One-pot site-selective Sonogashira cross-coupling-heteroannulation of the 2-aryl-6,8-dibromoquinolin-4(1H)-ones: Synthesis of novel 6-H-pyrrolo[3,2,1-ij]quinolin-6-ones

Article abstract of DOI:10.3184/174751914X14097554893763

The 2-aryl-6,8-dibromoquinolin-4(1H)-ones were subjected to site-selective Sonogashira cross-coupling with terminal acetylenes as models for Csp²-Csp bond formation in the presence of Pd/C-PPh₃and CuI as catalysts and K₂CO₃as a base in dioxane to afford the 2-substituted 4-aryl-8-bromo-4H-pyrrolo[3,2,1-ij ]quinolin-6-ones. These were, in turn, subjected to Suzuki-Miyaura cross-coupling with 4-fluorophenylboronic acid as coupling partner to afford the 2-substituted 4,8-diaryl-4H-pyrrolo[3,2,1-ij ]quinolin-6-ones.

Full text of DOI:10.3184/174751914X14097554893763

JOURNAL OF CHEMICAL RESEARCH 2014
VOL. 38 SEPTEMBER, 535–538
RESEARCH PAPER 535
One-pot site-selective Sonogashira cross-coupling–heteroannulation
of the 2-aryl-6,8-dibromoquinolin-4(1H)-ones: synthesis of novel
6-H-pyrrolo[3,2,1-ij]quinolin-6-ones
Malose J. Mphahlele* and Felix A. Oyeyiola
Department of Chemistry, College of Science, Engineering and Technology, University of South Africa, PO Box 392, Pretoria 0003, South Africa
The 2‑aryl‑6,8‑dibromoquinolin‑4(1H)‑ones were subjected to site‑selective Sonogashira cross‑coupling with terminal
acetylenes as models for Csp2–Csp bond formation in the presence of Pd/C–PPh3 and CuI as catalysts and K2CO3 as a base
in dioxane to afford the 2‑substituted 4‑aryl‑8‑bromo‑4H‑pyrrolo[3,2,1‑ij]quinolin‑6‑ones. These were, in turn, subjected to
Suzuki–Miyaura cross‑coupling with 4‑fluorophenylboronic acid as coupling partner to afford the 2‑substituted 4,8‑diaryl‑4H‑
pyrrolo[3,2,1‑ij]quinolin‑6‑ones.
Keywords: 2‑aryl‑6,8‑dibromoquinolin‑4(1H)‑ones, Sonogashira cross‑coupling; 2,4‑diaryl‑8‑bromo‑4H‑pyrrolo[3,2,1‑ij]
quinolin‑6‑ones, Suzuki–Miyaura cross‑coupling, 2,4,8‑triaryl‑6H‑pyrrolo[3,2,1‑ij]quinolin‑6‑ones
The 5,6‑dihydro‑4H‑pyrrolo[3,2‑ij]quinoline ring occurs
in numerous natural products and this moiety constitutes
the central core of different series of compounds
exerting platelet activating factor production inhibition.1
Pyrrolo[3,2.1‑ij]quinoline derivatives have also shown
potent histamine and platelet activating factor antagonism
and 5‑lipoxygenase inhibitory properties.2 Moreover, some
pyrrolo[3,2‑ij]quinolines exhibit antibacterial and antifungal
activities for diseases of rice plants.3 The preparation of
the 6‑oxopyrroloquinolines has generally been based on
the cyclodehydration of a suitably functionalised indole
derivative.4 Recently, a great deal of work has been focused
on the synthesis of these compounds from halogenated
quinolinones and quinoline derivatives by transition metal
catalysed cross‑coupling with terminal alkynes. This strategy
takes advantage of the ease of displacement of the halogen
atom/s on the aryl or heteroaryl moiety by metal to facilitate
carbon–carbon bond formation and the proximity of the
tethered nucleophilic heteroatom to promote heteroannulation.
Palladium‑mediated cross‑coupling of the 8‑iodoquinolin‑
4(1H)‑one derivatives with propargyl alcohols, for example,
previously afforded the 6‑oxopyrroloquinolines in a single‑
pot operation albeit in low to moderate yields (8–68%).5 A
similar approach was later adapted for the synthesis of N‑(4‑
chlorobenzyl)‑2‑(2‑hydroxyethyl)‑8‑(morpholin‑4‑ylmethyl)‑
respectively) and to a lesser extend the electronic effect of its
position on the heterocycle.9 However, for quinolinones bearing
multiple identical halogen atoms particularly on the fused
benzo ring, the bond strengths are very similar10 and this makes
