Sterically crowded heterocycles. IX. New α,β-unsaturated ketones containing imidazo[1,2-a]quinoline, imidazo[2,1-a]-isoquinoline, benzo[h]imidazo[1,2-a]quinoline and imidazo[1,2-a]-1,10-phenanthroline moieties

Article abstract of DOI:10.1135/cccc19971599

(Z)-1,3-Diphenyl-3-(2-phenylimidazo[1,2-a]heteroaryl)prop-2-en-1-ones 2-6 and isomeric [1-heteroaryl-3,5-diphenylpyrrol-2-yl]phenylmethanones 17-20 were prepared by the ferricyanide oxidation of quaternary pyridinium salts 12-16. Axial chirality and helicity of the molecules of 4 and 6 are discussed using various energy data obtained by the quantum chemical PM3 method.

Full text of DOI:10.1135/cccc19971599

Sterically Crowded Heterocycles
1599
STERICALLY CROWDED HETEROCYCLES. IX. NEW α,β-UNSATURATED
KETONES CONTAINING IMIDAZO[1,2-a]QUINOLINE, IMIDAZO[2,1-a]-
ISOQUINOLINE, BENZO[h]IMIDAZO[1,2-a]QUINOLINE AND
IMIDAZO[1,2-a]-1,10-PHENANTHROLINE MOIETIES
1,
2,
Stanislav BOHM *, Tomas STRNAD, Iveta RUPPERTOVA and Josef KUTHAN *
Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6,
Czech Republic; e-mail: 1 stanislav.bohm@vscht.cz, 2 kuthanj@vscht.cz
Received March 11, 1997
Accepted May 20, 1997
(Z)-1,3-Diphenyl-3-(2-phenylimidazo[1,2-a]heteroaryl)prop-2-en-1-ones 2–6 and isomeric [1-hetero-
aryl-3,5-diphenylpyrrol-2-yl]phenylmethanones 17–20 were prepared by the ferricyanide oxidation of
quaternary pyridinium salts 12–16. Axial chirality and helicity of the molecules of 4 and 6 are dis-
cussed using various energy data obtained by the quantum chemical PM3 method.
Key words: Imidazo[1,2-a]quinolines; Imidazo[2,1-a]isoquinolines; Benzo[h]imidazo[1,2-a]quinolines;
Imidazo[1,2-a]-1,10-phenanthrolines; Ferricyanide oxidation; Pyridinium salts; Axial chirality; Helicity.
An earlier reexamination1 of products formed2 by ferricyanide oxidation of 1-sub-
stituted 2,4,6-triphenylpyridinium salts led to the conclusion that the compound iso-
lated after the reaction with 1-(quinolin-2-yl)-2,4,6-triphenylpyridinium perchlorate
was undoubtedly imidazo[1,2-a]quinoline 1. Substitution patterns in 1 and its molecular
structure quite analogous to corresponding 2,3-disubstituted imidazo[1,2-a]pyridines3
make it possible to conclude that the molecule of 1 is chiral due to the restricted rota-
tion around the C1–C3′ bond. In connection with our interest in sterically crowded
heterocyclic systems, we have tried to apply our extension of the Decker oxidation4 to
the synthesis of isomeric imidazo[2,1-a]isoquinoline 2 and its methyl derivative 3. To
examine effects of the 1,2-annelation in 1-like molecules, the oxidative preparation of
compounds 4–6 containing 2-phenylbenzo[h]imidazo[1,2-a]quinoline and 2-phenyl-
imidazo[1,2-a]-1,10-phenanthroline has been also attempted. Some chemical transfor-
mations of the products demonstrating their molecular chirality have been carried out,
too. In addition, approximate rotation barriers of compounds 4 and 6 have been calcu-
lated at the semiempirical PM3 level.
* The author to whom correspondence should be addressed.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1600
Bohm, Strnad, Ruppertova, Kuthan:
All preparative experiments started from heteroaromatic amines 7–11 which were
converted to corresponding quaternary pyridinium salts 12–16 in high yields by heating
with 2,4,6-triphenylpyrylium perchlorate in ethanol (Table I). Pyridinium salts 12–16
were subjected to the oxidation with potassium ferricyanide in the presence of potas-
sium hydroxide in aqueous ethanol using the usual procedure5. The results are given in
Table II. Except for 1-(isoquinolin-1-yl)pyridinium perchlorate 12 affording the ex-
pected ketone 2, in all other cases the 1,3,3-trisubstituted (Z)-prop-2-en-1-ones 3–6 are
accompanied by isomeric pyrrole derivatives 17–20 which correspond to typical prod-
ucts from simple 1-substituted 2,4,6-triphenylpyridinium salts4. It might be assumed
that the four-ring fused system in 4 and 5 arises with certain steric difficulties and
therefore the competing formation of isomeric compounds 17 and 18, possessing only
4
9
5
3a
N
R
10
8
7
N
2
Ph
COPh
5a
10a
10b
6
7
N
1
2
6a
9a
1’
Ph
COPh
3’
N
6
2’
9
3
Ph
8
5
1’
3’
2’
Ph
R = H
R = Me
1,
3,
2
R
4
4
5
5
3a
N
2
R
6
R
H
X
3
Ph
COPh
5a
6a
10b
N
N
1
4
5
6
CH
6
7
7
2
Y
11b
10a
1’
Me CH
H
3’
11a
8
X
2’
10
N
X
Ph
7a
8
11
9
9
10
9-19
R
X
Y
4-6
Me
4
9
H
CH NH
2
2
2
5
8
4
5
8
4a
8a
3
3
2
Me CH NH
H
H
Me CH
H
H
10
11
14
15
16
17
18
19
6
6
7
N
NH
A
7
N
N
1
Y
CH
1
Y
A
N
A
Y = NH
Y = A
Y = NH
2
Y = A
Y = B
7,
12,
8,
13,
20,
2
CH
B
Me CH
H
B
N
B
Ph
4’
3’
4
Ph
2’
3a
3’
4’
5’
N
5
6
2
5’
6’
A =
Ph
B =
Ph
COPh
1’
ClO
4
N
1
Ph
COPh
N
2’
1’
N
Ph
7
3’
2’
Ph
21
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1601
the less fused three-ring subsystem, would be preferred. Contrary to the conclusion, the
aza analog of 4 and 5, ketone 6, was found to be only the minor product besides the
predominant isomeric pyrrole derivative 19 in the oxidation of 1-(1,10-phenanthrolin-
2-yl) substituted pyridinium perchlorate 16. Because the conversion is only negligibly
influenced by temperature and inert atmosphere (Table II) and a detailed mechanism
has not yet been known4, only different coordination effects of the 1,10-phenanthroline
moieties in both the competing pathways leading to products 6 and 19 might be ex-
pected.
