = 387.1179.
Rf 0.23 (EtOAc—hexane, 1 : 4).
2-(4-Methoxyphenyl)-1H-indole-3-carbaldehyde oxime (11c).
White substance, m.p. 203.0—206 °C. 1H NMR (DMSO-d6), δ:
3.84 (s, 3 H, OMe); 7.15—7.08 (m, 3 H, H(5), H(3´), H(5´));
7.18 (ddd, 1 H, H(6), J = 8.2 Hz, J = 7.1 Hz, J = 1.2 Hz); 7.40
(d, 1 H, H(7), J = 8.0 Hz); 7.57—7.50 (m, 2 H, H(2´), H(6´));
8.05 (d, 1 H, H(4), J = 7.8 Hz); 8.24 (s, 1 H, CH=N); 10.65
(s, 1 H, NH); 11.65 (s, 1 H, OH). 13C NMR (DMSO-d6),
δ: 55.3 (OMe), 105.2 (C(3)), 111.4 (C(7)), 114.5 (2 C, C(3´),
C(5´)); 120.4 (C(5)), 121.7 (C(4)), 122.5 (C(6)), 123.7 (C(2)),
125.6 (C(1´)), 130.3 (2 C, C(2´), C(6´)), 136.2 (C(3a)), 139.8
(C(7a)), 144.5 (CH=N), 159.6 (C(4´)). MS (ESI), m/z: 267.1123
[M + H]+. C16H15N2O2. Calculated: M = 267.1128. Rf 0.28
(EtOAc—hexane, 1 : 4).
2-(4-Chlorophenyl)-1H-indole-3-carbaldehyde oxime (11d).
White substance, m.p. 239.5—256 °C. 1H NMR (DMSO-d6), δ:
7.13 (ddd, 1 H, H(5), J = 7.9 Hz, J = 7.0 Hz, J = 0.8 Hz); 7.22
(ddd, 1 H, H(6), J = 8.2 Hz, J = 7.0 Hz, J = 1.1 Hz); 7.43 (d, 1 H,
H(7), J = 8.0 Hz); 7.58—7.67 (m, 4 H, H(2´), H(3´), H(5´),
H(6´)); 8.08 (d, 1 H, H(4), J = 7.9 Hz); 8.25 (s, 1 H, CH=N);
10.78 (s, 1 H, NH); 11.81 (s, 1 H, OH). 1H NMR (DMSO-d6),
δ: 106.3 (C(3)), 111.6 (C(7)), 120.6 (C(5)), 122.0 (C(6)), 123.0
(C(4)), 125.5 (C(3)), 129.0 (2 C, C(2´), C(6´)); 130.2 (C(3a)),
130.6 (2 C, C(3´), C(5´)); 133.3 (C(1´)), 136.4 (C(4´)), 138.2
(C(7a)), 144.0 (CH=N). MS (ESI), m/z: 271.0635 [M + H]+.
C15H12ClN2O. Calculated: M = 271.0633. Rf 0.29 (EtOAc—hex-
ane, 1 : 4).
2-(2,3-Dihydrobenzo[b][1,4]dioxin-6-yl)-1H-indole-3-carb-
aldehyde oxime (11e). White substance, m.p. 157.0—165.1 °C
1
(DMF). H NMR (DMSO-d6), δ: 4.32 (s, 4 H, OCH2CH2O);
7.05—7.07 (m, 2 H, H(5), H(8´)); 7.08 (s, 1 H, H(5´)); 7.10—7.13
(m, 1 H, H(7´)); 7.18 (ddd, 1 H, H(6), J = 8.2 Hz, J = 7.1 Hz,
J = 1.2 Hz); 7.39 (d, 1 H, H(7), J = 8.0), 8.04 (d, 1 H, H(4),
J = 7.9); 8.24 (s, 1 H, CH=N); 10.67 (s, 1 H, NH); 11.63 (s, 1 H,
OH). 13C NMR (DMSO-d6), δ: 64.2 (OCH2CH2O), 64.3
(OCH2CH2O), 105.3 (C(3)), 111.4 (C(7)), 117.3 (C(5´)), 117.6
(C(8´)), 120.4 (C(7´)), 121.7 (C(5)), 122.1 (C(4)), 122.6 (C(6)),
124.4 (C(6´)), 125.6 (C(2)), 136.2 (C(3a)), 139.4 (C(7a)), 143.6
(C(8a´)), 144.0 (C(4a´)), 144.4 (CH=N). MS (ESI), m/z:
295.1078 [M + Na]+. C17H15N2O3. Calculated: M = 295.1077.
Rf 0.2 (EtOAc—hexane, 1 : 4).
