Cycloisomerization – a straightforward way to benzo[h]quinolines and benzo[c]acridines

Article abstract of DOI:10.1007/s10593-017-2179-5

[Figure not available: see fulltext.] Cycloisomerization of 3-alkynyl-2-arylpyridines and quinolines offers a straightforward approach to benzo[h]quinolines and benzo[c]-acridines. Substituent at the triple bond governs a choice between transition metal or Br?nsted acid catalysis. A direct electrophilic activation by trifluoromethanesulfonic acid induces an almost quantitative cyclization of the o-aryl(phenylethynyl) fragment. PtCl₂ efficiently catalyzes cyclization of 2-aryl-3-ethynylhetarenes.

Full text of DOI:10.1007/s10593-017-2179-5

DOI 10.1007/s10593-017-2179-5
Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
Cycloisomerization – a straightforward way
to benzo[h]quinolines and benzo[c]acridines
Aleksandr N. Shestakov1, Alena S. Pankova1, Mikhail A. Kuznetsov1*
1 Institute of Chemistry, Saint Petersburg State University,
26 Universitetsky Ave., Saint Petersburg 198504, Russia; е-mail: m.kuznetsov@spbu.ru
Submitted September 25, 2017
Accepted October 25, 2017
Published in Khimiya Geterotsiklicheskikh Soedinenii,
2017, 53(10), 1103–1113
Cycloisomerization of 3-alkynyl-2-arylpyridines and quinolines offers a straightforward approach to benzo[h]quinolines and benzo[c]-
acridines. Substituent at the triple bond governs a choice between transition metal or Brønsted acid catalysis. A direct electrophilic
activation by trifluoromethanesulfonic acid induces an almost quantitative cyclization of the o-aryl(phenylethynyl) fragment. PtCl2
efficiently catalyzes cyclization of 2-aryl-3-ethynylhetarenes.
Keywords: alkynes, benzo[c]acridines, benzo[h]quinolines, pyridines, quinolines, cycloisomerization, synthetic methods.
Compounds with the benzo[h]quinoline and benzo[c]-
acridine cores are valuable classes of heterocycles with a
wide range of applications exhibiting antibacterial,1 wound
healing,2 antioxidant,2 and anticancer activity.3–7 Their
complexes with transition metals and organosilicon com-
pounds were applied in cross-coupling reactions;8,9 bio-
activity10 and fluorescence properties11–13 of these
complexes have been described as well. Considering the
importance of benzoquinoline derivatives, several approa-
ches to their synthesis have been developed. Among them,
methods based on the construction of the central benzene
ring are quite limited, although they allow utilizing readily
available pyridine derivatives.14–20
Cycloisomerization of o-ethynylbiaryls has emerged as
an important tool for the synthesis of fused aromatic
systems. Electrophilic activation21–27 and catalysis with
transition metals28–34 are often used for cyclization. Although
substantial work has been done to investigate and improve
the efficiency of this transformation, for instance, via the
utilization of Au-35–37 or Pt-based38,39 complexes, or by
evaluation of the substrate and catalysts scope and
limitations,40–44 carbocyclic substrates have been involved
in these cyclizations almost exclusively. Reports on
cycloisomerization of heteroaromatic compounds have
appeared in literature only in last years.45–51 Recently, we
have developed a simple and efficient procedure for the
Brønsted acid-mediated cyclization of o-aryl(ethynyl)-
pyrimidines producing benzo[f]quinazolines.52 Here we
present our findings in the cycloisomerization of various
o-aryl(ethynyl)pyridines and quinolines using either transi-
tion metal catalysis or by action of Brønsted acid toward
benzo[h]quinolines and benzo[c]acridines.
Starting 2-aryl-3-ethynylpyridines were prepared from
2,3-dibromopyridine 1 by a sequence of two cross-coupling
reactions (Scheme 1, Table 1). The difference in reactivity
of bromine atoms allows selective arylation in position 2 of
the pyridine ring via the Suzuki coupling at 50°C.53 Next,
the Sonogashira cross coupling was used for the
introduction of the acetylenic moiety. While the reaction
with phenylacetylene proceeded smoothly in DMA at 90°C
forming compounds 3a–j in high yields after 6 h,
trimethylsilylacetylene was completely inert. Solvent and
temperature screening revealed that i-Pr2NH and 80°C
were optimal conditions for the preparation of 2-aryl-
3-(trimethylsilylethynyl)pyridines 4a–j.
TMS group can be easily removed from pyridines 4a–j
by treatment with K2CO3 in a CH2Cl2–MeOH mixture at
room temperature to afford pyridines 5a–j with a terminal
triple bond. For pyridines 5c,h, we demonstrated that the
Sonogashira cross coupling/TMS-deprotection sequence
could be performed in a one-pot fashion without affecting
the overall yield.
Cycloisomerization of ethynylpyridines 5 was first
attempted under conditions reported for o-alkynylbiphenyls
on pyridine 5a as a test compound (Scheme 2, Table 2).28
Pyridine 5a was heated with PtCl2 in toluene at 80°C for
0009-3122/17/53(10)-1103©2017 Springer Science+Business Media New York
1103

Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
Scheme 1
Scheme 2
Table 2. Screening of catalysts for the cyclization
of pyridine 5a into quinoline 6a
Catalyst
Solvent
T,°C
Time, h
Yield, %
(10 mol %)
PtCl2
PtCl2
InCl3
GaCl3
Yb(OTf)3
PtCl2
–
PhMe
PhMe
PhMe
PhMe
PhMe
PhCl
80
20
20
20
20
20
12
4
27
67
110
110
110
110
130
20
Not detected
Not detected
14
65
TfOH
Not detected
Table 1. Yields of 3-alkynyl-2-arylpyridines 2–5 a–j
Yield of compound, %
Ar
20 h, however, the cyclization product 6a was isolated in
low yield. Other Lewis acids, such as InCl3, GaCl3, and
Yb(OTf)3 were ineffective catalysts, and their use led to
slow degradation of the starting material. Treatment of
compound 5a with TfOH also gave no product, but using
PtCl2 (10 mol %) at higher reaction temperature (110°C)
furnished targeted benzo[h]quinoline 6a in 67% yield.
Increasing temperature further to 130°C did not improve
the yield.
2
3
4
5
83
80
85
93
a
78
62
88
83
78
–
94
b
78*
c
d
e
A substrate scope for the PtCl2-catalyzed cyclization of
2-aryl-3-ethynylpyrydines is sufficiently broad and
includes compounds with electron-donating and electron-
withdrawing substituents along with sterically hindered
ones (Scheme 3). Moderately donor alkyl group at the para
position of the phenyl ring promoted the cyclization: the
84
74
95
91
87
89
95
92
Scheme 3
CH
PtCl2 (10 mol %)
N
77
65
93
84
90
86
96
94
f
N
PhMe, 110°C, 20 h
R
5a j
–
R
6a–j
g
6a R = H (67%)
6b R = Et (80%)
6c R = CF3 (55%)*
6d R = F (66%)*
6e R = Cl (63%)*
6f R = OMe (60%)
6g R = NMe2 (54%)**
81
81
78
87
–
81*
93
h
i
N
R
6a–g
81
Me
N
N
N
Me
77
84
85
94
j
Me
6i (80%)**
Cl
6j
(69%)
6h
(57%)**
* 48 h.
** 130°C in chlorobenzene.
* Two-step yield.
1104

Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
yield of 8-ethylbenzo[h]quinoline 6b was 80%. Only ca.
pyrimidine gave the single corresponding spiro product.52
At 0°C, only spiro compound 8 formed from phenyl-
ethynylpyridine 3f in 93% yield (the mechanism of this
ipso cyclization is analogous to that we described for
pyrimidines).52 Protonation of the Me2N group in pyridine
3g appears to cause a complete deactivation of this
substrate toward the cyclization; indeed no target product
was detected in the complex reaction mixture of phenyl-
ethynylpyridine 3g by 1H NMR spectroscopy. TfOH-
promoted reaction is less sensitive to steric factors than
PtCl2-catalyzed process as unsymmetrically substituted
pyridine 3j gave a mixture of isomers 7j and 7j' (cf.
compound 6j, Scheme 3).
The cyclization of halo-substituted substrates 3d,e with
concentrated sulfuric acid instead of TfOH was tested, as
the nature of the acid is known to effect the reaction
outcome (Scheme 5).52 Indeed, pyridine 3d gave a mixture
of compounds 7d and 8 in a ratio 2.5:1 (total yield 73%),
whereas benzo[h]quinazoline 7e was a single product for
pyridine 3e. The latter result differs from the reaction of
similarly substituted 5-(4-chlorophenyl)-4-(phenylethynyl)-
pyrimidine in concentrated sulfuric acid giving an analog
of spiro compound 8 only (see the reaction of phenyl-
ethynylpyridine 3f also, Scheme 4). The pyridine core of
phenylethynylpyridines 3 disfavors ipso cyclization probably
because of the close position of an aryl fragment to the
nitrogen atom. Fluorine atom as a stronger +M substituent
weakens this effect and facilitates formation of spiro
compound 8 from phenylethynylpyridine 3d.
50% conversion was observed in 20 h for electron-deficient
substrates, but prolonged heating (up to 48 h) allowed
isolation of compounds 6c–e in 55–66% yields. This is
consistent with the deactivation of electron-deficient aryl
ring toward an electrophilic attack. Strong electron-
donating methoxy group in 2-aryl-3-ethynylpyrydine 5f
had no influence on the reaction yield. Unexpectedly,
dimethylamino-substituted derivative 5g was almost inert
under these conditions and its cyclization occurred only at
130°С, which might be caused by a strong coordination of
PtCl2 to the Me2N group. Sterically hindered pyridines 5h,i
required 130°C for the successful cyclization as well.