Molecular structure of all investigated compounds has been verified using elemental
1
analyses (Tables I and III) as well as H and 13C NMR spectra. Thus, pyridinium per-
chlorates 12–16 exhibit proton chemical shifts typical of such type of quaternary salts3.
The signals at δ 8.14 to 8.19 assigned to the ortho protons at the 4′-phenyl groups can
be found in most cases in addition to characteristic singlets of the 3′,5′-protons. Chemi-
cal shifts were almost entirely assigned not only to the position 1 or 2 in the 1′-hetero-
aryl groups but also to all carbons of the pyridinium ring in fragment A.
The pyrrole fragment B in compounds 17–20 can be readily recognized in the 1H NMR
spectra by the occurrence of the characteristic singlets at δ 6.6 to 6.7 of the 4′-protons
and signals at δ 7.7 to 7.8 assigned most probably to the ortho protons in the 5′-phenyl
TABLE I
Yields and physical properties of perchlorates 12–16
Calculated/Found
M.p., °C
Yield, %
Formula
M.w.
Compound
% C
% H
% Cl
% N
12
13
14
15
16c
219–221a C32H23ClN2O4
84 535.0
261–262b C33H35ClN2O4
77 549.0
284–285b C36H25ClN2O4
99 584.2
312–314b C37H27ClN2O4
88 598.2
189–191d C35H26ClN3O5
73 604.1
71.84
71.55
4.33
4.44
6.62
6.35
5.24
5.18
72.19
72.06
4.59
4.68
6.46
6.25
5.10
5.13
73.95
73.68
4.31
4.30
5.99
6.28
4.79
4.75
74.23
74.20
4.55
4.52
5.85
6.00
4.68
4.96
69.59
69.65
4.34
4.23
5.87
5.90
6.96
7.04
a
b
d
From ethanol; from ethanol–nitromethane; c monohydrate; from dimethyl sulfoxide–ethanol–water.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1602
Bohm, Strnad, Ruppertova, Kuthan:
groups in agreement with earlier findings1. Analogously, the 4′-carbons are seen in the
13C NMR spectra at δ ≈112.7 and the presence of the carbonyl groups is proved by
signals at δ 188 to 190.
The interpretation of the spectral characteristics of ketones 2–6 was found to be more
difficult and only partial assignments could be accomplished empirically (see Ex-
1
perimental) using earlier complete interpretations6 of H and 13C NMR spectra of a
more simple 21. More general assignments of 13C signals are compared in Table IV.
Some down-field shifted signals of compounds 3–6 in comparison with those of the
standard 21 may be explained by more extensive π-electron currents in the more fused
subfragments.
All studied ketones 2–6 are evidently axially chiral because of restricted rotation
around the 3-3′ or 1-3′ bonds. For example, compound 3 can be reduced to mixtures of
diastereoisomeric α,β-unsaturated alcohols7. In addition, a through-space repulsion be-
tween the 1- and 11-atomic centres might cause a helical shape of the fused four-ring
system in 4–6 as the second chirality element. Although the phenomenon is well known
in the hydrocarbon chemistry of helicenes, only limited number of corresponding aza
analogues have been investigated8. Therefore, some PM3 calculations of molecules 4
and 6 were performed to estimate realistic geometries of the species. The torsion angle
Φ (formula 22) was used as an axial chirality criterion while the angle Ψ (formula 23)
as a measure of the helicity degree.
Plots of PM3-calculated heats of formation Hf of molecules 4 and 6 versus the tor-
sion angle Φ are shown in Figs 1 and 2. Four more or less developed energy minima
a–d are seen in both the cases. They may be attributed to four conformers 4a–4d and
6a–6d. The curves surprisingly involve almost discontinuous drops of energy at certain
TABLE II
Comparison of products obtained by ferricyanide oxidation of quaternary perchlorates 12–16 at 78 °C
Reaction time
Perchlorate
Ketone
Yield, %
Pyrrole
Yield, %
min
12
13a
14
15
16
16
5
10
10
12
12
90b
2
3
4
5
6
6
52
86
21
20
77
73
–
–
20
17
18
19
19
8
76
78
21
23
a
b
A yield of 75% of ketone 1 has been reported2 from analogous non-methylated pyridinium salt;
at 0 °C.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1603
Φ-values. The analysis of the problem has shown that these extreme energy changes are
caused by jump-like inversions of helicity during relaxation of the molecular systems.
Thus, the restricted rotation around the C1–C3′ bonds and the helicity of the fused
π-electron systems operate together affecting final shapes of the molecules 4 and 6. As
a matter of fact, although the isomeric species 4a–4d and 6a–6d differ negligibly in
their heats of formation Hf (Table V), all exhibit well-marked helicities (Ψ = 8.0–18.8°).