2-(p-Tolyl)-1H-indole-3-carbaldehyde oxime (11f). White
substance, m.p. 203.3—205 °C. 1H NMR (DMSO-d6), δ: 2.39

11H-Indolo[3,2-c]quinolines
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
2267
(s, 3 H, Me); 7.12 (ddd, 1 H, H(5), J = 7.7 Hz, J = 7.2 Hz,
J = 0.7 Hz); 7.20 (ddd, 1 H, H(6), J = 8.0 Hz, J = 7.3 Hz,
J = 0.9 Hz); 7.37 (d, 2 H, H(3´), H(5´), J = 8.0 Hz); 7.42 (d, 1 H,
H(7), J = 8.0 Hz); 7.49 (d, 2 H, H(2´), H(6´), J = 8.0 Hz); 8.07
(d, 1 H, H(4), J = 7.9 Hz); 8.26 (s, 1 H, CH=N); 10.69 (s, 1 H,
NH); 11.70 (s, 1 H, OH). 13C NMR (DMSO-d6), δ: 20.9 (Me),
105.5 (C(3)), 111.5 (C(7)), 120.4 (C(5)), 121.8 (C(4)), 122.6
(C(6)), 125.6 (C(2)), 128.5 (C(3a)), 128.8 (2 C, C(2´), C(6´));
129.5 (2 C, C(3´), C(5´)); 136.3 (C(1´)), 138.2 (C(4´)), 139.8
(C(7a)), 144.4 (CH=N). MS (ESI), m/z: 251.1178 [M + H]+.
C16H15N2O. Calculated: M = 251.1179. Rf 0.34 (EtOAc—hexane,
1 : 4).
(C(5)), 122.1 (C(6)), 123.5 (C(4)), 125.2 (C(2)), 129.2 (2 C,
C(2´), C(6´)); 129.3 (2 C, C(3´), C(5´)); 129.4 (C(4´)), 130.4
(C(3a)), 136.4 (C(1´)), 144.1 (C(7a)), 151.7 (CH=N), 168.7
(C=O). MS (ESI), m/z: 301.0953 [M + Na]+. C17H14N2NaO2.
Calculated: M = 301.0947. Rf 0.29 (EtOAc—hexane, 1 : 4).
2-(Naphthalen-2-yl)-1H-indole-3-carbaldehyde O-acetyl
oxime (7b). White substance, m.p. 130.0—136.1 °C. 1H NMR
(DMSO-d6), δ: 2.20 (s, 3 H, Me); 7.25 (t, 1 H, H(5), J = 7.4 Hz);
7.31 (t, 1 H, H(6), J = 7.7 Hz); 7.53 (d, 1 H, H(7), J = 7.9 Hz);
7.67—7.60 (m, 3 H, H(4´), H(6´), H(7´)); 7.79 (dd, 1 H, H(3´),
J = 8.5 Hz, J = 1.6 Hz); 8.05—8.01 (m, 1 H, H(8´)); 8.15—8.08
(m, 2 H, H(1´), H(5´)); 8.18 (d, 1 H, H(4), J = 8.0 Hz); 8.66
(s, 1 H, CH=N); 12.33 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 19.7 (Me), 103.6 (C(3)), 111.9 (C(7)), 121.5 (C(5)), 122.2
(C(4)), 123.6 (C(6)), 125.3 (C(2)), 126.5 (C(6´)), 127.0 (C(7´)),
127.2 (C(1´)), 127.8 (C(4´)), 127.8 (C(3a)), 128.5 (C(3´)),
128.7 (C(5´)), 128.8 (C(8´)), 132.8 (C(8a´)), 132.9 (C(2´)),
136.6 (C(4a´)), 144.0 (C(7a)), 151.9 (CH=N), 168.8 (C=O). MS
(ESI), m/z: 351.1110 [M + Na]+. C21H16N2NaO2. Calculated:
M = 351.1104. Rf 0.22 (EtOAc—hexane, 1 : 4).
1-(2-Phenyl-1H-indol-3-yl)ethan-1-one oxime (13a). White
substance, m.p. 159.6—162.9 °C (cf. Ref. 40: m.p. 177—180 °C).
1H NMR (DMSO-d6), δ: 1.95 (s, 3 H, Me); 7.06 (t, 1 H, H(5),
J = 7.6 Hz); 7.15 (ddd, 1 H, H(6), J = 8.1 Hz, J = 6.9 Hz,
J = 0.9 Hz); 7.44—7.37 (m, 2 H, H(7), H(4´)); 7.53—7.47
(m, 2 H, H(3´), H(5´)); 7.61—7.57 (m, 2 H, H(2´), H(6´)); 7.73
(d, 1 H, H(4), J = 7.9 Hz); 10.89 (s, 1 H, NH); 11.56 (s, 1 H,
OH). 13C NMR (DMSO-d6), δ: 16.0 (Me), 110.7 (C(3)), 111.4
(C(7)), 119.8 (C(5)), 120.2 (C(4)), 122.0 (C(6)), 127.3 (C(2)),
128.1 (C(4´)), 128.5 (2 C, C(2´), C(6´)); 128.6 (2 C, C(3´),
C(5´)); 132.7 (C(3a)), 135.9 (C(1´)), 136.3 (C(7a)), 150.6
(C=N). MS (ESI), m/z: 251.1175 [M + H]+. C16H15N2O.