Regioselective cyclization was observed for pyridine 5j
and the single isomer 6j formed via attack of the bulky
PtCl2–triple bond complex on the less hindered ortho
position of the m-chloro-substituted phenyl ring.
In contrast to ethynylpyridines 5a–j, phenylethynyl-
pyridines 3a–j are more convenient targets for the direct
electrophilic activation. Initially we employed TFA–CH2Cl2
system which had been previously reported for pyridine-
based substrates,54 however, phenylethynylpyridine 3a was
inert under these conditions and even when heated in pure
TFA. Recently, we have described the successful
utilization of TfOH for the cyclization of o-alkynyl(aryl)-
pyrimidines,52 and this protocol quantitatively provided
benzo[h]quinoline 7a within 15 min (Scheme 4).
Quinolines 7b–e,h,i were also isolated in excellent yields
regardless of the nature of substituents. 2-(4-Meth-
oxyphenyl)pyridine 3f gave the mixture of the major
benzo[h]quinoline 7f and the minor spiro compound 8,
although similar 5-(4-methoxyphenyl)-4-(phenylethynyl)-
Scheme 5
Ph
Ph
Ph
H2SO4
rt
Scheme 4
N
+
N
N
R
O
R
3d,e
7d (52%)
7e (88%)
8(21%)
–
R = F, 12 h
R = Cl, 0.5 h
As a further test of the applicability of this methodology
to the synthesis of more complex molecules, several
quinoline-based acetylenes were also examined. Substrates
11a–d were prepared from 2-chloroquinoline-3-carb-
aldehydes55 9a–d by the Suzuki cross coupling followed by
treatment of 2-phenylquinoline-3-carbaldehydes 10a–d
with Bestmann–Ohira reagent (Scheme 6, Table 3).
Quinolines 12a,b were obtained by the Sonogashira
reaction of compounds 11a,b with iodobenzene.
Fused benzene ring in the heterocyclic core slightly
reduced reactivity of quinolines compared to pyridines,
though annulated acridines 13 and 14 were obtained in
good to excellent yields (Scheme 7). For cycloisomeriza-
tion of terminal acetylenes 11a–d, PtCl2 catalysis was used
at a slightly higher temperature than for compounds 5a–j.
TfOH-mediated reaction of phenylethynylquinolines 12a,b
was a little slower and completed within 1 h. Further
exploration of this reaction and physical properties of the
resulting compounds will be reported later.
1105

Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
Scheme 6
Scheme 7
Table 3. Yields of quinoline-based substrates 10–12
Yields of compounds, %
R1
10
90
92
94
93
11
53
57
42
39
12
85
84
–
H
a
b
c
6-Me
6-OMe
8-OMe
–
d
In summary, an efficient and simple method to access a
3-Bromo-2-(4-ethylphenyl)pyridine (2b). Yield 409 mg
1
variety of benzo[h]quinolines and benzo[c]acridines by
cycloisomerization of o-alkynyl(aryl)pyridines and quino-
lines is described. Two general protocols have been deve-
loped depending on the substrate: PtCl2 catalytic conditions
are favorable for terminal acetylenes, while TfOH excels
with phenylethynyl-substituted heterocycles. Various
substituents in aryl fragments are tolerated.
(78%), colorless oil. H NMR spectrum, δ, ppm (J, Hz):
1.28 (3H, t, J = 7.6, CH2CH3); 2.72 (2H, q, J = 7.6,
CH2CH3); 7.11 (1H, dd, J = 8.0, J = 4.6, H Py); 7.30 (2H,
d, J = 8.0, H Ph); 7.62 (2H, d, J = 8.0, H Ph); 7.97 (1H, dd,
J = 8.0, J = 1.4, H Py); 8.61 (1H, dd, J = 4.6, J = 1.4,
H Py). 13C NMR spectrum, δ, ppm: 15.5; 28.9; 119.9;
123.1; 127.6; 129.4; 137.1; 141.4; 145.1; 148.2; 158.4.
Found, m/z: 262.0225 [M+H]+. C13H13BrN. Calculated, m/z:
262.0226.
3-Bromo-2-[4-(trifluoromethyl)phenyl]pyridine (2c).
Yield 374 mg (62%), colorless solid, mp 49–50°C (mp 50–
51°C53).
3-Bromo-2-(4-fluorophenyl)pyridine (2d). Yield 423 mg
(84%), colorless solid, mp 72–74°C (mp 73–74°C53).
3-Bromo-2-(4-chlorophenyl)pyridine (2e).56 Yield 395 mg
(74%), colorless oil.
Experimental
1H and 13C NMR spectra were recorded on a Bruker
Avance 400 spectrometer 400 and 101 MHz, respectively)
in CDCl3 and were referenced to the solvent residual
proton (7.26 ppm) and carbon signals (77.16 ppm). High-
resolution mass spectra were recorded on a Bruker Maxis
HRMS-ESI-qTOF spectrometer (electrospray ionization
mode). Melting points were determined on a Stuart SMP30
instrument.
3-Bromo-2-(4-methoxyphenyl)pyridine (2f). Yield
405 mg (77%), colorless solid, mp 60–61°C (mp 61–
62°C53).
Synthesis of 2-aryl-3-bromopyridines 2a–j (General
method). A mixture of MeCN and MeOH (2:1, 15 ml) was
added to a mixture of 2,3-dibromopyridine (1) (474 mg,
2.0 mmol), arylboronic acid (2.1 mmol), K2CO3 (560 mg,
4.0 mmol), PPh3 (52 mg, 10 mol %) and Pd(OAc)2 (23 mg,
5 mol %) in a screw-cap vial. Reaction mixture was flushed
with argon, sealed, and stirred at 50°C for 24 h in an oil
bath. Then the reaction mixture was cooled to room tempe-
rature and filtered through Celite. Filtrate was concentrated
under reduced pressure, the residue was dissolved in CH2Cl2
(20 ml), washed with water (3×10 ml) and dried over
Na2SO4. Solvent was evaporated under reduced pressure,
and the residue was purified by column chromatography on
silica (hexane–EtOAc, 30:1) to provide pure pyridines 2a–j.
3-Bromo-2-phenylpyridine (2a).53 Yield 387 mg
(83%), colorless oil.
4-(3-Bromopyridin-2-yl)-N,N-dimethylaniline (2g).57
Yield 360 mg (65%), yellow gum.
3-Bromo-2-(2-methylphenyl)pyridine (2h).53 Yield
402 mg (81%), colorless oil.
3-Bromo-2-(3,5-dimethylphenyl)pyridine (2i). Yield
1
423 mg (81%), colorless oil. H NMR spectrum, δ, ppm
(J, Hz): 2.38 (6H, s, CH3); 7.07 (1Н, br. s, H Ph); 7.11 (1H,
dd, J = 8.0, J = 4.6, H Py); 7.27 (2Н, br. s, H Ph); 7.97 (1H,
dd, J = 8.0, J = 1.5, H Py); 8.61 (1H, dd, J = 4.6, J = 1.5,
H Py). 13C NMR spectrum, δ, ppm: 21.5; 120.0; 123.2;
127.1; 130.5; 137.6; 139.6; 141.3; 148.1; 158.8. Found, m/z:
262.0223 [M+H]+. C13H13BrN. Calculated, m/z: 262.0226.
3-Bromo-2-(3-chlorophenyl)pyridine (2j). Yield 413 mg
1
(77%), colorless oil. H NMR spectrum, δ, ppm (J, Hz):
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Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
7.16 (1H, dd, J = 8.0, J = 4.6, H Py); 7.37–7.42 (2H, m,
J = 4.8, J = 1.8, H Py). 13C NMR spectrum, δ, ppm: 40.5;
88.6; 94.2; 111.6; 116.7; 120.2; 123.4; 127.5; 128.5 (2C);
130.5; 131.6; 141.2; 148.6; 151.1; 159.5. Found, m/z:
299.1533 [M+H]+. C21H19N2. Calculated, m/z: 299.1543.
2-(2-Methylphenyl)-3-(phenylethynyl)pyridine (3h).58
Yield 105 mg (78%), pale-yellow oil.
H Ar); 7.56–7.59 (1H, m, H Ar); 7.67–7.69 (1H, m, H Ar);
8.00 (1H, dd, J = 8.0, J = 1.5, H Py); 8.63 (1H, dd, J = 4.6,
J = 1.5, H Py). 13C NMR spectrum, δ, ppm: 119.9; 123.8;
127.7; 129.0; 129.4; 129.6; 134.1; 141.3; 141.6; 148.3; 156.9.
Found, m/z: 267.9519 [M+H]+. C11H8BrClN. Calculated, m/z:
267.9523.
2-(3,5-Dimethylphenyl)-3-(phenylethynyl)pyridine (3i).
Yield 123 mg (87%), colorless solid, mp 100–101°C.
1H NMR spectrum, δ, ppm (J, Hz): 2.42 (6H, s, CH3); 7.10
(1Н, br. s, H Ar); 7.22 (1H, dd, J = 7.8, J = 4.8, H Py); 7.31–
7.35 (3H, m, H Ph); 7.39–7.43 (2H, m, H Ph); 7.67 (2Н, br. s,
H Ar); 7.92 (1H, dd, J = 7.8, J = 1.7, H Py); 8.64 (1H, dd,
J = 4.8, J = 1.7, H Py). 13C NMR spectrum, δ, ppm: 21.6;
87.9; 94.7; 117.9; 121.3; 123.1; 127.3; 128.5; 128.7; 130.6;
131.5; 137.4; 139.4; 140.8; 148.6; 160.0. Found, m/z:
284.1435 [M+H]+. C21H18N. Calculated, m/z: 284.1434.