it difficult to predict easily the selectivity of cross‑coupling.
Our interest in the synthesis of polysubstituted and
heteroannulated quinolinones prompted us to investigate
the reactivity of the 2‑aryl‑6,8‑dibromoquinolin‑4(1H)‑one
derivatives in Sonogashira cross‑coupling with phenylacetylene
as coupling partner. We envisage that the increased acidity of
NH and the proximity of the 8‑alkynyl group to nitrogen of the
incipient 8‑alkynyl‑2‑arylquinolin‑4(1H)‑ones would facilitate
direct one‑pot metal‑mediated heteroannulation to afford novel
4H‑pyrrolo[3,2,1‑ij]quinolin‑6‑ones with potential to undergo
further transformation.
The 2‑aryl‑6,8‑dibromoquinolin‑4(1H)‑ones required as
substrates in this investigation were previously isolated in trace
amounts along with the corresponding 2‑aryl‑6,8‑dibromo‑4‑
methoxyquinolines (major) from the oxidative‑cyclisation of
the corresponding 2‑aminochalcones with iodine in methanol
under reflux.11 Hitherto, 6,8‑dibromo‑2‑phenylquinolin‑4(1H)‑
one was isolated as a minor product from the reaction of
2‑phenyl‑2,3‑dihydroquinolin‑4(1H)‑one with excess bromine
(4 equiv.) in chloroform.12 Our first task in this investigation
was to synthesise the requisite 2‑aryl‑6,8‑dibromoquinolin‑
4(1H)‑ones in reasonable quantities to serve as substrates for
the palladium‑catalysed Sonogashira cross‑coupling with
terminal alkynes. We opted for the use of the known 2‑aryl‑6,8‑
dibromo‑2,3‑dihydroquinolin‑4(1H)‑ones 1a–d13 as precursors
because of the potential of their heterocyclic ring to undergo
different degrees of unsaturation by dehydrogenation or
oxidative aromatisation. One approach for the dehydrogenation
of the 2‑aryl‑2,3‑dihydroquinolin‑4(1H)‑ones makes use of
iodobenzene diacetate under basic conditions in methanol14
and the other employs thallium(III) p‑tolylsulfonate in
dimethoxyethane to afford the 2‑arylquinolin‑4‑(1H)‑ones.15
We opted for the use of the readily prepared and easy‑to‑handle
thallium(III) p‑tolylsulfonate (TTS) in dimethoxyethane
(DME) and subjected compounds 1a–d to dehydrogenation
to afford the corresponding potentially tautomeric 2‑aryl‑
6,8‑dibromoquinolin‑4(1H)‑ones 2a–d in reasonable yields
and high purity without the need for column chromatographic
purification (Scheme 1). The analogous 6,8‑dibromoflavone
has been found to undergo the Heck reaction with methyl
acrylate to afford mixtures of both 6‑ and 8‑monosubstituted
and 6,8‑disubstituted flavones.16
6‑oxo‑6H‑pyrrolo[3,2,1‑ij]quinolin‑5‑carboxamide
(PHA‑
529311), which exhibits improved activity against herpes virus
DNA polymerase.6 Layek et al.7 also reported a high yielding
single‑step synthesis of the 2‑substituted 5‑carbethoxy‑6H‑
pyrrolo[3,2,1‑ij]quinolin‑6‑ones by cross‑coupling of 8‑iodo‑
4‑oxo‑1,4‑dihydroquinoline‑3‑carboxylic acid ethyl esters
with a variety of terminal alkynes using Pd/C–PPh3–CuI pre‑
catalyst mixture in ethanol. This catalyst mixture has also been
found to promote regioselective C‑8 alkynylation of 6‑bromo‑
8‑iodoquinolines7 or in situ cross‑coupling–heteroannulation
of 8‑iodo‑4‑oxo‑1,4‑dihydroquinoline‑3‑carboxylic acid ethyl
esters8 and 6‑(chloro/methyl)‑8‑iodo‑2,3‑dihydroquinolin‑
4(1H)‑ones4 to afford the 2‑substituted 6‑oxopyrrolo‑
[3,2,1‑ij]‑quinolines and 4H‑pyrrolo[3,2,1‑ij]quinolin‑6‑ones,
respectively. The selectivity in the case of the less readily
accessible chloroiodo‑ and bromoiodoquinolinones has been
found to depend largely on the intrinsic reactivity of the halide
to be displaced (trend: I>Br>Cl>>F),4,7 which relates to the
Ar–X bond strength (DPh–X values 65, 81, 96, and 126 kcal mol–1,
* Correspondent. E‑mail: m.p.hahmj@unisa.ac.za