Calculated: M = 251.1179. Rf 0.22 (EtOAc—hexane, 1 : 4).
1-(2-(Naphthalen-2-yl)-1H-indol-3-yl)ethan-1-one oxime
(13b). White substance, m.p. 117.7—126.2 °C. 1H NMR
(DMSO-d6), δ: 1.99 (s, 3 H, Me); 7.11—7.02 (m, 1 H, H(5));
7.21—7.13 (m, 1 H, H(6)); 7.44 (d, 1 H, H(7), J = 7.5 Hz);
7.60—7.51 (m, 2 H, H(6´), H(7´)); 7.70 (d, 1 H, H(3´),
J = 8.0 Hz); 7.77 (d, 1 H, H(4´), J = 7.7 Hz); 8.08—7.91 (m, 3 H,
H(4), H(5´), H(8´)); 8.14 (s, 1 H, H(1´)); 10.92 (s, 1 H, NH);
11.70 (s, 1 H, OH). 13C NMR (DMSO-d6), δ: 16.1 (Me), 111.2
(C(3)), 111.4 (C(7)), 119.9 (C(5)), 120.3 (C(4)), 122.2 (C(6)),
126.58 (C(5´)), 126.61 (C(6´)), 126.8 (C(3´)), 127.2 (C(1´)), 127.4
(C(2´)), 127.7 (C(4´)), 128.0 (C(8´)), 128.1 (C(5´)), 130.2 (C(3a)),
132.4 (C(8a´)), 132.9 (C(4a´)), 136.1 (C(2´)), 136.3 (C(7a)),
150.7 (C=N). MS (ESI), m/z: 301.1339 [M + H]+. C20H17N2O.
Calculated: M = 301.1335. Rf 0.23 (EtOAc—hexane, 1 : 4).
2-Aryl-1H-indole-3-carbaldehyde O-acetyl oximes 7a—f and
3-acetyl-2-arylindole O-acetyl oximes 14a,b (general procedure).
Compounds 7a—f and 14a,b were synthesized as earlier de-
scribed.31 To a solution of oxime 11a—f or 13a,b (1 mmol) in
pyridine (1.2 mL), acetyl chloride (101 mg, 1.3 mmol) was
added dropwise and the mixture was stirred at room temperature
for 2 h. The mixture was diluted with ethyl acetate (50 mL) and
washed successively by 10% HCl (3×10 mL) and 5% aqueous
NaHCO3 (3×10 mL). The organic layer was dried with Na2SO4,
the drying agent was filtered off. Removal of the solvent in vacuo
afforded the title products in quantitative yields. Compounds
7a—f and 14a,b were used in the next step without purification;
if necessary, they can be purified by silica gel column chromato-
graphy (gradient elution with ethyl acetate—hexane, 1 : 8→1 : 4).
2-Phenyl-1H-indole-3-carbaldehyde O-acetyl oxime (7a).
White substance, m.p. 154.6—159.4 °C. 1H NMR (DMSO-d6),
δ: 2.19 (s, 3 H, Me); 7.23 (ddd, 1 H, H(6), J = 7.9 Hz, J = 7.2 Hz,
J = 0.9 Hz); 7.28 (ddd, 1 H, H(5), J = 8.1 Hz, J = 7.2 Hz,
J = 1.2 Hz); 7.49 (d, 1 H, H(7), J = 8.1 Hz); 7.68—7.52 (m, 5 H,
H(2´), H(3´), H(4´), H(5´), H(6´)); 8.14 (d, 1 H, H(4),
J = 7.9 Hz); 8.55 (s, 1 H, CH=N); 12.20 (s, 1 H, NH). 13C NMR
(DMSO-d6), δ: 19.7 (Me), 103.2 (C(3)), 111.9 (C(7)), 121.5
2-(4-Methoxyphenyl)-1H-indole-3-carbaldehyde O-acetyl
oxime (7c). White substance, m.p. 150.1—154 °C. 1H NMR
(DMSO-d6), δ: 2.19 (s, 3 H, Me); 3.85 (s, 3 H, OMe); 7.18—7.13
(m, 2 H, H(3´), H(5´)); 7.23—7.18 (m, 1 H, H(5)); 7.23—7.29
(m, 1 H, H(6)); 7.47 (d, 1 H, H(7), J = 7.8 Hz); 7.55—7.63
(m, 2 H, H(2´), H(6´)); 8.11 (d, 1 H, H(4), J = 7.6 Hz); 8.52
(s, 1 H, CH=N); 12.09 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 19.7 (Me), 55.4 (OMe), 102.5 (C(3)), 111.7 (C(7)), 114.6
(2 C, C(3´), C(5´)); 121.4 (C(5)), 121.9 (C(4)), 122.6 (C(2)),
123.2 (C(6)), 125.2 (C(3a)), 130.6 (2 C, C(2´), C(6´)); 136.3
(C(1´)), 144.3 (C(7a)), 151.9 (CH=N), 160.2 (C(4´)), 168.7
(C=O). MS (ESI), m/z: 331.1053 [M + Na]+. C18H16N2NaO3.