2-(3-Chlorophenyl)-3-(phenylethynyl)pyridine (3j).
Synthesis of 2-aryl-3-(phenylethynyl)pyridines 3a–j
(General method). DMA (5 ml) was added to a mixture of
2-aryl-3-bromopyridine
2
(0.5 mmol), Pd(PPh3)2Cl2
(17.6 mg, 5 mоl %), and CuI (4.8 mg, 5 mоl %) in a screw-
cap vial. Reaction mixture was flushed with argon,
phenylacetylene (56 mg, 0.55 mmоl) and Et3N (0.2 ml,
1.4 mmol) were added, the vial was sealed. The reaction
mixture was stirred at 90°C in an oil bath for 6 h. Then the
reaction mixture was cooled to room temperature, poured
into water (40 ml), and extracted with EtOAc (3×10 ml).
The combined extracts were washed with water (2×5 ml)
and dried over Na2SO4. Solvent was evaporated under
reduced pressure, and the residue was purified by column
chromatography on silica (hexane–EtOAc, 20:1) to provide
pure pyridines 3a–j.
1
Yield 122 mg (84%), brown solid, mp 92–93°C. H NMR
spectrum, δ, ppm (J, Hz): 7.28 (1H, dd, J = 7.8, J = 4.8,
H Py); 7.33–7.37 (3H, m, H Ph); 7.41–7.47 (4H, m, H Ar);
7.91–7.96 (2H, m, H Ar and Py); 8.10–8.11 (1H, m, H Ar);
8.65 (1H, dd, J = 4.8, J = 1.7, H Py). 13C NMR spectrum,
δ, ppm: 87.1; 95.4; 118.2; 122.0; 122.7; 127.7; 128.6;
129.0 (2C); 129.3; 129.6; 131.6; 133.9; 141.0; 141.2;
148.7; 158.1. Found, m/z: 290.0735 [M+H]+. C19H13ClN.
Calculated, m/z: 290.0731.
2-Phenyl-3-(phenylethynyl)pyridine (3a). Yield 102 mg
(80%), brown solid, mp 67–68°C (mp 69°C58).
2-(4-Ethylphenyl)-3-(phenylethynyl)pyridine
(3b).
1
Yield 125 mg (88%), yellow solid, mp 75–76°C. H NMR
spectrum, δ, ppm (J, Hz): 1.30 (3H, t, J = 7.6, CH2CH3);
2.74 (2H, q, J = 7.6, CH2CH3); 7.22 (1H, dd, J = 7.8,
J = 4.8, H Py); 7.31–7.35 (5H, m, H Ar); 7.41–7.45 (2H,
m, H Ar); 7.92 (1H, dd, J = 7.8, J = 1.8, H Py); 7.98–8.01
(2H, m, H Ar); 8.64 (1H, dd, J = 4.8, J = 1.8, H Py).
13C NMR spectrum, δ, ppm: 15.7; 28.9; 87.9; 94.8; 117.8;
121.2; 123.1; 127.6; 128.5; 128.7; 129.4; 131.5; 137.0;
140.9; 145.3; 148.7; 159.7. Found, m/z: 284.1431 [M+H]+.
C21H18N. Calculated, m/z: 284.1434.
Synthesis of 2-aryl-3-(trimethylsilylethynyl)pyridines
4a–j (General method). Diisopropylamine (2.5 ml) was
added to a mixture of 2-aryl-3-bromopyridine 2 (1.0 mmol),
Pd(PPh3)2Cl2 (35 mg, 5 mоl %), and CuI (9.6 mg, 5 mоl %)
in a screw-cap vial. Reaction mixture was flushed with
argon, trimethylsilylacetylene (118 mg, 1.2 mmоl) was
added, the vial was sealed. The reaction mixture was stirred
at 80°C in an oil bath for 4 h. Then the reaction mixture
was cooled to room temperature, solvent was evaporated,
and the residue was purified by column chromatography on
silica (hexane–EtOAc, 20:1) to provide pure pyridines
4a,b,d–g,i,j. Pyridines 4c,h were used for the next step
without isolation and purification.
3-(Phenylethynyl)-2-[4-(trifluoromethyl)phenyl]pyridine
(3c). Yield 134 mg (83%), colorless solid, mp 64–65°C.
1H NMR spectrum, δ, ppm (J, Hz): 7.31 (1H, dd, J = 7.9,
J = 4.6, H Py); 7.33–7.37 (3H, m, H Ph); 7.38–7.42 (2H,
m, H Ph); 7.75 (2H, d, J = 8.2, H Ar); 7.97 (1H, dd, J = 7.9,
J = 1.7, H Py); 8.16 (2H, d, J = 8.2, H Ar); 8.67 (1H, dd,
J = 4.6, J = 1.7, H Py). 13C NMR spectrum, δ, ppm (J, Hz):
2-Phenyl-3-(trimethylsilylethynyl)pyridine (4a).59 Yield
213 mg (85%), pale-yellow oil.
2-(4-Ethylphenyl)-3-(trimethylsilylethynyl)pyridine (4b).
1
1
86.9; 95.4; 118.3; 122.3; 122.6; 124.4 (q, JCF = 272.1);
Yield 218 mg (78%), pale-yellow oil. H NMR spectrum,
3
125.0 (q, JCF = 3.8); 128.7; 129.1; 129.9; 130.9 (q,
δ, ppm (J, Hz): 0.20 (9H, s, CH3); 1.27 (3H, t, J = 7.6,
CH2CH3); 2.71 (2H, q, J = 7.6, CH2CH3); 7.16 (1H, dd,
J = 7.8, J = 4.8, H Py); 7.25–7.28 (2H, m, H Ar); 7.84 (1H,
dd, J = 7.8, J = 1.4, H Py); 7.92–7.97 (2H, m, H Ar); 8.61
(1Н, dd, J = 4.8, J = 1.4, H Py). 13C NMR spectrum,
δ, ppm: –0.3; 15.7; 28.9; 100.7; 103.3; 117.6; 121.0; 127.4;
129.5; 136.7; 141.4; 145.3; 148.8; 160.0. Found, m/z:
280.1508 [M+H]+. C18H22NSi. Calculated, m/z: 280.1516.
2-(4-Fluorophenyl)-3-(trimethylsilylethynyl)pyridine
(4d). Yield 234 mg (87%), pale-yellow oil. 1H NMR
spectrum, δ, ppm (J, Hz): 0.20 (9H, s, CH3); 7.08–7.15
(2H, m, H Ar); 7.19 (1H, dd, J = 7.8, J = 4.8, H Py); 7.85
(1H, dd, J = 7.8, J = 1.8, H Py); 7.98–8.03 (2H, m, H Ar);
8.60 (1Н, dd, J = 4.8, J = 1.8, H Py). 13C NMR spectrum,
2JCF = 32.4); 131.6; 141.1; 143.0; 148.9; 158.2. Found, m/z:
324.0988 [M+H]+. C20H13F3N. Calculated, m/z: 324.0995.
2-(4-Fluorophenyl)-3-(phenylethynyl)pyridine (3d). Yield
130 mg (95%), colorless solid, mp 71–72°C (mp 72°C58).
2-(4-Chlorophenyl)-3-(phenylethynyl)pyridine (3e).
Yield 131 mg (91%), colorless solid, mp 119–121°C
(mp 121°C58).
2-(4-Methoxyphenyl)-3-(phenylethynyl)pyridine (3f).58
Yield 133 mg (93%), yellow oil.
N,N-Dimethyl-4-[3-(phenylethynyl)pyridin-2-yl]aniline
1
(3g). Yield 125 mg (84%), yellow oil. H NMR spectrum,
δ, ppm (J, Hz): 3.04 (6H, s, N(CH3)2); 6.79–6.84 (2H, m,
H Ar); 7.13 (1H, dd, J = 7.8, J = 4.8, H Py); 7.31–7.36 (3H,
m, H Ph); 7.45–7.52 (2H, m, H Ph); 7.87 (1H, dd, J = 7.8,
J = 1.8, H Py); 8.04–8.12 (2H, m, H Ar); 8.60 (1H, dd,
2
δ, ppm (J, Hz): –0.3; 101.1; 102.8; 114.8 (d, JCF = 21.5);
3
4
117.7; 121.4; 131.5 (d, JCF = 8.3); 135.4 (d, JCF = 3.2);
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Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
1
141.5; 148.8; 158.9; 163.4 (d, JCF = 248.4). Found, m/z:
270.1106 [M+H]+. C16H17FNSi. Calculated, m/z: 270.1109.
2-(4-Chlorophenyl)-3-(trimethylsilylethynyl)pyridine
(4e). Yield 254 mg (89%), pale-yellow oil. 1H NMR
spectrum, δ, ppm (J, Hz): 0.21 (9H, s, CH3); 7.20 (1H, dd,
J = 7.8, J = 4.8, H Py); 7.38–7.43 (2H, m, H Ar); 7.85 (1H,
dd, J = 7.8, J = 1.8, H Py); 7.94–8.00 (2H, m, H Ar); 8.61
(1Н, dd, J = 4.8, J = 1.8, H Py). 13C NMR spectrum, δ, ppm:
–0.3; 101.4; 101.7; 117.7; 121.6; 128.1; 130.9; 135.1; 137.7;
141.6; 148.9; 158.6. Found, m/z: 286.0817 [M+H]+.
C16H17ClNSi. Calculated, m/z: 286.0813.
3-Ethynyl-2-phenylpyridine (5a). Yield 83 mg (93%),
colorless solid, mp 70–72°C (mp 72°C59).