Φ
Ψ
22
23
Considering the recent findings3,9, it may be expected that any chirality change is
mainly associated with the C1–C3′ rotation barrier. The PM3 model of ketone 4 involves
two higher barriers b → c and d → a (22 and 26 kcal/mol) conserving probably the
axial chirality and two additional lower barriers a → b and c → d (7 and 9 kcal/mol)
conjoint mainly to the changes of helicity (Fig. 1). On the other hand, the barriers b → c
and c → d are little developed in the PM3 model of ketone 6 and only the rotation
barriers a → b and d → a (24 and 27 kcal/mol) can be clearly interpreted (Fig. 2). The
185
190
H
H
175
180
170
165
175
170
165
160
d
d
a
b
160
155
c
a
b
c
0
60
FIG. 2
120
180
240
300
360
Φ, °
0
60
120
180
240
300
360
Φ, °
FIG. 1
Dependence of the PM3-calculated heats of for-
mation for 4 on the torsion angle Φ (see for-
mula 22)
Dependence of the PM3-calculated heats of for-
mation for 6 on the torsion angle Φ (see for-
mula 22)
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1604
Bohm, Strnad, Ruppertova, Kuthan:
differences may be attributed to smaller steric requirements of the free electron pair at
N11 in comparison with the C11–H bond.
EXPERIMENTAL
The temperature data are uncorrected. Melting points were determined on a Boetius block. NMR
spectra (δ, ppm; J, Hz; CDCl3 solutions) were taken on a GEMINI 300 HC instrument at 297 K. The
1
working frequency was 300 MHz for H and 75 MHz for 13C. HPLC analyses were performed using
an Ecom LCP 4000 chromatograph with LCD 2082 UV/VIS detector. Commercional Silufol and
Alufol plates (Kavalier Sazava, Czech Republic) were used for TLC.
TABLE III
Characteristics of ferricyanide oxidation products 2–6 and 17–20
Calculated/Found
M.p., °C
solvent
Formula
M.w.
Compound
% C
% H
% N
2
3a
4
153–154
ether
C32H22N2O
450.5
85.31
85.42
4.92
4.88
6.22
6.02
107–110b
C35H30N2O2
510.2
82.33
82.10
5.92
6.00
5.49
5.47
ethanol–heptane
242–246b
C36H24N2O
500.6
86.38
86.41
4.83
4.94
5.60
5.60
ethanol–heptane
5
250–253b
C37H26N2O
514.6
86.36
86.65
5.09
5.22
5.44
5.42
ethanol–heptane
6c
17
18
19
20
133–136
C35H25N3O2
519.6
80.91
80.66
4.85
4.85
8.09
7.88
ethanol–heptane
203–205
C36H24N2O
500.6
86.38
86.63
4.83
4.87
5.60
5.55
heptane–toluene
213–215
C37H26N2O
514.6
86.36
86.53
5.09
5.32
5.44
5.57
ethanol–toluene
191–193
C35H23N3O
501.6
83.81
83.60
4.62
4.78
8.38
8.31
heptane–toluene
174–175
C33H24N2O
464.6
85.32
85.13
5.21
5.26
6.03
5.90
heptane–toluene
a
b
c
Monoethanolate; decomposition; monohydrate.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1605
TABLE IV
Comparison of selected chemical shifts in the 13C NMR spectra of ketones 3–6 and 21
Assignment
3
4
5
6
21a
C4
117.30
125.35
127.95
130.06
130.22
132.76
138.37
138.60
144.22
144.32
145.38
193.36
117.36
125.06
127.95
129.67
129.80
133.05
138.31
138.38
145.26
148.00
148.16
190.91
116.97
125.05
127.81
129.62
129.66
132.97
138.39
138.48
145.41
147.74
147.89
190.91
119.25
117.27
–
C5a
125.39
b
C2′
127.97
129.05
130.23
132.14
137.48
137.73
141.49
145.50
144.69
190.89
m-Ph1′
p-Ph3′
p-Ph1′
i-Ph1′,3′
i-Ph1′,3′
C3′
129.61
b
132.23
138.71
139.03
146.60
146.87
148.19
191.41
C1
C3a
C1′
a
b
Taken from ref.3; the signal is overlapped.
TABLE V
PM3-calculated conformers of ketones 4 and 6
Dihedral anglesa
Compound
∆Hf, kcal/mol
Φ, °
Ψ, °
4a
4b
4c
4d
6a
6b
6c
6d
158.9
156.3
156.4
156.9
162.1
163.2
163.2
163.2
55.8
121.8
237.5
289.3
76.7
+18.8
–18.6
+18.5
–19.8
+8.8
247.5
280.0
305.0
+9.0
–8.0
–10.0
a
See formulae 22 and 23.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1606
Bohm, Strnad, Ruppertova, Kuthan:
(Z)-1,3-Diphenyl-3-(2-phenylimidazo[2,1-a]isoquinolin-3-yl)prop-2-en-1-one (2)
A solution of potassium ferricyanide (1.6 g) and potassium hydroxide (0.4 g) in water (8 ml) was
portionwise added to a boiling solution of pyridinium salt 12 (0.8 g, 1.5 mmol) in ethanol (80 ml)
during 1 min. After 5 min refluxing, the reaction mixture was poured into cold water (100 ml) and
extracted with chloroform (4 × 16 ml). Collected organic extracts were washed with water (2 × 50 ml),
dried over magnesium sulfate and evaporated in vacuo. The residue was subjected a column chroma-
tography (80 g of silica gel, CHCl3) affording a yellow oil which crystallized on treatment with
ether. The yield was 0.35 g (52%) (see Table III). 1H NMR spectrum: 6.97 d, 1 H, J = 9.0 (H-6);
7.14–7.77 m, 20 H (H-2′, H-7, H-8, H-9, H-10 and Ph); 8.72 d, 1 H, J = 9.0 (H-5). 13C NMR spec-
trum: 112.63 CH, 119.82 C, 122.06 CH, 122.62 CH, 122.91 C, 126.67 CH, 127.12 CH, 127.17 CH,
127.53 CH, 128.07 CH, 128.08 CH, 128.14 CH, 128.18 CH, 128.39 CH, 128.46 CH, 129.04 CH,
129.31 C, 130.33 CH, 132.87 CH, 132.87 CH, 133.66 C, 137.34 C, 137.45 C, 140.49 C, 141.97 C,
189.64 C (C-3).
(Z)-3-(5-Methyl-2-phenylimidazo[1,2-a]quinolin-1-yl)-1,3-diphenylprop-2-en-1-one (3)
and 1-(4-Methylquinolin-2-yl)-3,5-diphenyl-1H-pyrrol-2-yl)phenylmethanone (20)
A solution of potassium ferricyanide (1.8 g, 5.37 mmol) and potassium hydroxide (4.4 g, 78.7 mmol)
in water (10 ml) was added to a stirred and refluxed suspension of perchlorate 13 in ethanol (50 ml).