Calculated: M = 331.1053. Rf 0.12 (EtOAc—hexane, 1 : 4).
2-(4-Chlorophenyl)-1H-indole-3-carbaldehyde O-acetyl ox-
ime (7d). White substance, m.p. 195.7—205 °C. 1H NMR
(DMSO-d6), δ: 2.20 (s, 3 H, Me); 7.24 (ddd, 1 H, H(5),
J = 8.0 Hz, J = 7.1 Hz, J = 1.0 Hz); 7.30 (ddd, 1 H, H(6),
J = 7.9 Hz, J = 7.2 Hz, J = 1.2 Hz); 7.50 (d, 1 H, H(7),
J = 7.9 Hz); 7.67—7.70 (m, 4 H, H(2´), H(3´), H(5´), H(6´));
8.15 (d, 1 H, H(4), J = 7.7); 8.56 (s, 1 H, CH=N); 12.25 (s, 1 H,
NH). 13C NMR (DMSO-d6), δ: 19.7 (Me), 103.6 (C(3)), 112.0
(C(7)), 121.6 (C(5)), 122.2 (C(4)), 123.6 (C(6)), 125.1 (C(2)),
129.18 (2 C, C(2´), C(6´)); 129.2 (C(3a)), 131.0 (2 C, C(3´),
C(5´)); 134.2 (C(1´)), 136.5 (C(4´)), 142.6 (C(7a)), 151.6
(CH=N), 168.7 (C=O). MS (ESI), m/z: 335.0553 [M + Na]+.
C17H13Cl1N2NaO2. Calculated: M = 335.0558. Rf 0.33 (EtOAc—
hexane, 1 : 4).
2-(2,3-Dihydrobenzo[b][1,4]dioxin-6-yl)-1H-indole-3-carb-
aldehyde O-acetyl oxime (7e). White amorphous substance. 1H
NMR (DMSO-d6), δ: 2.19 (s, 3 H, Me); 4.33 (s, 4 H, OCH2-
CH2O); 7.07 (d, 1 H, H(8´), J = 8.3 Hz); 7.11 (d, 1 H, H(7´),
J = 8.4 Hz); 7.15 (d, 1 H, H(5´), J = 1.7 Hz); 7.20 (t, 1 H, H(5),
J = 7.4 Hz); 7.26 (t, 1 H, H(6), J = 7.2 Hz); 7.45 (d, 1 H, H(7),
J = 7.9 Hz); 8.10 (d, 1 H, H(4), J = 7.7 Hz); 8.53 (s, 1 H, CH=N);
12.07 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 19.7 (Me), 64.2
(OCH2CH2O), 64.3 (OCH2CH2O), 102.7 (C(3)), 111.8 (C(7)),
117.7 (C(5´)), 117.8 (C(8´)), 121.4 (C(5)), 122.0 (C(7´)), 122.4
(C(4)), 123.3 (C(6)), 123.4 (C(2)), 125.2 (C(6´)), 136.3 (C(3a)),
143.7 (C(7a)), 143.9 (C(8a´)), 144.6 (C(4a´)), 151.8 (CH=N),
168.7 (C=O). MS (ESI), m/z: 359.0996 [M + Na]+. C19H16N2NaO4.
Calculated: M = 359.1002. Rf 0.15 (EtOAc—hexane, 1 : 4).

2268 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
Aksenov et al.
2-(p-Tolyl)-1H-indole-3-carbaldehyde O-acetyl oxime (7f).