2-(4-Ethylphenyl)-3-ethynylpyridine (5b). Yield 97 mg
(94%), yellow oil. 1H NMR spectrum, δ, ppm (J, Hz): 1.28
(3H, t, J = 7.6, CH2CH3); 2.72 (2H, q, J = 7.6, CH2CH3);
3.25 (1H, s, ≡CH); 7.19 (1H, dd, J = 7.8, J = 4.8, H Py);
7.28–7.30 (2H, m, H Ar); 7.87–7.91 (3H, m, H Py and Ar);
8.64 (1Н, dd, J = 4.8, J = 1.8, H Py). 13C NMR spectrum,
δ, ppm: 15.5; 28.9; 81.8; 82.9; 116.6; 121.1; 127.6; 129.3;
136.6; 142.0; 145.3; 149.1; 160.4. Found, m/z: 208.1125
[M+H]+. C15H14N. Calculated, m/z: 208.1121.
2-(4-Methoxyphenyl)-3-(trimethylsilylethynyl)pyridine
(4f). Yield 253 mg (90%), pale-yellow oil. 1H NMR
spectrum, δ, ppm (J, Hz): 0.21 (9H, s, CH3); 3.86 (3H, s,
OCH3); 6.93–6.99 (2H, m, H Ar); 7.14 (1H, dd, J = 7.8,
J = 4.8, H Py); 7.83 (1H, dd, J = 7.8, J = 1.8, H Py); 7.98–
8.05 (2H, m, H Ar); 8.59 (1Н, dd, J = 4.8, J = 1.8, H Py).
13C NMR spectrum, δ, ppm: –0.2; 55.5; 100.6; 103.4;
113.2; 117.2; 120.8; 130.9; 131.9; 141.6; 148.8; 159.5;
160.4. Calculated, m/z: 282.1309 [M+H]+. C17H20NOSi.
Found, m/z: 282.1309.
3-Ethynyl-2-[4-(trifluoromethyl)phenyl]pyridine (5c).
Two-step yield 193 mg (78%), colorless solid, mp 78–79°C.
1H NMR spectrum, δ, ppm (J, Hz): 3.28 (1H, s, ≡CH); 7.28
(1H, dd, J = 7.8, J = 4.8, H Py); 7.72 (2H, d, J = 8.1, H Ar);
7.93 (1H, dd, J = 7.8, J = 1.7, H Py); 8.07 (2H, d, J = 8.1,
H Ar); 8.68 (1H, dd, J = 4.8, J = 1.7, H Py). 13C NMR
spectrum, δ, ppm (J, Hz): 80.9; 83.6; 117.1; 122.0; 124.2
1
3
(q, JCF = 272.1); 124.9 (q, JCF = 3.8); 129.6; 130.8 (q,
2JCF = 32.4); 142.0; 142.4; 149.2; 158.7. Found, m/z:
248.0684 [M+H]+. C14H9F3N. Calculated, m/z: 248.0682.
3-Ethynyl-2-(4-fluorophenyl)pyridine (5d). Yield 94 mg
N,N-Dimethyl-4-[3-(trimethylsilylethynyl)pyridin-2-yl]-
1
1
aniline (4g). Yield 253 mg (86%), orange oil. H NMR
(95%), colorless solid, mp 74–75°C. H NMR spectrum,
spectrum, δ, ppm (J, Hz): 0.23 (9H, s, CH3); 3.02 (6H, s,
N(CH3)2); 6.73–6.78 (2H, m, H Ar); 7.06 (1H, dd, 7.8,
J = 4.8, H Py); 7.80 (1H, dd, J = 7.8, J =1.8, H Py); 8.01–
8.09 (2H, m, H Ar); 8.56 (1Н, dd, J = 4.8, J = 1.8, H Py).
13C NMR spectrum, δ, ppm: –0.1; 40.5; 100.0; 104.1;
111.4; 116.4; 119.9; 127.2; 130.5; 141.8; 148.7; 151.1;
159.6. Found, m/z: 295.1629 [M+H]+. C18H23N2Si.
Calculated, m/z: 295.1625.
δ, ppm (J, Hz): 3.26 (1H, s, ≡CH); 7.11–7.17 (2H, m,
H Ar); 7.22 (1H, dd, J = 7.8, J = 4.8, H Py); 7.90 (1H, dd,
J = 7.8, J = 1.8, H Py); 7.93–7.98 (2H, m, H Ar); 8.64 (1Н,
dd, J = 4.8, J = 1.8, H Py). 13C NMR spectrum, δ, ppm
2
(J, Hz): 81.5; 83.2; 115.1 (d, JCF = 21.6); 116.7; 121.5;
3
4
131.4 (d, JCF = 8.4); 135.3 (d, JCF = 3.2); 142.1; 149.2;
1
159.3; 163.4 (d, JCF = 248.7). Found, m/z: 198.0710
[M+H]+. C13H9FN. Calculated, m/z: 198.0714.
2-(3,5-Dimethylphenyl)-3-(trimethylsilylethynyl)pyridine
(4i). Yield 226 mg (81%), pale-yellow oil. 1H NMR
spectrum, δ, ppm (J, Hz): 0.19 (9H, s, CH3); 2.38 (6H, s,
CH3); 7.05 (1Н, br. s, H Ar); 7.17 (1H, dd, J = 7.8, J = 4.8,
H Py); 7.61 (2Н, br. s, H Ar); 7.85 (1Н, dd, J = 7.8, J = 1.6,
H Py); 8.61 (1Н, dd, J = 4.8, J = 1.6, H Py). 13C NMR
spectrum, δ, ppm: –0.2; 21.5; 100.5; 103.1; 117.7; 121.1;
127.2; 130.6; 137.3; 139.1; 141.7; 148.7; 160.2. Found, m/z:
280.1514 [M+H]+. C18H22NSi. Calculated, m/z: 280.1516.
2-(3-Chlorophenyl)-3-(trimethylsilylethynyl)pyridine
2-(4-Chlorophenyl)-3-ethynylpyridine (5e). Yield 98 mg
1
(92%), colorless solid, mp 85–86°C. H NMR spectrum,
δ, ppm (J, Hz): 3.27 (1H, s, ≡CH); 7.23 (1H, dd, J = 7.8,
J = 4.8); 7.40–7.46 (2H, m, H Ar); 7.88–7.94 (3H, m, H Ar
and Py); 8.65 (1Н, dd, J = 4.8, J = 1.7, H Py). 13C NMR
spectrum, δ, ppm: 81.3; 83.4; 116.8; 121.7; 128.3; 130.8;
135.2; 137.6; 142.1; 149.3; 159.1. Found, m/z: 214.0421
[M+H]+. C13H9ClN. Calculated, m/z: 214.0418.
3-Ethynyl-2-(4-methoxyphenyl)pyridine (5f). Yield
1
100 mg (96%), colorless solid, mp 59–60°C. H NMR
1
(4j). Yield 242 mg (85%), yellow oil. H NMR spectrum,
spectrum, δ, ppm (J, Hz): 3.25 (1H, s, ≡CH); 3.86 (3H, s,
OCH3); 6.96–7.01 (2H, m, H Ar); 7.17 (1H, dd, J = 7.8,
J = 4.8, H Py); 7.87 (1H, dd, J = 7.8, J = 1.8, H Py); 7.92–
7.98 (2H, m, H Ar); 8.62 (1H, dd, J = 4.8, J = 1.8, H Py).
13C NMR spectrum, δ, ppm: 55.4; 81.9; 82.8; 113.5; 116.3;
120.9; 130.8; 131.8; 142.1; 149.1; 159.9; 160.4. Found, m/z:
210.0910 [M+H]+. C14H12NO. Calculated, m/z: 210.0913.
4-(3-Ethynylpyridin-2-yl)-N,N-dimethylaniline (5g).
Yield 104 mg (94%), yellow oil. 1H NMR spectrum,
δ, ppm (J, Hz): 3.02 (6H, s, N(CH3)2); 3.27 (1H, s, ≡CH);
6.75–6.81 (2H, m, H Ar); 7.10 (1H, dd, J = 7.8, J = 4.8,
H Py); 7.84 (1H, dd, J = 7.8, J = 1.8, H Py); 7.93–8.00 (2H,
m, H Ar); 8.60 (1H, dd, J = 4.8, J = 1.8, H Py). 13C NMR
spectrum, δ, ppm: 40.4; 82.4; 82.5; 111.5; 115.6; 120.1;
127.0; 130.4; 142.2; 149.1; 151.0; 160.2. Found, m/z:
223.1235 [M+H]+. C15H15N2. Calculated, m/z: 223.1230.
3-Ethynyl-2-(2-methylphenyl)pyridine (5h). Two-step
yield 156 mg (81%), yellow oil. 1H NMR spectrum, δ, ppm
δ, ppm (J, Hz): 0.21 (9H, s, CH3); 7.22 (1H, dd, J = 7.8,
J = 4.8, H Py); 7.35–7.40 (2H, m, H Ar); 7.85–7.90 (2H,
m, H Py and Ar); 8.04–8.06 (1H, m, H Ar); 8.62 (1H, dd,
J = 4.8, J = 1.7, H Py). 13C NMR spectrum, δ, ppm: –0.3;
101.7; 102.3; 118.0; 121.8; 127.7; 129.0; 129.2; 129.6;
133.8; 140.9; 141.5; 148.9; 158.4. Found, m/z: 286.0807
[M+H]+. C16H17ClNSi. Calculated, m/z: 286.0813.
Synthesis of 2-aryl-3-ethynylpyridines 5a–j (General
method). A mixture of 2-aryl-3-(trimethylsilylethynyl)-
pyridine 4 (0.5 mmol) and K2CO3 (70 mg, 0.5 mmol) was
stirred in a mixture MeOH–CH2Cl2, 2:1 (3 ml) at room
temperature for 20 min. Upon completion, the reaction
mixture was filtered through Celite, the filtrate was diluted
with diethyl ether (20 ml), washed with water (3×10 ml),
and dried over Na2SO4. Solvent was evaporated, and the
residue was purified by column chromatography on silica
(hexane–EtOAc, 15:1) to provide pure pyridines 5.