After 10 min the reaction mixture was poured onto crushed ice (200 g), extracted with 3 × 25 ml of
dichloromethane and the collected organic extracts were dried with sodium sulfate and evaporated.
Crystallization of the residue from ethanol afforded the major portion of ketone 3. 1H NMR spec-
trum: 2.61 s, 3 H (Me-5); 7.08 dd, 2 H, J = 8.0 and 7.5 (Ph); 7.14–7.25 m, 3 H (H-2′ and Ph); 7.29 ddd,
1 H, J = 8.0, 7.5 and 1.5 (H-8); 7.32–7.48 m, 8 H (Ph); 7.54–7.65 m, 5 H (H-4, H-7 and Ph); 7.86 ddd,
1 H, J ≈ 8.0, ≈ 4.0 and ≈ 1.0 (H-6); 8.18 ddd, 1 H, J ≈ 8.0, ≈ 4.0 and ≈ 1.0 (H-9). 13C NMR spec-
trum: 20.02 CH3 (C-5), 117.30 CH (C-4), 117.72 CH, 120.51 C (C-2), 124.82 CH, 125.35 C, 126.04 CH,
127.95 CH (C-2′), 127.98 2 × CH (Ph), 128.42 2 × CH (Ph), 128.48 2 × CH (Ph), 128.58 2 × CH (Ph),
128.63 CH (p-Ph2), 128.74 2 × CH (Ph), 130.06 2 × CH (m-Ph1′), 130.22 CH (p-Ph3′), 130.96 CH,
132.76 CH (p-Ph1′), 134.27 2 × C (i-Ph2 or C-9a), 138.37 C (i-Ph3′ or i-Ph1′), 144.22 C (C-3′),
144.32 C (C-1), 145.38 C (C-3a), 192.36 C (C-1′). The mother liquor was subjected to a column
chromatography on silica gel (10 g). The dichloromethane fractions contained pyrrole derivative 20.
1H NMR spectrum: 2.58 s, 3 H (Me-4); 6.64 s, 1 H (H-4′); 7.03–7.15 m, 6 H (Ph); 7.16–7.29 m, 8 H
(H-3 and Ph); 7.54 dd, 1 H, J = 8.0 and 7.0 (H-7); 7.61–7.71 m, 3 H (Ph, H-6); 7.88 d, 1 H, J = 8.0
(H-5); 7.94 d, 1 H, J = 8.0 (H-8). 13C NMR spectrum: 19.40 CH3 (C-4), 112.80 CH (C-4′), 122.00 CH
(C-3), 124.36 CH, 127.25 CH, 127.36 CH, 127.96 (C-4a), 128.21 2 × CH, 128.35 CH, 128.52 2 × CH,
128.89 2 × CH, 129.58 2 × CH, 130.03 2 × CH, 130.31 CH, 130.51 2 × CH, 131.08 C, 132.44 C,
132.51 CH (p-Ph2), 133.79 C, 135.79 C (i-Ph), 139.17 C (i-Ph), 139.29 C (i-Ph), 146.98 C (C-4),
147.44 C (C-8a), 151.47 C (C-2), 188.89 C (CO). The elution with the dichloromethane–diethyl ether
(9 : 1) solvent gave the second portion of the isomeric ketone 3. Total yields and other characteristics
of compounds 3 and 20 are given in Table III.
(Z)-1,3-Diphenyl-3-(2-phenylbenzo[h]imidazo[1,2-a]quinolin-1-yl)prop-2-en-1-one (4)
and [1-(Benzo[h]quinolin-2-yl)-3,5-diphenyl-1H-pyrrol-2-yl]phenylmethanone (17)
The reaction of perchlorate 14 (1 g, 1.71 mmol) in ethanol (45 ml) with potassium ferricyanide (1.69 g,
5.13 mmol) and potassium hydroxide (0.44 g, 7.96 mmol) in water (9 ml) was carried out in the
same way as above mentioned but the products were extracted with 3 × 50 ml chloroform. Crystal-
lization of the crude mixture from ethanol and heptane–toluene (1 : 1) afforded the major amount of
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1607
pyrrole derivative 17. 1H NMR spectrum: 6.74 s, 1 H (H-4′); 7.10–7.33 m, 12 H (H-3 and Ph); 7.42–7.47 m,
2 H (Ph); 7.49 ddd, 1 H, J = 8.0, 8.0 and 1.0 (H-9); 7.59 d, 1 H, J = 9.0 (H-6); 7.63 ddd, 1 H, J = 7.5,
8.0 and 1.0 (H-8); 7.77 d, 1 H, J = 9.0 (H-5); 7.79 d, 2 H, J ≈ 8.5 (Ph); 7.85 d, 1 H, J = 8.0 (H-7); 7.98 d,
1 H, J = 8.5 (H-4); 8.67 d, 1 H, J = 8.0 (H-10). 13C NMR spectrum: 112.72 CH (C-4′), 120.78 CH
(C-3), 125.22 CH, 125.44 CH, 125.50 C (C-4a), 127.31 CH, 127.58 CH, 128.16 CH, 128.33 CH,
128.43 2 × CH, 128.58 CH, 128.70 2 × CH, 128.94 3 × CH, 129.66 2 × CH, 129.78 2 × CH, 130.29
2 × CH, 130.99 C, 131.63 C, 131.97 C, 132.71 C, 132.77 CH (p-Ph2), 134.38 C, 135.43 C, 137.84 C,
137.91 CH (C-4), 139.21 C, 145.91 C (C-10b), 149.83 C (C-2), 190.18 C (CO). The mixture ob-
tained from collected mother liquors was chromatographed on a silica gel column (15 g, 80/25 µm,
8% H2O, chloroform–diethyl ether 9 : 1). In addition to a smaller portion of pyrrole 17, the following