White substance, m.p. 165.1—168.8 °C. 1H NMR (DMSO-d6),
δ: 2.19 (s, 3 H, COMe); 2.40 (s, 3 H, Me); 7.24—7.19 (m, 1 H,
H(5)); 7.31—7.24 (m, 1 H, H(6)); 7.40 (d, 2 H, H(2´), H(6´),
J = 8.0 Hz); 7.48 (d, 1 H, H(7), J = 7.9 Hz); 7.54 (d, 2 H, H(3´),
H(5´), J = 8.1 Hz); 8.12 (d, 1 H, H(4), J = 7.7 Hz); 8.53 (s, 1 H,
CH=N); 12.14 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 19.7
(COMe), 20.9 (Me), 102.9 (C(3)), 111.8 (C(7)), 121.4 (C(5)),
122.0 (C(4)), 123.3 (C(6)), 125.2 (C(2)), 127.5 (C(3a)), 129.1
(2 C, C(2´), C(6´)); 129.7 (2 C, C(3´), C(5´)); 136.4 (C(1´)),
139.1 (C(4´)), 144.3 (C(7a)), 151.8 (CH=N), 168.7 (C=O). MS
(ESI), m/z: 315.1099 [M + Na]+. C18H16N2NaO2. Calculated:
M = 315.1104. Rf 0.37 (EtOAc—hexane, 1 : 4).
1-(2-Phenyl-1H-indol-3-yl)ethan-1-one O-acetyl oxime (14a).
White substance, m.p. 116.1—120.6 °C. 1H NMR (DMSO-d6),
δ: 2.05 (s, 3 H, Me); 2.21 (s, 3 H, COMe); 7.13 (ddd, 1 H, H(5),
J = 8.0 Hz, J = 6.9 Hz, J = 0.8 Hz); 7.21 (ddd, 1 H, H(6),
J = 7.9 Hz, J = 6.9 Hz, J = 0.8 Hz); 7.44 (d, 1 H, H(4),
J = 8.0 Hz); 7.47—7.56 (m, 3 H, H(3´), H(4´), H(5´)); 7.58—7.63
(m, 2 H, H(2´), H(6´)); 7.99 (d, 1 H, H(7), J = 7.9 Hz); 11.89
(s, 1 H, NH). 13C NMR (DMSO-d6), δ: 17.3 (CH3CO), 19.8
(CH3C=N), 107.9 (C(3)), 111.5 (C(7)), 120.6 (C(5)), 120.9
(C(6)), 122.6 (C(4)), 126.5 (C(2)), 128.7 (2 C, C(2´), C(6´));
128.8 (C(4´)), 129.1 (2 C, C(3´), C(5´)); 132.1 (C(3a)), 135.8
(C(1´)), 139.7 (C(7a)), 160.4 (C=N), 168.6 (C=O). MS (ESI),
m/z: 315.1109 [M + Na]+. C18H16N2NaO2. Calculated:
M = 315.1104. Rf 0.32 (EtOAc—hexane, 1 : 4).
1-(2-(Naphthalen-2-yl)-1H-indol-3-yl)ethan-1-one O-acetyl
oxime (14b). Yellow liquid. 1H NMR (DMSO-d6), δ: 1.80 (s, 3 H,
Me); 2.28 (s, 3 H, COMe); 7.21 (t, 1 H, H(5), J = 7.2 Hz); 7.30
(t, 1 H, H(6), J = 7.1 Hz); 7.45—7.59 (m, 4 H, H(7), H(4´),
H(6´), H(7´)); 7.64 (dd, 1 H, H(3´), J = 8.5 Hz, J = 1.5 Hz);
7.85—7.95 (m, 3 H, H(4), H(5´), H(8´)); 8.63 (s, 1 H, H(1´));
8.00 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 19.6 (CH3CO),
21.7 (CH3C=N), 108.3 (C(3)), 111.4 (C(7)), 120.7 (C(5)), 121.3
(C(4)), 123.3 (C(6)), 125.2 (C(6´)), 126.7 (C(7´)), 127.0 (C(2)),
127.1 (C(1´)), 127.2 (C(4´)), 128.0 (C(3´)), 128.4 (C(5´)), 129.2
(C(8´)), 129.4 (C(8a´)), 133.3 (C(3a)), 133.4 (C(4a´)), 135.9
(C(2´)), 136.8 (C(7a)), 160.7 (C(C=N)), 168.9 (C=O). MS
(ESI), m/z: 365.1269 [M + Na]+. C22H18N2NaO2. Calculated:
M = 365.1260. Rf 0.26 (EtOAc—hexane, 1 : 4).
11H-Indolo[3,2-c]quinolines 8a—f (general procedure). A 5-mL
round bottom flask was charged with 2-aryl-1H-indole-3-
carbaldehyde O-acetyl oxime 7a—f (1 mmol), toluene (1 mL),
and SnCl4 (0.354 mL, 3 mmol). The mixture was refluxed for
7—12 h (TLC monitoring). After the reaction completion, the
mixture was cooled, poured into water (20 mL), and acidified
with 20% aqueous ammonia (appr. 20 mL) to pH 9. The result-
ing solution was extracted with ethyl acetate (4×20 mL) and the
solvent was removed in vacuo. The products were purified
by silica gel column chromatography (gradient elution with
acetone—hexane, 1 : 4→1 : 1).