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Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
2
(J, Hz): 2.23 (3H, s, CH3); 3.07 (1H, s, ≡CH); 7.23–7.34
127.6; 130.1 (q, JCF = 32.4); 133.0; 133.6; 136.1; 146.0;
149.6. Found, m/z: 248.0686 [M+H]+. C14H9F3N. Calcu-
lated, m/z: 248.0682.
(5H, m, H Ar and Py); 7.89 (1H, dd, J = 7.8, J = 1.7, H Py);
8.65 (1H, dd, J = 4.8, J = 1.7, H Py). 13C NMR spectrum,
δ, ppm: 19.7; 80.7; 82.7; 118.7; 121.6; 125.5; 128.6; 129.3;
130.2; 136.1; 139.4; 140.6; 148.8; 162.6. Found, m/z:
194.0965 [M+H]+. C14H12N. Calculated, m/z: 194.0964.
2-(3,5-Dimethylphenyl)-3-ethynylpyridine (5i). Yield
96 mg (93%), yellow oil. 1H NMR spectrum, δ, ppm (J, Hz):
2.39 (6H, s, CH3); 3.23 (1H, s, ≡CH); 7.07 (1H, br. s,
H Ar); 7.20 (1H, dd, J = 7.8, J = 4.8, H Py); 7.55 (2H, br. s,
H Ar); 7.89 (1H, d, J = 7.8, H Py); 8.64 (1H, d, J = 4.8,
H Py). 13C NMR spectrum, δ, ppm: 21.5; 81.7; 82.8; 116.9;
121.3; 127.1; 130.7; 137.6; 139.1; 141.9; 149.1; 160.8.
Found, m/z: 208.1125 [M+H]+. C15H14N. Calculated, m/z:
208.1121.
8-Fluorobenzo[h]quinoline (6d). Yield 26 mg (66%),
colorless solid, mp 63–64°C. H NMR spectrum, δ, ppm
1
(J, Hz): 7.44–7.54 (3H, m, H benzoquinoline); 7.68–7.75
(2H, m, H benzoquinoline); 8.15 (1H, dd, J = 8.0, J = 1.7,
H benzoquinoline); 8.99 (1H, dd, J = 4.4, J = 1.7, H benzo-
4
quinoline); 9.30 (1H, dd, J = 9.1, JHF = 5.8, H benzo-
quinoline). 13C NMR spectrum, δ, ppm (J, Hz): 112.0 (d,
2JCF = 20.9); 116.2 (d, JCF = 23.6); 121.8; 125.9 (d,
2
5JCF = 1.1); 126.9; 127.1 (d, 4JCF = 3.8); 127.3 (d, 3JCF = 9.0);
5
3
128.3 (d, JCF = 1.7); 135.1 (d, JCF = 9.2); 136.0; 146.7;
1
149.3; 162.7 (d, JCF = 247.9). Found, m/z: 198.0716
[M+H]+. C13H9FN. Calculated, m/z: 198.0714.
2-(3-Chlorophenyl)-3-ethynylpyridine (5j). Yield 100 mg
8-Chlorobenzo[h]quinoline (6e). Yield 27 mg (63%),
colorless solid, mp 109–110°C. 1H NMR spectrum, δ, ppm
(J, Hz): 7.52 (1H, dd, J = 8.0, J = 4.4, H benzoquinoline);
7.64–7.70 (3H, m, H benzoquinoline), 7.86 (1H, d, J = 2.1,
H benzoquinoline); 8.15 (1H, dd, J = 8.0, J = 1.7, H benzo-
quinoline); 8.99 (1H, dd, J = 4.4, J = 1.7, H benzo-
quinoline); 9.22 (1H, d, J = 8.8, H benzoquinoline).
13C NMR spectrum, δ, ppm: 122.1; 126.3; 126.4; 126.8
(2C); 126.9; 127.7; 130.0; 134.4; 134.6; 136.0; 146.3; 149.3.
Found, m/z: 214.0423 [M+H]+. C13H9ClN. Calculated, m/z:
214.0418.
1
(94%), colorless solid, mp 54–55°C. H NMR spectrum,
δ, ppm (J, Hz): 3.29 (1H, s, ≡CH); 7.25 (1H, dd, J = 7.8,
J = 4.8, H Py); 7.36–7.42 (2H, m, H Ar); 7.83–7.86 (1H,
m, H Ar); 7.91 (1H, dd, J = 7.8, J = 1.7, H Py); 7.94–7.97
(1H, m, H Ar); 8.66 (1H, dd, J = 4.8, J = 1.7, H Py).
13C NMR spectrum, δ, ppm: 81.1; 83.6; 117.0; 121.9;
127.6; 129.1; 129.3; 129.5; 134.1; 140.8; 142.1; 149.3;
158.8. Found, m/z: 214.0419 [M+H]+. C13H9ClN. Calcu-
lated, m/z: 214.0418.
Synthesis of benzo[h]quinolines 6a–j (General method).
PtCl2 (5.3 mg, 10 mоl %) was added to a solution of
pyridine 5a–j (0.2 mmol) in toluene (chlorobenzene for
pyridines 5g–i) (0.5 ml) in a screw-cap vial. Reaction
mixture was flushed with argon, the vial was sealed and
heated with stirring in an oil bath at 110°C (130°C for
pyridines 5g–i) for 20 h (48 h for pyridines 5с–e). Solvent
was evaporated under reduced pressure, and the residue
was purified by column chromatography on silica (hexane–
EtOAc, 15:1) to provide pure quinolines 6.
8-Methoxybenzo[h]quinoline (6f). Yield 25 mg (60%),
yellow oil. 1H NMR spectrum, δ, ppm (J, Hz): 3.98 (3H, s,
OCH3); 7.00 (1H, d, J = 2.4, H benzoquinoline); 7.27 (1H,
dd, J = 9.0, J = 2.4, H benzoquinoline); 7.37 (1H, dd,
J = 7.9, J = 4.4, H benzoquinoline); 7.57 (1H, d, J = 8.9,
H benzoquinoline); 7.66 (1H, d, J = 8.9, H benzoquinoline);
8.07 (1H, dd, J = 7.9, J = 1.7, H benzoquinoline); 8.91 (1H,
dd, J = 4.4, J = 1.7, H benzoquinoline); 9.10 (1H, d,
J = 9.0, H benzoquinoline). 13C NMR spectrum, δ, ppm:
40.7; 107.6; 115.0; 120.1; 122.4; 124.9; 125.6; 125.7; 127.8;
135.6; 136.0; 147.1; 148.6; 150.6. Found, m/z: 210.0907
[M+H]+. C14H12NO. Calculated, m/z: 210.0913.
Benzo[h]quinoline (6а). Yield 24 mg (67%), colorless
solid, mp 50–51°C (mp 51–52°C60).
8-Ethylbenzo[h]quinoline (6b). Yield 33 mg (80%),
yellowish oil. 1H NMR spectrum, δ, ppm (J, Hz): 1.39 (3H,
t, J = 7.6, CH2CH3); 2.90 (2H, q, J = 7.6, CH2CH3); 7.48
(1H, dd, J = 8.0, J = 4.3, H benzoquinoline); 7.60–7.66
(2H, m, H benzoquinoline); 7.71 (1H, br. s, H benzo-
quinoline); 7.77 (1H, d, J = 8.8, H benzoquinoline); 8.14
(1H, dd, J = 8.0, J = 1.3, H benzoquinoline); 8.99 (1H, dd,
J = 4.3, J = 1.3, H benzoquinoline); 9.21 (1H, d, J = 8.4,
H benzoquinoline). 13C NMR spectrum, δ, ppm: 15.7; 29.1;
121.5; 124.5; 125.4; 126.2; 126.3; 127.8; 128.0; 129.8;
134.0; 135.8; 144.6; 146.8; 148.9. Found, m/z: 208.1118
[M+H]+. C15H14N. Calculated, m/z: 208.1121.
N,N-Dimethylbenzo[h]quinolin-8-amine (6g). Yield
24 mg (54%), orange solid, mp 110–111°C. 1H NMR
spectrum, δ, ppm (J, Hz): 3.12 (6H, s, N(CH3)2); 7.26 (1H,
d, J = 2.8, H benzoquinoline); 7.37 (1H, dd, J = 9.0,
J = 2.8, H benzoquinoline); 7.45 (1H, dd, J = 8.0, J = 4.4,
H benzoquinoline); 7.65 (1H, d, J = 8.8, H benzo-
quinoline); 7.73 (1H, d, J = 8.8, H benzoquinoline); 8.13
(1H, dd, J = 8.0, J = 1.8, H benzoquinoline); 8.96 (1H, dd,
J = 4.4, J = 1.8, H benzoquinoline); 9.20 (1H, d, J = 9.0,
H benzoquinoline). 13C NMR spectrum, δ, ppm: 55.6;
108.1; 117.6; 121.0; 125.4; 126.1; 126.2; 126.3; 127.4;
135.3; 135.9; 146.8; 149.1; 159.8. Found, m/z: 223.1224
[M+H]+. C15H15N2. Calculated, m/z: 223.1230.