coloured fractions contained a red light-sensitive substance identified as ketone 4. 1H NMR spec-
trum: 6.56 d, 2 H, J = 7.5 (Ph); 6.83 dd, 2 H, J = 8.0 and 7.5 (Ph); 6.90–7.01 m, 3 H (H-2′ and Ph);
7.07 dd, 2 H, J = 7.5 and 7.5 (Ph); 7.27 dd, 2 H, J = 7.5 and 7.5 (Ph); 7.36 ddd, 1 H, J = 7.5, 7.5
and 1.5 (H-9); 7.40–7.57 m, 8 H (H-5, H-8. H-10 and Ph); 7.60 d, 1 H, J = 9.0 (H-4); 7.67 d, 1 H,
J = 8.0 (H-7); 7.79 d, 1 H, J = 9.0 (H-6); 9.02 d, 1 H, J = 8.5 (H-11). 13C NMR spectrum: 117.36 CH
(C-4), 123.02 CH, 124.90 C, 124.97 CH, 125.06 C, 125.40 CH, 126.10 (C-5), 126.21 CH, 127.44 2 × CH
(o-Ph), 127.61 CH (p-Ph2), 127.95 CH (C-2′), 128.01 2 × CH (Ph), 128.56 2 × CH (Ph), 128.62 2 × CH
(Ph), 128.70 4 × CH, 129.67 2 × CH (m-Ph1′), 129.80 CH (p-Ph3′), 131.13 C, 133.05 CH (p-Ph1′),
133.35 C, 135.46 C (i-Ph2), 138.31 and 138.38 (i-Ph1′ and i-Ph3′), 145.26 C (C-3′), 148.00 C (C-1),
148.16 C (C-3a), 190.91 C (C-1′). Total yields and other characteristics of compounds 4 and 17 are
given in Table III.
(Z)-3-(5-Methyl-2-phenylbenzo[h]imidazo[1,2-a]quinolin-1-yl)-1,3-diphenylprop-2-en-1-one (5)
and [1-(4-Methylbenzo[h]quinolin-2-yl)-3,5-diphenyl-1H-pyrrol-2-yl]phenylmethanone (18)
Reaction of perchlorate 15 (0.5 g, 0.84 mmol) in ethanol (25 ml) with potassium ferricyanide (0.81 g,
2.46 mmol) and potassium hydroxide (0.24 g, 4.28 mmol) in water (3 ml) was carried out by the
standard procedure using 100 g of ice and extraction with 3 × 25 ml chloroform. The crude reaction
mixture (0.47 g) was chromatographed on a silica gel column (10 g, 80/25 µm, 8% H2O). Yellow
chloroform fractions contained pyrrole derivative 18 which was recrystallized from ethanol–toluene
1
(5 : 2). H NMR spectrum: 2.55 s, 3 H (Me-4); 6.69 s, 1 H (H-4′); 7.02 s, 1 H (H-3); 7.08–7.30 m,
11 H (Ph); 7.38 dd, 2 H, J = 8.0 and 1.5 (Ph); 7.44 dd, 1 H, J = 8.5 and 7.0 (H-9); 7.60 dd, 1 H, J =
8.5 and 7.0 (H-8); 7.76 dd, 2 H, J = 8.0 and 1.5 (H-5 and H-6); 7.79 s, 2 H (Ph); 7.84 d, 1 H, J =
7.5 (H-7); 8.64 d, 1 H, J = 8.0 (H-10). 13C NMR spectrum: 19.64 CH3 (Me-4), 112.60 CH (C-4′),
121.51 CH, 121.75 CH, 125.27 C (C-4a), 125.97 CH, 127.29 CH, 127.54 CH, 128.03 CH, 128.22 CH,
128.29 CH, 128.41 2 × CH, 128.71 2 × CH, 128.77 CH, 128.87 2 × CH, 129.74 2 × CH, 129.84 2
× CH, 130.42 2 × CH, 131.15 C, 131.97 C, 132.20 C, 132.97 C, 134.25 C, 135.67 C, 138.06 C,
139.45 C, 145.78 C (C-10b), 146.56 C (C-4), 149.68 C (C-2′), 190.20 C (CO). The following red
eluates (chloroform–diethyl ether 95 : 5) contained a light-sensitive substance identified as ketone 5
1
which was recrystallized from ethanol–heptane (4 : 1). H NMR spectrum: 2.67 s, 3 H (Me-5); 6.52 d,
2 H, J = 7.5 (Ph); 6.81 dd, 2 H, J = 8.0 and 7.5 (Ph); 6.89–7.00 m, 3 H (H-2′ and Ph); 7.06 dd, 2 H, J
= 7.5 and 7.5 (Ph); 7.27 dd, 2 H, J = 7.5 and 7.5 (Ph); 7.35 dd, 1 H, J = 7.5 and 7.5 (H-9); 7.40–7.60
m, 7 H (H-8, H-10 and Ph); 7.62 s, 1 H (H-4); 7.66 d, 1 H, J = 7.5 (H-7); 7.68 d, 1 H, J = 9.0 (H-6);
9.04 d, 1 H, J = 9.0 (H-11). 13C NMR spectrum: 116.97 CH (C-4), 121.80 CH, 122.73 CH, 123.05 C,
124.43 C, 125.00 CH, 125.05 C, 125.81 CH, 126.29 CH, 127.19 2 × CH (o-Ph), 127.42 CH (p-Ph2),
127.81 CH (C-2′), 127.97 2 × CH (o-Ph), 128.51 2 × CH (Ph), 128.66 2 × CH (Ph), 128.69 2 × CH
(Ph), 129.62 2 × CH (m-Ph1′), 131.03 C, 132.97 CH (p-Ph1′), 133.03 C, 134.68 C (C-5), 138.39 C
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

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Bohm, Strnad, Ruppertova, Kuthan:
(i-Ph1′), 138.48 C (i-Ph3′), 145.41 C (C-3′), 147.74 C (C-1), 147.89 C (C-3a), 190.91 C (C-1′).