120.6 (C(7)), 121.9 (C(11b)), 122.1 (C(8)), 125.5 (C(2)), 125.7
(C(3)), 128.0 (C(1)), 129.5 (C(4)), 138.8 (C(10a)), 139.8
(C(11a)), 144.8 (C(6)), 145.4 (C(4a)). MS (ESI), m/z: 219.0911
[M + H]+. C15H11N2. Calculated: M = 219.0917. Rf 0.19 (ethyl
acetate). Rf 0.5 (hexane—acetone, 1 : 1).
12H-Benzo[g]indolo[3,2-c]quinoline (8b). White substance,
yield 94 mg (35%), m.p. 400 °C. IR (ATR), ν/cm–1: 3494, 2934,
1741, 1462, 1378, 1260, 1077, 1027. 1H NMR (DMSO-d6), δ:
7.37 (ddd, 1 H, H(9), J = 7.9 Hz, J = 7.1 Hz, J = 0.9 Hz); 7.50
(ddd, 1 H, H(10), J = 8.2 Hz, J = 7.2 Hz, J = 1.1 Hz); 7.67—7.58
(m, 2 H, H(2), H(3)); 7.76 (d, 1 H, H(11), J = 8.1 Hz); 8.27—8.15
(m, 2 H, H(1), H(4)); 8.33 (d, 1 H, H(8), J = 7.8 Hz); 8.79
(s, 1 H, H(13)); 9.12 (s, 1 H, H(5)); 9.67 (s, 1 H, H(7)); 13.02
(s, 1 H, NH). 13C NMR (DMSO-d6), δ: 112.1 (C(11)), 112.6
(C(7a), 117.5 (C(7b)), 119.9 (C(9)), 120.6 (C(8)), 120.9 (C(10)),
122.4 (C(12b)), 125.2 (C(2)), 126.0 (C(3)), 126.2 (C(1)),
127.4 (C(4)), 127.9 (C(13)), 128.5 (C(5)), 130.6 (C(12a)),
132.5 (C(13a)), 138.4 (C(4a)), 139.2 (C(5a)), 142.9 (C(11a)),
146.9 (C(7)). MS (ESI), m/z: 269.1077 [M + H]+. C19H13N2.
Calculated: M = 269.1073. Rf 0.26 (acetone—hexane, 1 : 2).
3-Methoxy-11H-indolo[3,2-c]quinoline (8c). White sub-
stance, yield 122 mg (49%), m.p. 303.1—307.8 °C. IR (ATR),
ν/cm–1: 3437, 2930, 1626, 1561, 1500, 1491, 1447, 1378, 1298,
1237, 1187, 1149, 1035. 1H NMR (DMSO-d6), δ: 3.94 (s, 3 H,
Me); 7.31 (ddd, 1 H, H(8), J = 7.9 Hz, J = 7.3 Hz, J = 0.7 Hz);
7.35 (dd, 1 H, H(2), J = 9.0 Hz, J = 2.6 Hz); 7.45 (ddd, 1 H,
H(9), J = 8.2 Hz, J = 7.1 Hz, J = 1.1 Hz), 7.55 (d, 1 H, H(4),
J = 2.5 Hz); 7.67 (d, 1 H, H(10), J = 8.1 Hz); 8.26 (d, 1 H, H(7),
J = 7.8 Hz); 8.42 (d, 1 H, H(1), J = 9.0 Hz); 9.52 (s, 1 H, H(6));
12.57 (s, 1 H, NH). 13C NMR (DMSO-d6), δ: 55.4 (Me), 109.0
(C(10)), 111.7 (C(6a)), 111.4 (C(4)), 113.4 (C(11b)), 117.4 (C(8)),
119.9 (C(7)), 120.5 (C(2)), 122.1 (C(6b)), 123.3 (C(9)), 125.2
(C(1)), 138.7 (C(11a)), 140.3 (C(10a)), 145.0 (C(6)), 147.3 (C(4a)),
159.3 (C(3)). MS (ESI), m/z: 249.1022 [M + H]+. C16H13N2O.
Calculated: M = 249.1022. Rf 0.17 (acetone—hexane, 1 : 1).
3-Chloro-11H-indolo[3,2-c]quinoline (8d). Colorless crystals,
yield 63 mg (25%), m.p. 310.1—313.7 °C (cf. Ref. 41: m.p.