8-(Trifluoromethyl)benzo[h]quinoline (6c). Yield 27 mg
1
(55%), colorless solid, mp 75–76°C. H NMR spectrum,
δ, ppm (J, Hz): 7.58 (1H, dd, J = 8.0, J = 4.4, H benzo-
quinoline); 7.76 (1H, d, J = 8.9, H benzoquinoline); 7.84
(1H, d, J = 8.9, H benzoquinoline); 7.92 (1H, d, J = 8.6,
H benzoquinoline); 8.17–8.22 (2H, m, H benzoquinoline);
10-Methylbenzo[h]quinoline (6h). Yield 22 mg (57%),
colorless solid, mp 73–74°C. H NMR spectrum, δ, ppm
1
(J, Hz): 3.37 (3H, s, CH3); 7.48 (1H, dd, J = 8.0, J = 4.3,
H benzoquinoline); 7.55–7.59 (2H, m, H benzoquinoline);
7.66 (1H, d, J = 8.7, H benzoquinoline); 7.78–7.81 (2H, m,
H benzoquinoline); 8.16 (1H, dd, J = 8.0, J = 1.8, H benzo-
quinoline); 9.03 (1H, dd, J = 4.3, J = 1.8, H benzo-
quinoline). 13C NMR spectrum, δ, ppm: 27.3; 120.7; 125.6;
3
9.04 (1H, dd, J = 4.4, J = 1.5, H benzoquinoline); 9.41
(1H, d, J = 8.6, H benzoquinoline). 13C NMR spectrum,
3
δ, ppm (J, Hz): 122.9; 123.0 (q, JCF = 3.3); 124.5 (q,
3
1JCF = 272.2); 125.3 (q, JCF = 4.3); 125.7; 127.0; 127.3;
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Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
126.8; 127.4; 127.6; 128.9; 130.1; 131.3; 135.3; 135.4;
149.5. Found, m/z: 324.0986 [M+H]+. C20H13F3N. Calcu-
138.9; 147.3; 149.2. Found, m/z: 194.0966 [M+H]+.
C14H12N. Calculated, m/z: 194.0964.
lated, m/z: 324.0995.
8-Fluoro-6-phenylbenzo[h]quinoline (7d). Yield 51 mg
(93%), colorless solid, mp 115–116°C. 1H NMR spectrum,
δ, ppm (J, Hz): 7.45–7.57 (8H, m, H Ph and benzo-
quinoline); 7.66 (1H, s, H benzoquinoline); 8.17 (1H, dd,
J = 8.0, J = 1.7, H benzoquinoline); 9.00 (1H, dd, J = 4.4,
J = 1.7, H benzoquinoline); 9.55 (1H, dd, J = 8.0,
4JHF = 6.0, H benzoquinoline). 13C NMR spectrum, δ, ppm
7,9-Dimethylbenzo[h]quinoline (6i). Yield 33 mg
1
(80%), colorless solid, mp 77–78°C. H NMR spectrum,
δ, ppm (J, Hz): 2.62 (3H, s, CH3); 2.74 (3H, s, CH3); 7.39
(1H, br. s, H benzoquinoline), 7.50 (1H, dd, J = 8.0,
J = 4.4, H benzoquinoline); 7.65 (1H, d, J = 9.1, H benzo-
quinoline); 7.98 (1H, d, J = 9.1, H benzoquinoline); 8.16
(1H, dd, J = 8.0, J = 1.7, H benzoquinoline); 8.98–9.02
(2H, m, H benzoquinoline). 13C NMR spectrum, δ, ppm:
19.7; 22.0; 121.7; 122.1; 123.9; 124.1; 126.3; 130.6; 131.3;
131.9; 134.3; 135.9; 136.8; 146.8; 148.7. Found, m/z:
208.1114 [M+H]+. C15H14N. Calculated, m/z: 208.1121.
9-Chlorobenzo[h]quinoline (6j). Yield 26 mg (61%),
colorless solid, mp 118–119°C. 1H NMR spectrum, δ, ppm
(J, Hz): 7.52 (1H, dd, J = 8.0, J = 4.4, H benzoquinoline);
7.60–7.66 (2H, m, H benzoquinoline); 7.74 (1H, d, J = 8.8,
H benzoquinoline); 7.80 (1H, d, J = 8.5, H benzoquinoline);
8.14 (1H, dd, J = 8.0, J = 1.3, H benzoquinoline); 8.98 (1H,
dd, J = 4.4, J = 1.3, H benzoquinoline); 9.26 (1H, d,
J = 1.9, H benzoquinoline). 13C NMR spectrum, δ, ppm:
122.4; 124.1; 125.7; 126.8; 127.1; 128.8; 129.3; 131.9;
132.7; 133.4; 135.9; 145.7; 149.2. Found, m/z: 214.0411
[M+H]+. C13H9ClN. Calculated, m/z: 214.0418.
2
2
(J, Hz): 111.1 (d, JCF = 22.6); 116.0 (d, JCF = 23.7);
5
3
122.1; 125.5 (d, JCF = 1.0); 127.1; 127.5 (d, JCF = 9.0);
5
128.0; 128.6 (d, JC-F = 1.6); 128.7; 129.9; 134.5 (d,
3JCF = 8.8); 136.0; 139.3 (d, JCF = 3.8); 139.8; 146.0;
4
1
149.3; 162.8 (d, JCF = 247.3). Found, m/z: 274.1030
[M+H]+. C19H13FN. Calculated, m/z: 274.1027.
8-Chloro-6-phenylbenzo[h]quinoline (7e). Yield 55 mg
(95%), colorless solid, mp 129–130°C. 1H NMR spectrum,
δ, ppm (J, Hz): 7.47–7.58 (6H, m, H Ph and benzo-
quinoline); 7.64 (1H, s, H benzoquinoline); 7.69 (1H, dd,
J = 8.8, J = 2.1, H benzoquinoline); 7.87 (1H, d, J = 2.1,
H benzoquinoline); 8.16 (1H, dd, J = 8.0, J = 1.7, H benzo-
quinoline); 9.00 (1H, dd, J = 4.4, J = 1.7, H benzoquinoline);
9.36 (1H, d, J = 8.8, H benzoquinoline). 13C NMR
spectrum, δ, ppm: 122.4; 125.6; 126.0; 126.6; 127.1; 127.6;
128.1; 128.7; 130.0; 130.2; 133.9; 134.7; 136.1; 139.1; 139.6;
145.8; 149.3. Found, m/z: 290.0723 [M+H]+. C19H13ClN.
Calculated, m/z: 290.0731.
Cyclization of 2-aryl-3-(phenylethynyl)pyridines 3a–j
(General method). A solution of pyridine 3a–j (0.2 mmol)
in TfOH (0.5 ml) was stirred at room temperature for 15 min.
The reaction mixture was poured into cold water (20 ml)
and extracted with CH2Cl2 (2×5 ml). The combined
extracts were washed with water (2×5 ml) and dried over
Na2SO4. Solvent was evaporated under reduced pressure,
and the residue was purified by column chromatography on
silica (hexane–EtOAc, 15:1) to provide pure products.
6-Phenylbenzo[h]quinoline (7а). Yield 49 mg (96%),
colorless solid, mp 139–140°C (mp 140–141°C61).
8-Methoxy-6-phenylbenzo[h]quinoline (7f). Yield 37 mg
1
(65%), colorless solid, mp 86–87°C. H NMR spectrum,
δ, ppm (J, Hz): 3.83 (3H, s, OCH3); 7.30 (1H, d, J = 2.5,
H benzoquinoline); 7.39 (1H, dd, J = 9.0, J = 2.5, H benzo-
quinoline); 7.45–7.59 (6H, m, H Ph and benzoquinoline);
7.61 (1H, s, H benzoquinoline); 8.15 (1H, dd, J = 8.0,
J = 1.4, H benzoquinoline); 8.98 (1H, dd, J = 4.4, J = 1.4,
H benzoquinoline); 9.34 (1H, d, J = 9.0, H benzo-
quinoline). 13C NMR spectrum, δ, ppm: 55.5; 107.7; 116.9;
121.3; 125.1; 126.6; 126.7; 127.8; 128.6; 129.9; 134.5; 136.1;
139.5; 140.4; 148.8; 159.9. Found, m/z: 286.1222 [M+H]+.
C20H16NO. Calculated, m/z: 286.1226.
8-Ethyl-6-phenylbenzo[h]quinoline (7b). Yield 54 mg
1
(95%), colorless solid, mp 95–96°C. H NMR spectrum,
δ, ppm (J, Hz): 1.29 (3H, t, J = 7.6, CH2CH3); 2.81 (2H, q,
J = 7.6, CH2CH3); 7.46–7.59 (7H, m, H Ph and benzo-
quinoline); 7.64 (1H, dd, J = 8.4, J = 1.6, H benzoquinoline);
7.72 (1H, br. s, H benzoquinoline); 8.14 (1H, dd, J = 8.0,
J = 1.7, H benzoquinoline); 9.00 (1H, dd, J = 4.4, J = 1.7,
H benzoquinoline); 9.35 (1H, d, J = 8.4, H benzoquinoline).
13C NMR spectrum, δ, ppm: 15.8; 29.4; 121.8; 124.9 (2C);
125.7; 126.0; 127.7(2C); 128.5; 130.1 (2C); 133.0; 135.9;
139.8; 140.6; 144.6; 146.4; 148.8. Found, m/z: 284.1430
[M+H]+. C21H18N. Calculated, m/z: 284.1434.
6'-Phenyl-4H-spiro[cyclohexa-2,5-diene-1,7'-cyclopenta-
[b]pyridin]-4-one (8). Yield 14 mg (26%), 38 mg (93%,
isolated as a single product when the reaction was carried
out at 0°C on 0.15 mmol scale), colorless solid, mp 184–
1
85°C. H NMR spectrum, δ, ppm (J, Hz): 6.56–6.60 (2H,
m, =CH); 6.68–6.72 (2H, m, =CHCO); 7.24 (1H, dd,
J = 7.6, J = 5.0, H Py); 7.30–7.36 (3H, m, H Ph); 7.46 (1H,
s, CH=CPh); 7.56–7.59 (2H, m, H Ph); 7.71 (1H, dd,
J = 7.6, J = 1.5, H Py); 8.40 (1H, dd, J = 5.0, J = 1.5,
H Py). 13C NMR spectrum, δ, ppm: 61.0; 123.5; 126.1;
127.7; 128.9; 129.0; 129.2; 132.6; 134.0; 138.3; 147.4;
147.6; 147.7; 162.6; 186.1. Found, m/z: 272.1079 [M+H]+.