Yields and other characteristics of compounds 5 and 18 are given in Table III.
(Z)-1,3-Diphenyl-3-(2-phenylimidazo[1,2-a]-1,10-phenanthrolin-1-yl)prop-2-en-1-one* (6)
and [1-(1,10-Phenanthrolin-2-yl)-3,5-diphenyl-1H-pyrrol-2-yl]phenylmethanone (19)
Method A. The reaction of perchlorate 16 (0.1 g, 0.166 mmol) in ethanol (7 ml) with potassiumn
ferricyanide (0.11 g, 0.334 mmol) and potassium hydroxide (50 mg, 0.85 mmol) in water (1 ml) was
carried out by the standard procedure, using ice (50 g) and extraction with chloroform. The prep-
arative separation of products was performed by TLC on a loose silica gel layer (20 g, <80 µm,
deactivated with 6% aqueous NH3) using dichloromethane–toluene–1% ethanolic ammonia (15 : 15 : 2.2) as
an eluent. A more mobile yellow zone was extracted with dichloromethane–methanol (1 : 1) and af-
1
forded pyrrole derivative 19 which was crystallized from heptane–toluene (3 : 1). H NMR spectrum:
6.62 s, 1 H (H-4′); 6.99–7.13 m, 5 H (Ph); 7.15–7.24 m, 6 H (Ph); 7.28–7.33 m, 2 H (Ph); 7.42 d, 1 H, J =
8.0 (H-3); 7.51 dd, 1 H, J = 8.0 and 4.5 (H-8); 7.69 dd, 2 H, J = 7.5 and 1.5 (H-5 and H-6); 7.75 s,
2 H (Ph); 8.15 d, 2 H, J ≈ 8.0 (H-4 and H-7); 8.98 dd, 1 H, J = 4.5 and 1.5 (H-9). 13C NMR spec-
trum: 112.72 CH (C-4′), 123.54 CH (C-5), 126.54 CH, 123.64 CH (C-6), 127.15 CH, 127.65 CH,
128.06 2 × CH, 128.32 CH, 128.37 C, 128.41 2 × CH, 128.87 2 × CH, 129.58 C, 129.85 2 × CH,
130.14 2 × CH, 130.63 2 × CH, 131.40 C, 132.26 CH (p-PhCO2′), 132.36 C, 134.16 C, 135.95 C,
136.33 CH (C-4), 138.28 CH (C-7), 139.25 C, 139.59 C, 145.98 C (C-10a), 146.45 (C-10b), 150.80 CH
(C-9), 152.07 C (C-2), 188.81 C (CO). A less mobile orange zone was repeatedly chromatographed
until no traces of minor component 19 were detected in extracts. After the procedure only ketone 6
was present in the extract; it was recrystallized from ethanol–heptane (1 : 2). 1H NMR spectrum:
6.85 s, 1 H (H-2′); 7.04 dd, 2 H, J = 8.0 and 7.5 (Ph); 7.09–7. 28 m, 9 H (Ph); 7.31 dd, 1 H, J = 8.0
and 4.0 (H-9); 7.56–7.65 m, 4 H (H-4, H-5 and Ph); 7.71–7.81 m, 4 H (H-6, H-7 and Ph); 8.06 dd,
1 H, J = 8.0 and 1.5 (H-8); 8.25 dd, 1 H, J = 4.0 and 1.5 (H-10). 13C NMR spectrum: 119.25 CH
(C-4), 122.07 CH (C-7), 122.19 CH (C-6), 124.92 CH, 125.39 C, 125.94 C, 126.37 CH (C-5), 127.46 CH,
127.73 CH, 127.79 2 × CH (Ph), 127.87 C, 128.12 2 × CH (Ph), 128.17 2 × CH (Ph), 128.52 2 × CH,
129.61 4 CH (Ph), 130.92 C, 132.23 (p-Ph1′), 135.18 C (i-Ph2), 135.57 CH (C-8), 138.71 and 139.03
(i-Ph1′ and i-Ph3′), 140.48 C, 145.54 CH (C-10), 146.60 C (C-3′), 146.87 C (C-1), 148.19 C (C-3a),
191.41 C (C-1′). Other characteristics of the products are given in Table III, yields are shown in
Table II.
Method B. A solution of potassium ferricyanide (0.11 g, 0.334 mmol) and potassium hydroxide
(50 mg, 0.85 mmol) in water (1.5 ml) was added to an ice-cold solution of perchlorate 16 (0.1 g,
0.166 mmol) and the mixture was stirred for 1.5 h under argon. The isolation of products 6 and 19
was accomplished in the same way as above (see Table II).