310 °C). IR (ATR), ν/cm–1: 3441, 2930, 2850, 1744, 1626, 1565,
1508, 1454, 1344, 1226, 1138, 1073. 1H NMR (DMSO-d6), δ:
7.36 (t, 1 H, H(8), J = 7.5 Hz); 7.52 (t, 1 H, H(9), J = 7.5 Hz);
7.78—7.71 (m, 2 H, H(2), H(10)); 8.17 (d, 1 H, H(4), J = 1.7 Hz);
8.34 (d, 1 H, H(1), J = 7.8 Hz); 8.56 (d, 1 H, H(7), J = 8.8 Hz);
9.64 (s, 1 H, H(6)); 12.86 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 112.0 (C(10)), 114.7 (C(6a)), 115.8 (C(11b)), 120.3 (C(8)),
120.9 (C(7)), 121.7 (C(6b)), 124.2 (C(9)), 126.0 (C(1)), 126.2
(C(2)), 128.3 (C(4)), 132.5 (C(11a)), 138.9 (C(3)), 139.6
(C(10a)), 145.9 (C(4a)), 146.1 (C(6)). MS (ESI), m/z: 253.0525
[M + H]+. C15H10ClN2. Calculated: M = 253.0527. Rf 0.28
(EtOAc—hexane, 1 : 1). Rf 0.33 (acetone—hexane, 1 : 2).
2,3-Dihydro-12H-[1,4]dioxino[2,3-g]indolo[3,2-c]quinoline
(8e). White substance, yield 105 mg (38%), m.p. 390.0—393.3 °C.
IR (ATR), ν/cm–1: 2983, 1569, 1512, 1474, 1367, 1344, 1290,
1245, 1187, 1069. 1H NMR (DMSO-d6), δ: 4.41 (s, 4 H,
OCH2CH2O); 7.29 (t, 1 H, H(9), J = 7.5 Hz); 7.44 (ddd, 1 H,
H(10), J = 8.2 Hz, J = 7.1 Hz, J = 1.0 Hz); 7.51 (s, 1 H, H(13));
7.65 (d, 1 H, H(11), J = 8.1 Hz); 7.92 (s, 1 H, H(5)); 8.23 (d, 1 H,
H(8), J = 7.8 Hz); 9.37 (s, 1 H, H(7)); 12.41 (s, 1 H, NH).
13C NMR (DMSO-d6), δ: 64.2 (C(2)), 64.3 (C(3)), 107.0 (C(5)),
111.7 (C(13)), 112.2 (C(6a)), 113.1 (C(12b)), 114.6 (C(9)), 119.8
(C(8)), 120.4 (C(10)), 122.1 (C(6b)), 125.1 (C(7)), 138.5
(C(12a)), 139.4 (C(11a)), 141.8 (C(5a)), 143.2 (C(7)), 143.4
11H-Indolo[3,2-c]quinoline (8a). Colorless crystals, yield
100 mg (46%), m.p. 340—341 °C (cf. Ref. 30: m.p. 340—341 °C).
IR (ATR), ν/cm–1: 3047, 2775, 1571, 1519, 1462, 1373, 1341,
1242, 1158, 933, 771, 740. 1H NMR (DMSO-d6), δ: 7.34 (t, 1 H,
H(8), J = 7.3 Hz); 7.55—7.45 (m, 1 H, H(9)); 7.78—7.65 (m, 3 H,
H(2), H(3), H(10)); 8.14 (d, 1 H, H(7), J = 7.9 Hz); 8.32 (d, 1 H,
H(1), J = 7.8 Hz); 8.53 (dd, 1 H, H(4), J = 8.0 Hz, J = 1.1 Hz);
9.60 (s, 1 H, H(6)); 12.73 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 111.8 (C(10)), 114.3 (C(6a)), 117.1 (C(6b)), 120.1 (C(9)),

11H-Indolo[3,2-c]quinolines
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 12, December, 2019
2269
(C(13a)), 145.3 (C(4a)). MS (ESI), m/z: 277.0974 [M + H]+.
C17H13N2O2. Calculated: M = 277.0972. Rf 0.29 (EtOAc).
3-Methyl-11H-indolo[3,2-c]quinoline (8f). White substance,
References
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yield 100 mg (43%), m.p. 365.7—367.7 °C. IR (ATR), ν/cm–1
:
3429, 3044, 2934, 168, 1599, 1565, 1496, 1454, 1363, 1340, 1241,
1027. 1H NMR (DMSO-d6), δ: 2.56 (s, 3 H, Me); 7.32 (ddd,
1 H, H(8), J = 7.9 Hz, J = 7.1 Hz, J = 0.8 Hz); 7.47 (ddd, 1 H,
H(9), J = 8.2 Hz, J = 7.1 Hz, J = 1.1 Hz); 7.53 (dd, 1 H, H(2),
J = 8.3 Hz, J = 1.5 Hz); 7.69 (d, 1 H, H(11), J = 8.1 Hz); 7.93
(s, 1 H, H(4)); 8.28 (d, 1 H, H(7), J = 7.8 Hz); 8.41 (d, 1 H,
H(1), J = 8.3 Hz); 9.54 (s, 1 H, H(6)); 12.64 (s, 1 H, NH).