C19H14NO. Calculated, m/z: 272.1070.
6-Phenyl-8-(trifluoromethyl)benzo[h]quinoline (7c).
Yield 58 mg (90%), yellowish solid, mp 120–121°C.
1H NMR spectrum, δ, ppm (J, Hz): 7.49–7.62 (6H, m, H Ph
and benzoquinoline); 7.72 (1H, s, H benzoquinoline); 7.95
(1H, dd, J = 8.6, J = 1.5, H benzoquinoline); 8.18–8.23
(2H, m, H benzoquinoline); 9.05 (1H, dd, J = 4.4, J = 1.7,
H benzoquinoline); 9.55 (1H, d, J = 8.6, H benzoquinoline).
10-Methyl-6-phenylbenzo[h]quinoline (7h). Yield 52 mg
(97%), yellowish solid, mp 145–146°C. 1H NMR spectrum,
δ, ppm (J, Hz): 3.45 (3H, s, CH3); 7.47–7.55 (7H, m, H Ph
3
13C NMR spectrum, δ, ppm (J, Hz): 122.9 (q, JCF = 3.0);
and benzoquinoline); 7.59–7.61 (2H, m, H benzo-
3
1
123.2; 123.8 (q, JCF = 4.3); 124.5 (q, JCF = 272.4);
126.0; 126.9; 127.3; 128.3; 128.8; 130.0 (2C, q,
2JCF = 32.2); 132.2; 134.0; 136.1; 139.4; 139.9; 145.5;
quinoline); 7.80 (1H, d, J = 8.0, H benzoquinoline); 8.15
(1H, dd, J = 8.0, J = 1.9, H benzoquinoline); 9.06 (1H, dd,
J = 4.3, J = 1.9, H benzoquinoline). 13C NMR spectrum,
1110

Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
δ, ppm: 27.8; 120.9; 125.3; 126.4; 127.0; 127.2; 127.6;
was flushed with argon, sealed, and stirred at 120°C for 3 h
in an oil bath. Then the reaction mixture was cooled to
room temperature, poured into water (50 ml), and extracted
with EtOAс (3×10 ml). Extracts were washed with water
(2×15 ml) and dried over Na2SO4. Solvent was evaporated
under reduced pressure, and the residue was purified by
column chromatography on silica (hexane–CHCl3, 10:1) to
provide pure carbaldehydes 10a–d.
128.4; 130.2; 130.4; 131.3; 134.4; 135.4; 139.1; 140.5;
141.3; 147.2; 148.7. Found, m/z: 270.1270 [M+H]+.
C20H16N. Calculated, m/z: 270.1277.
7,9-Dimethyl-6-phenylbenzo[h]quinoline (7i). Yield
1
50 mg (88%), colorless solid, mp 172–173°C. H NMR
spectrum, δ, ppm (J, Hz): 2.04 (3H, s, CH3); 2.62 (3H, s,
CH3); 7.30 (1H, br. s, H benzoquinoline); 7.38–7.44 (5H,
m, H Ph); 7.46 (1H, s, H benzoquinoline); 7.50 (1H, dd,
J = 8.0, J = 4.4, H benzoquinoline); 8.09 (1H, dd, J = 8.0,
J = 1.7, H benzoquinoline); 8.99 (1H, dd, J = 4.4, J = 1.7,
H benzoquinoline); 9.22 (1H, br. s, H benzoquinoline).
13C NMR spectrum, δ, ppm: 21.7; 25.0; 122.1; 122.8;
125.3; 127.1; 127.3; 128.0; 129.4; 129.6; 133.2; 134.3;
135.5; 135.6; 136.7; 140.0; 144.9; 146.4; 148.6. Found, m/z:
284.1430 [M+H]+. C21H18N. Calculated, m/z: 284.1434.
7-Chloro-6-phenylbenzo[h]quinoline (7j). Yield 37 mg
(64%), colorless solid, 140–141°C. 1H NMR spectrum,
δ, ppm (J, Hz): 7.38–7.45 (5H, m, H Ph); 7.55 (1H, dd,
J = 8.0, J = 4.4, H benzoquinoline); 7.61 (1H, s, H benzo-
quinoline); 7.62–7.66 (1H, m, H benzoquinoline); 7.71
(1H, dd, J = 7.6, J = 1.5, H benzoquinoline); 8.12 (1H, dd,
J = 8.0, J = 1.7, H benzoquinoline); 9.02 (1H, dd, J = 4.4,
J = 1.7, H benzoquinoline); 9.50 (1H, dd, J = 8.1, J = 1.5,
H benzoquinoline). 13C NMR spectrum, δ, ppm: 122.8;
124.3; 125.4; 127.1; 127.2; 127.8; 129.4; 129.5; 130.0;
131.8; 131.9; 134.6; 135.7; 138.5; 143.3; 146.0; 149.4.
Found, m/z: 290.0733 [M+H]+. C19H13ClN. Calculated, m/z:
290.0731.
2-Phenylquinoline-3-carbaldehyde (10а). Yield 210 mg
(90%), colorless solid, mp 96–97°C (mp 98°C62).
6-Methyl-2-phenylquinoline-3-carbaldehyde (10b).
Yield 227 mg (92%), yellowish solid, mp 119–121°C
(mp 120–121°C62).
6-Methoxy-2-phenylquinoline-3-carbaldehyde (10c).
Yield 247 mg (94%), yellowish solid, mp 129–131°C
(mp 130°C62).
8-Methoxy-2-phenylquinoline-3-carbaldehyde (10d).
Yield 245 mg (93%), yellowish solid, mp 159–160°C.
1H NMR spectrum, δ, ppm (J, Hz): 4.10 (3H, s, OCH3);
7.19–7.22 (1H, m, H quinoline); 7.48–7.60 (5H, m, H Ph
and quinoline); 7.68–7.72 (2H, m, H Ph); 8.81 (1H, s,
H quinoline); 10.19 (1H, s, CHO). 13C NMR spectrum,
δ, ppm: 56.4; 110.7; 121.1; 127.7; 127.8; 128.2; 128.8; 129.4;
130.7; 138.0 (2C); 141.6; 155.6; 159.3; 191.8. Found, m/z:
264.1017 [M+H]+. C17H14NО2. Calculated, m/z: 264.1019.
Synthesis of 3-ethynyl-2-phenylquinolines 11a–d
(General method). A mixture of 2-phenylquinoline-3-carb-
aldehyde 10a–d (1 mmol), K2CO3 (280 mg, 2 mmol) and
diethyl 1-diazo-2-oxopropylphosphonate (264 mg, 1.2 mmol)
in MeOH (8 ml) was stirred at room temperature overnight.
Solvent was evaporated under reduced pressure, and the
residue was purified by column chromatography on silica
(hexane–CHCl3, 20:1) to provide pure quinolines 11a–d.
3-Ethynyl-2-phenylquinoline (11а). Yield 121 mg
(53%), colorless solid, mp 99–100°C. 1H NMR spectrum,
δ, ppm (J, Hz): 3.27 (1H, s, ≡CH); 7.47–7.58 (4H, m, H Ph
and quinoline); 7.72–7.76 (1H, m, H quinoline); 7.80 (1H,
d, J = 8.1, H quinoline); 8.00–8.03 (2H, m, H Ph); 8.16
(1H, d, J = 8.5, H quinoline); 8.44 (1H, s, H quinoline).
13C NMR spectrum, δ, ppm: 81.9; 82.8; 115.1; 126.2; 127.2
(2C); 128.1; 129.2; 129.7 (2C); 130.8; 139.5; 142.4; 147.2;
159.6. Found, m/z: 230.0970 [M+H]+. C17H12N. Calculated,
m/z: 230.0964.
3-Ethynyl-6-methyl-2-phenylquinoline (11b). Yield
138 mg (57%), colorless solid, mp 107–108°C. 1H NMR
spectrum, δ, ppm (J, Hz): 2.55 (3H, s, CH3); 3.25 (1H, s,
≡CH); 7.45–7.58 (5H, m, H Ph and quinoline); 7.98–8.01
(2H, m, H Ph); 8.04 (1H, d, J = 8.5, H quinoline); 8.34
(1H, s, H quinoline). 13C NMR spectrum, δ, ppm: 22.7;
82.1; 82.6; 115.0; 125.9; 126.2; 128.1; 129.0; 129.4; 129.6;
133.1; 137.2; 139.6; 141.7; 145.9; 158.7. Found, m/z:
244.1119 [M+H]+. C18H14N. Calculated, m/z: 244.1121.
3-Ethynyl-6-methoxy-2-phenylquinoline (11c). Yield
109 mg (42%), yellow solid, mp 109–110°C. 1H NMR
spectrum, δ, ppm (J, Hz): 3.26 (1H, s, ≡CH); 3.94 (3H, s,
OCH3); 7.04 (1H, d, J = 2.7, H quinoline); 7.39 (1H, dd,
J = 9.2, J = 2.7, H quinoline); 7.44–7.51 (3H, m, H Ph);
7.97–8.00 (2H, m, H Ph); 8.04 (1H, d, J = 9.2, H quino-
line); 8.32 (1H, s, H quinoline). 13C NMR spectrum,
9-Chloro-6-phenylbenzo[h]quinoline (7j'). Yield 15 mg
(26%), colorless solid, mp 158–159°C. 1H NMR spectrum,
δ, ppm (J, Hz): 7.48–7.58 (7H, m, H Ph and benzo-
quinoline); 7.62 (1H, s, H benzoquinoline); 7.84 (1H, d,
J = 8.8, H benzoquinoline); 8.18 (1H, dd, J = 8.0, J = 1.5,
H benzoquinoline); 8.99–9.02 (1H, m, H benzoquinoline);
9.40 (1H, d, J = 2.2, H benzoquinoline). 13C NMR
spectrum, δ, ppm: 122.8; 124.3; 126.1; 126.5; 128.0; 128.1;
128.7 (2C); 130.0; 131.1; 133.1; 133.5; 136.0; 139.6;
139.9; 145.3; 149.1. Found, m/z: 290.0730 [M+H]+.