Heterocyclic Amines 7–11
Isoquinolin-1-ylamine (7) was a commercial product (Aldrich), 4-methylquinolin-2-ylamine (8) and
benzo[h]quinolin-2-ylamine (9) were prepared by the described10,11 procedures. An analogous Tschits-
chibabin reaction was used for the preparation of 4-methylbenzo[h]quinolin-2-ylamine (10): A mix-
* For numbering compatibility of compounds 4–6, needed for correlation of NMR signals, incorrect name of
6 was used. Correct IUPAC name is (Z)-1,3-diphenyl-3-(10-phenylimidazo[1,2-a]-1,10-phenanthrolin-
11-yl)prop-2-en-1-one.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1609
ture of 4-methylbenzo[h]quinoline12 (4.15 g), sodium amide (5.5 g) and freshly distilled N,N-di-
methylaniline (30 ml) was stirred in a closed apparatus at 125 °C for 24 h. The reaction mixture was
then decomposed with water (100 ml), extracted with chloroform and the combined organic layers
were evaporated to dryness. The residue (4.2 g) was chromatographed on a silica gel column (120 g)
with a toluene–chloroform (6 : 4) mixture saturated with dry ammonia. Amine 10 (2.8 g) was recry-
stallized from heptane–toluene (10 : 1), m.p. 129–131 °C, and used without additional purification
(ref.13 reported m.p. 133–134 °C). 1H NMR spectrum: 2.65 s, 3 H (Me-4); 4.77 bs, 2 H (NH2-2);
6.68 s, 1 H (H-3); 7.58–7.67 m, 3 H (H-6, H-8 and H-9); 7.77 d, 1 H, J = 9.0 (H-5); 7.85 ddd, 1 H,
J = 8.0, ≈ 4.0 and 1.0 (H-7); 9.15 ddd, 1 H, J = 8.0, ≈ 4.0 and 1.0 (H-10). 1,10-Phenanthrolin-2-
ylamine (11) was obtained by the reaction of ammonia and phenol with the 2-chloro derivative14.
1-(Isoquinolin-1-yl)-2,4,6-triphenylpyridinium Perchlorate (12)
A mixture of 2,4,6-triphenylpyrylium perchlorate15 (1 g, 2.6 mmol) and 1-aminoisoquinoline (0.5 g,
3.5 mmol) in ethanol (40 ml) was refluxed for 8 h. The crystals precipitated after cooling were
sucked off, washed with ether and crystallized from ethanol. Yield 1.1 g of perchlorate 12, see Table I.
1H NMR spectrum ((CD3)2SO): 7.15–7.30 m, 6 H (m,p-Ph2 and m,p-Ph6); 7.32–7.37 m, 4 H (o-Ph2′
and o-Ph6′); 7.64–7.79 m, 6 H (H-4, H-5, H-7 and m,p-Ph4′); 7.87–7.95 m, 3 H (H-6 and o-Ph4′);
8.35–8.38 m, 1 H (H-8); 8.43–8.47 m, 1 H (H-3); 8.85 s, 2 H (H-3 and H-5). 13C NMR spectrum
((CD3)2SO): 123 CH, 123.90 C, 124.46 CH, 125.97 CH, 127.09 CH, 127.94 CH, 129.23 CH, 129.38 CH,
129.64 CH, 130.01 CH, 130.45 CH, 131.78 C, 132.01 CH, 132.91 CH, 133.35 C, 136.98 C, 140.02 CH,
149.18 C, 155.62 C, 157.27 C.
1-(4-Methylquinolin-2-yl)-2,4,6-triphenylpyridinium Perchlorate (13)
A solution of amine 8 (4.22 g, 10.36 mmol) in ethanol (10 ml) was added to a boiling solution of
2,4,6-triphenylpyrylium perchlorate15 in ethanol (80 ml). The mixture was refluxed for 8.5 h and then
cooled. The crystals of product 13 contained traces of the starting salt and therefore were purified by
1
crystallization from ethanol and ethanol–nitromethane (10 : 1) (see Table I). H NMR spectrum: 2.50 s,
3 H (Me-4); 7.15–7.24 m, 6 H (m,p-Ph2′ and m,p-Ph6′); 7.18 d, 1 H, J = 8.5 (H-8); 7.54–7.63 m, 9 H
(H-7, m,p-Ph4′, o-Ph2′ and o-Ph6′); 7.65 s, 1 H (H-3); 7.70 ddd, 1 H, J = 7.5, 8.5 and 1.5 (H-6); 7.93 dd,
2 H, J = 8.0 and 2.5 (o-Ph4′); 8.14 s, 2 H (H-3′ and H-5′). 13C NMR spectrum: 19.20 CH3 (Me-4),
122.13 CH (C-3), 124.80 CH (C-6), 127.07 2 × CH (C-3′ and C-5′), 128.30 C (C-4a), 129.00 4 × CH
(m-Pha2′ and m-Ph6′), 129.24 2 × CH (o-Ph4′), 130.00 CH (C-5), 130.43 2 × CH (m-Ph4′), 130.54
4 × CH (o-Ph2′ and o-Ph6′), 130.93 2 × CH (p-Ph2′ and p-Ph6′), 131.33 CH (C-7), 132.81 CH (p-Ph4′),
133.14 2 × C (i-Ph2′ and i-Ph 6′), 135.49 C (i-Ph4′), 145.91 C (C-8a), 149.91 C (C-4), 151.23 C (C-4′),
156.70 2 × C (C-2′ and C-6′), 158.97 C (C-2).
1-(Benzo[h]quinolin-2-yl)-2,4,6-triphenylpyridinium Perchlorate (14)
The reaction of 2,4,6-triphenylpyrylium perchlorate15 (3 g, 7.25 mmol) in ethanol (90 ml) with amine 9
(1.55 g, 7.98 mmol) in ethanol (10 ml) was performed as mentioned above and completed after 7.5 h.