13C NMR (DMSO-d6), δ: 21.5 (Me), 111.8 (C(10)), 114.0
(C(11b)), 114.9 (C(6a)), 120.0 (C(8)), 120.6 (C(7)), 121.9 (C(9)),
122.0 (C(6b)), 125.4 (C(1)), 127.6 (C(2)), 128.8 (C(4)), 137.7
(C(11a)), 138.7 (C(10a)), 139.9 (C(4a)), 144.8 (C(6)), 145.7
(C(3)). MS (ESI), m/z: 233.1076 [M + H]+. C16H13N2. Calcul-
ated: M = 233.1073. Rf 0.18 (acetone—hexane, 1 : 2).
3-Acetamino-2-arylindoles 15a,b were synthesized from
3-acetyl-2-arylindole O-acetyl oximes 14a,b by the procedure de-
scribed above for the synthesis of 11H-indolo[3,2-c]quinolines 8.
Compounds 15a,b were isolated by silica gel column chromato-
graphy (gradient elution with ethyl acetate—hexane, 1 : 4→1 : 1).
N-(2-Phenyl-1H-indol-3-yl)acetamide (15a). White sub-
stance, yield 230 mg (92%), m.p. 206.1—207.7 °C (benzene)
(cf. Ref. 40: m.p. 199–203 °C). IR (ATR), ν/cm–1: 3433, 3265, 2918,
2861, 1664, 1588, 1542, 1477, 1443, 1393, 1371, 1275. 1H NMR
(DMSO-d6), δ: 2.10 (s, 3 H, Me); 7.00 (t, 1 H, H(5), J = 7.4 Hz);
7.13 (t, 1 H, H(6), J = 7.5 Hz); 7.32 (d, 1 H, H(4), J = 8.1 Hz);
7.37 (t, 2 H, H(3´), H(5´), J = 7.7 Hz); 7.46—7.52 (m, 2 H,
H(4), H(4´)); 7.78 (d, 2 H, H(2´), H(6´), J = 7.8 Hz); 9.44
(s, 1 H, NHCO); 11.38 (s, 1 H, NH). 13C NMR (DMSO-d6),
δ: 22.8 (Me), 110.8 (C(3a)), 111.4 (C(7)), 118.5 (C(5)), 119.0
(C(4)), 121.9 (C(6)), 126.2 (C(2)), 126.7 (2 C, C(2), C(6));
127.4 (C(4´)), 128.7 (2 C, C(3), C(5)); 131.3 (C(7a)), 131.7
(C(3)), 134.5 (C(1´)), 169.6 (C=O). MS (ESI), m/z: 273.1003
[M + Na]+. C16H14N2NaO. Calculated: M = 273.0998. Rf 0.17
(EtOAc—hexane, 1 : 1).
N-(2-(Naphthalen-2-yl)-1H-indol-3-yl)acetamide (15b). White
substance, yield 270 mg (90%), m.p. 189.8—191.1 °C (benzene).
IR (ATR), ν/cm–1: 3364, 3258, 3048, 2926, 1649, 1504, 1367,
1344, 1313, 1271, 1245, 1012. 1H NMR (DMSO-d6), δ: 2.16
(s, 3 H, Me); 7.04 (ddd, 1 H, H(5), J = 7.8 Hz, J = 6.9 Hz,
J = 0.7 Hz); 7.17 (ddd, 1 H, H(6), J = 8.1 Hz, J = 7.0 Hz,
J = 1.0 Hz); 7.39 (d, 1 H, H(4), J = 7.9 Hz); 7.44 (d, 1 H, H(7),
J = 8.1 Hz); 7.62—7.52 (m, 2 H, H(6´), H(7´)); 7.93—7.99 (m,
3 H, H(3´), H(4´), H(5´)); 8.03 (d, 1 H, H(8´), J = 8.8 Hz);
8.31 (s, 1 H, H(1´)), 9.57 (s, 1 H, NHCO); 11.56 (s, 1 H, NH).
13C NMR (DMSO-d6), δ: 22.9 (Me), 111.4 (C(3a)), 111.4 (C(7)),
118.6 (C(5)), 119.2 (C(4)), 122.1 (C(6)), 124.8 (C(6´)), 125.2
(C(7´)), 126.2 (C(8a´)), 126.3 (C(1´)), 126.7 (C(3´)), 127.7
(C(4´)), 128.0 (C(5´)), 128.2 (C(8´)), 129.3 (C(2)), 131.1
(C(7a)), 132.1 (C(2´)), 133.1 (C(3)), 134.8 (C(4a´)), 169.7
(C=O). MS (ESI), m/z: 323.1160 [M + Na]+. C20H16N2NaO.
Calculated: M = 323.1155. Rf 0.39 (acetone—hexane, 1 : 1).
Rf 0.67 (ethyl acetate—hexane, 1 : 1).
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Received September 23, 2019;
in revised form November 5, 2019;
accepted November 6, 2019
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