C19H13ClN. Calculated, m/z: 290.0731.
Treatment of 2-aryl-3-(phenylethynyl)pyridines with
sulfuric acid (General method). A solution of pyridine
3d,e (0.2 mmol) in concentrated H2SO4 (98%, 0.5 ml) was
stirred at room temperature for 12 h (compound 3d) or 0.5 h
(compound 3e). The reaction mixture was poured into cold
water (20 ml) and extracted with CH2Cl2 (2×5 ml). The
combined extracts were washed with water (2×5 ml) and
dried over Na2SO4. Solvent was evaporated under reduced
pressure, and the residue was purified by column chromato-
graphy on silica (hexane–EtOAc, 15:1) to provide pure
products. Mixture of quinoline 7d (52%) and compound 8
(21%) was obtained from pyridine 3d; quinoline 7e (88%)
formed as a single product from pyridine 3e.
Synthesis of 2-phenylquinoline-3-carbaldehydes 10a–d
(General method). A mixture of DMA and water (4:1,
10 ml) was added to a mixture of 2-chloroquinoline-3-carb-
aldehyde 9a–d (1 mmol), phenylboronic acid (128 mg,
1.05 mmol), K2CO3 (280 mg, 2.0 mmol), and Pd(PPh3)4
(56 mg, 5 mol %) in a screw-cap vial. Reaction mixture
1111

Chemistry of Heterocyclic Compounds 2017, 53(10), 1103–1113
δ, ppm: 55.7; 82.1; 82.7; 104.4; 115.3; 123.6; 127.2; 128.1;
7.60–7.63 (1H, m, H benzoacridine); 7.67–7.74 (3H, m,
H benzoacridine); 7.75–7.80 (1H, m, H benzoacridine);
7.85–7.89 (1H, m, H benzoacridine); 8.63 (1H, s, H benzo-
acridine); 9.55–9.58 (1H, m, H benzoacridine). 13C NMR
spectrum, δ, ppm: 56.5; 107.3; 119.9; 125.6(2C); 125.8;
126.2; 127.4; 127.9; 128.2; 128.3; 129.1; 131.9; 134.0;
135.1; 140.4; 146.8; 155.6. Found, m/z: 260.1063 [M+H]+.
C18H14NO. Calculated, m/z: 260.1070.
Synthesis of 5-phenylbenzo[c]acridines 14a,b (General
method). A solution of quinoline 12a,b (0.2 mmol) in
TfOH (0.5 ml) was stirred at room temperature for 1 h. The
reaction mixture was poured into cold water (20 ml) and
extracted with CH2Cl2 (2×5 ml). The combined extracts
were washed with water (2×5 ml) and dried over Na2SO4.
Solvent was evaporated under reduced pressure, and the
residue was purified by column chromatography on silica
(hexane–CHCl3, 15:1) to provide pure acridines 14a,b.
5-Phenylbenzo[c]acridine (14а). Yield 57 mg (93%),
yellowish solid, mp 110–112°C (mp 111–112°C61).
9-Methyl-5-phenylbenzo[c]acridine (14b). Yield 61 mg
(96%), yellowish solid, mp 131–132°C. 1H NMR spectrum,
δ, ppm (J, Hz): 2.60 (3H, s, CH3); 7.47–7.68 (8H, m, H Ph
and benzoacridine); 7.74–7.81 (2H, m, H benzoacridine);
7.87 (1H, d, J = 8.0, H benzoacridine); 8.30 (1H, d, J = 8.7,
H benzoacridine); 8.51 (1H, s, H benzoacridine); 9.63 (1H,
d, J = 8.0, H benzoacridine). 13C NMR spectrum, δ, ppm:
21.9; 124.9; 125.5; 126.2; 126.3; 126.6; 127.2; 127.5;
127.7; 128.5; 128.8; 129.6; 130.0; 132.1; 132.5; 133.3;
134.1; 135.9; 139.4; 140.4; 146.7; 146.9. Found, m/z:
320.1441 [M+H]+. C24H18N. Calculated, m/z: 320.1434.
128.9; 129.6; 131.2; 139.6; 141.0; 143.5; 157.2; 158.3.
Found, m/z: 260.1063 [M+H]+. C18H14NO. Calculated, m/z:
260.1070.
3-Ethynyl-8-methoxy-2-phenylquinoline (11d). Yield
101 mg (39%), yellow solid, mp 101–103°C. 1H NMR
spectrum, δ, ppm (J, Hz): 3.27 (1H, s, ≡CH); 4.06 (3H, s,
OCH3); 7.07 (1H, d, J = 7.7, H quinoline); 7.36 (1H, d,
J = 8.1, H quinoline); 7.43–7.49 (4H, m, H Ph and
quinoline); 8.01–8.04 (2H, m, H Ph); 8.39 (1H, s, H quinoline).
13C NMR spectrum, δ, ppm: 56.2; 81.9; 83.0; 109.1; 115.7;
118.9; 127.3; 127.4; 128.0; 129.0; 129.9; 139.0; 139.6;
142.3; 155.6; 158.4. Found, m/z: 260.1065 [M+H]+.
C18H14NO. Calculated, m/z: 260.1070.
Synthesis of 2-phenyl-3-(phenylethynyl)quinolines 12a,b
(General method). MeCN (5 ml) was added to a mixture of
3-ethynyl-2-phenylquinoline 11a,b (0.5 mmol), Pd(PPh3)2Cl2
(17.6 mg, 5 mоl %) and CuI (4.8 mg, 5 mоl %) in a screw-
cap vial. Reaction mixture was flushed with argon,
iodobenzene (112 mg, 0.55 mmоl) and Et3N (0.17 ml,
1.25 mmol) were added, the vial was sealed; and the
reaction mixture was stirred at 80°C in an oil bath for 6 h.
Then it was cooled to room temperature, poured into water
(40 ml) and extracted with EtOAc (3×10 ml). The
combined extracts were washed with water (2×5 ml) and
dried over Na2SO4. Solvent was evaporated under reduced
pressure, and the residue was purified by column
chromatography on silica (hexane–CHCl3, 15:1) to provide
pure quinolines 12a,b.
2-Phenyl-3-(phenylethynyl)quinoline (12а).63 Yield
130 mg (85%), dark-yellow amorphous solid.
The Supplementary information file containing optimi-
zation of the Sonogashira reaction between pyridine 2a and
TMS-acetylene and copies of 1H and 13C{1H} NMR spectra
of all compounds is available from the journal website at
http://link.springer.com/journal/10593.
6-Methyl-2-phenyl-3-(phenylethynyl)quinoline (12b).
Yield 134 mg (84%), yellow solid, mp 131–132°C.
1H NMR spectrum, δ, ppm (J, Hz): 2.56 (3H, s, CH3); 7.30–
7.44 (5H, m, H Ph); 7.46–7.58 (5H, m, H Ph and
quinoline); 8.02–8.09 (3H, m, H Ph and quinoline); 8.35
(1H, s, H quinoline). 13C NMR spectrum, δ, ppm: 22.8;
88.3; 94.5; 116.2; 123.2; 126.0; 126.5; 128.0; 128.6; 128.7;
129.0; 129.4; 129.7; 131.5; 132.8; 137.1; 139.6; 140.1;
145.7; 158.6. Found, m/z: 320.1437 [M+H]+. C24H18N.
Calculated, m/z: 320.1434.
This research was supported by the Ministry of Educa-
tion and Science of the Russian Federation (grant of the
President of the Russian Federation no. MK-5965.2016.3).
NMR and HRMS analyses were performed at the Saint
Petersburg State University Center for Magnetic
Resonance Resource and Center for Chemical Analysis and
Materials Research.
Synthesis of benzo[c]acridines 13a–d (General method).
A mixture of quinoline 11a–d (0.2 mmol) and PtCl2
(5.3 mg, 10 mоl %) in toluene (0.5 ml) was flushed with
argon in screw-cap vial, sealed, and heated with stirring in
an oil bath at 120°C for 20 h. Solvent was evaporated
under reduced pressure, and the residue was purified by
column chromatography on silica (hexane–CHCl3, 15:1) to
provide pure acridines 13a–d.
The authors thank Dr. Alexey Fedorov (ETH Zurich) for
his help in the preparation of this manuscript.
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Benzo[c]acridine (13а). Yield 27 mg (59%), colorless
solid, mp 107–109°C (mp 108°C64).
9-Methylbenzo[c]acridine (13b). Yield 30 mg (62%),
yellowish solid, mp 126–127°C (mp 126°C65).
9-Methoxybenzo[c]acridine (13c). Yield 30 mg (58%),
yellow solid, mp 154–155°C (mp 155°C66).
11-Methoxybenzo[c]acridine (13d). Yield 31 mg
(60%), colorless solid, mp 115–117°C. 1H NMR spectrum,
δ, ppm (J, Hz): 4.21 (3H, s, OCH3); 7.10–7.14 (1H, m,
H benzoacridine); 7.48–7.53 (1H, m, H benzoacridine);
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