1
Almost quantitative yield of product 14 was obtained (see Table I). H NMR spectrum: 7.10–7.18 m,
6 H (m,p-Ph2′ and m,p-Ph6′), 7.52–7.63 m, 8 H (H-3, o-Ph2′, o-Ph6′ and m,p-Ph4′); 7.72–7.78 m, 2
H (H-8 and H-9); 7.84 d, 2 H, J ≈ 9.0 and ≈ 9.0 (H-4 and H-6); 7.92 dd, 1 H, J = 8.0 and 4.0 (H-7);
7.97 d, 3 H, J = 8.0 (o-Ph4′ and H-5); 8.19 s, 2 H (H-3′ and H-5′); 8.88 dd, 1 H, J = 8.0 and 4.1
(H-10). 13C NMR spectrum: 122.49 CH (H-3), 124.72 CH, 125.14 CH (C-6′), 126.91 C (C-4a),
127.07 2 × CH (C-3′ and C-5′), 128.31 CH, 128.75 CH, 129.00 4 × CH (m-Ph2′ and m-Ph6′), 129.25
2 × CH (o-Ph4′), 129.85 CH (C-7), 130.41 2 × CH (m-Ph4′), 130.48 4 × CH (o-Ph2′ and o-Ph6′),
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1610
Bohm, Strnad, Ruppertova, Kuthan:
130.60 CH, 130.88 2 × CH (p-Ph2′ and p-Ph6′), 131.01 C (C-10a), 132.81 CH (p-Ph4′), 133.22 2 × C
(i-Ph2′ and i-Ph6′), 134.56 C (C-6a), 135.43 C (i-Ph4′), 139.56 CH (C-4), 145.00 C (C-10b), 150.18 C
(C-4′), 156.86 2 C (C-2′ and C-6′), 159.00 C (C-2).
1-(4-Methylbenzo[h]quinolin-2-yl)-2,4,6-triphenylpyridinium Perchlorate (15)
The reaction of 2,4,6-triphenylpyrylium perchlorate15 (3.3 g, 8.07 mmol) and amine 10 (1.85 g, 8.88 mmol)
in ethanol (100 ml) was performed by the standard procedure for 9 h. The precipitated salt 15 was
1
washed with ethanol and recrystallized from ethanol–nitromethane (1 : 20) (see Table I). H NMR
spectrum: 2.50 s, 3 H (Me-4); 7.10–7.22 m, 6 H (m,p-Ph2′ and m,p-Ph6′); 7.54–7.64 m, 7 H (o-Ph2′,
o-Ph6′ and m,p-Ph4′); 7.68–7.77 m, 4 H (H-3, H-6, H-8 and H-9); 7.85 d, 1 H, J = 9.0 (H-5); 7.91 dd,
1 H, J = 8.0 and 4.0 (H-7); 7.96 dd, 2 H, J = 7.9 and 2.2 (o-Ph4′); 8.17 s, 2 H (H-3′ and H-5′); 8.91 dd,
1 H, J = 8.0 and 4.0 (H-10). 13C NMR spectrum: 19.55 CH3 (Me-4), 121.42 CH (C-3), 122.95 CH,
125.08 CH, 126.46 C (C-4a), 127.00 2 × CH (C-3′ and C-5′), 128.23 CH, 128.59 CH, 128.94 4 × CH
(m-Ph2′ and m-Ph6′), 129.22 2 × CH (o-Ph4′), 129.60 CH, 130.11 CH, 130.39 2 × CH (m-Ph4′),
130.46 4 × CH (o-Ph2′ and o-Ph6′), 131.47 C (C-10a), 132.79 CH (p-Ph4′), 133.29 2 × C (i-Ph2′ and
i-Ph6′), 134.31 C (C-6a), 135.41 C (i-Ph4′), 144.57 C (C-10b), 149.27 C (C-4), 149.87 C (C-4′),
156.85 2 × C (C-2′ and C-6′), 158.80 C (C-2).
1-(1,10-Phenanthrolin-2-yl)-2,4,6-triphenylpyridinium Perchlorate (16)
The reaction of 2,4,6-triphenylpyrylium perchlorate15 (1.33 g, 3.26 mmol) and amine 11 (0.7 g, 3.586 mmol)
in boiling ethanol (40 ml) was carried out by the standard procedure. After 8 h the hot reaction mix-
ture was treated with charcoal, filtered and, after addition of twenty drops of 70% HClO4, cooled.
The originally separated oily product solidified and was recrystallized from ethanol–nitromethane (4 : 1)
1
(see Table I). H NMR spectrum: 7.09–7.18 m, 6 H (m,p-Ph2′ and m,p-Ph6′); 7.56–7.67 m, 7 H (o-Ph2′,
o-Ph6′ and m,p-Ph4′); 7.69 d, 1 H, J = 9.0 (H-5); 7.71 dd, 1 H, J = 8.0 and 4.5 (H-8); 7.86 d, 1 H, J =
9.0 (H-6); 7.92 dd, 2 H, J = 7.5 and 2.5 (o-Ph4′); 8.01 d, 1 H, J = 8.5 (H-3); 8.09 d, 1 H, J = 8.5
(H-4); 8.16 s, 2 H (H-3′ and H-5′); 8.29 dd, 1 H, J = 8.0 and 1.5 (H-7); 9.20 dd, 1 H, J = 4.5 and
1.5 (H-9). 13C NMR spectrum: 124.25 CH, 124.55 CH, 126.49 CH, 127.31 2 × CH (C-3′ and C-5′),
129.00 4 CH (m-Ph2′ and m-Ph6′), 129.24 2 × CH (o-Ph4′), 129.41 C, 129.55 CH, 130.10 C, 130.45
2 × CH (m-Ph4′), 130.91 6 × CH (o,p-Ph2′ and o,p-Ph6′), 132.76 CH (p-Ph4′), 133.13 2 × C (i-Ph2′
and i-Ph6′), 135.68 C (i-Ph4), 137.03 CH (C-7), 140.19 CH (C-4), 144.74 C (C-10a), 145.85 C (C-10b),
151.47 CH (C-9), 151.54 C (C-4′), 157.05 2 × C (C-2′ and C-6′), 159.28 C (C-2).
Calculations
Various MO models of molecules of 4 and 6 were calculated by the semiempirical PM3 method16 for
given torsion angles Φ (Figs 1 and 2) using a full optimization procedure with respect to all other
geometric degrees of freedom including the torsion angle Ψ (formulae 22 and 23). The data for con-
formers 4a–4d and 6a–6d are collected in Table V.
This work was supported by the Grant Agency of the Czech Republic (project No. 203/93/0320). The
authors are indebted to the staff of Central Laboratories (Prague Institute of Chemical Technology) for
elemental analyses.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Sterically Crowded Heterocycles
1611
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