536 JOURNAL OF CHEMICAL RESEARCH 2014
O
O
Br
Br
(i)
N
C6H4R
N
H
C6H4R
Br
H
Br
1a–d
2a–d
4‑R
% Yield of 2
2a
2b
2c
2d
4‑H
86
80
88
82
4‑F
4‑Cl
4‑OMe
Reagents and conditions: (i) TTS, DME, 100 °C, 30 minutes.
Scheme 1 Thallium(III) p‑tolylsulfonate (TTS)‑promoted dehydrogenation of 1a–d.
Although the 2‑aryl‑6,8‑dibromo‑2,3‑dihydroquinolin‑
dxy (HOMO) in the oxidative‑addition stage.10 We rationalise
the formation of compounds 3a–d to be the result of the initial
site‑selective Pd‑mediated Csp2–Csp bond formation and
subsequent intramolecular attack of the nucleophilic nitrogen
atom on the metal‑activated triple bond of B. The observed site
selectivity of Csp2–Csp bond formation through C‑8 (versus
C‑6) is attributed to the ortho directing effect of NH in analogy
with literature precedence for the dihalogenated benzo‑fused
heterocycles having two similar halogen groups.17 Moreover,
preferential oxidative‑addition of the Pd(0) catalyst ortho to
the N–H bond would result in the formation of complex A in
which the C‑8 position is activated by coordination of the N–H
bond electron density with palladium. The oxidative addition
of the arylhalide (X=Br, I) has been found to be the main
cause for Pd‑leaching and the process is very slow in organic
solvents.18 However, once generated the organo‑palladium(II)
species is envisioned to undergo facile transmetallation with
copper acetylide followed by reductive elimination with
concomitant redeposition of Pd onto the support (charcoal).18,19
It was previously concluded that the initial slow leaching
from and final redeposition of Pd onto the support inhibit the
heterogenous catalyst, Pd/C, from participating further in the
second cross‑coupling step.19
4(1H)‑ones1a–dundergoSuzuki–Miyauracross‑couplingwith
arylboronic acids without selectivity to afford the 2,6,8‑triaryl‑
2,3‑dihydroquinolin‑4(1H)‑ones,13 the analogous 6‑bromo‑
8‑iodoquinolines were found to undergo regioselective C‑8
alkynylation with excess terminal acetylenes (3 equiv.) using
Pd/C–PPh3–CuI pre‑catalyst mixture.7 We envisage that this
catalyst mixture could also affect site‑selective Sonogashira
cross‑coupling of compounds 2a–d with minimum or no effect
on the 6‑bromo atom. Based on this hypothesis, we subjected
compound 2a to phenylacetylene (2.5 equiv.) in the presence
of Pd/C–PPh3–CuI catalyst complex and triethylamine as a
base in N,N‑dimethyl formamide–water mixture (4:1, v/v)
at 110 °C as an exploration based on literature precedent. We
isolated albeit in low yield (<30%) product 3a formed by in
situ monoalkynylation and subsequent heteroannulation. After
some experimentation we found the use of Pd/C–PPh3–CuI
mixture and K2CO3 as a base in dioxane to lead to improved
yields of the 8‑bromo‑2,4‑diphenyl‑4H‑pyrrolo[3,2,1‑ij]
quinolin‑6‑one 3a. These reaction conditions were extended
to other derivatives 2 using phenylacetylene to afford products
3a–d (Scheme 2). Selectivity of the Pd‑catalysed cross‑coupling
reactions of heterocycles bearing multiple identical halogens
with similar C–X bond strengths has been found to depend
largely on the interaction of the heterocycle π* (LUMO)–PdL2
To demonstrate the potential of the 8‑bromo‑2,4‑diaryl‑4H‑
pyrrolo[3,2,1‑ij]quinolin‑6‑ones 3 in synthesis, we subjected
O
O
Br
O
O
Br
Br
Br
i
( )
N
H
C6H4R
B
C6H4R
N
H
N
C6H4R
N
H
C6H4R
Cu
Pd
Br
Br
C6H5
H
C6
5
2a–d
A
B
3a–d
R
% Yield of 3
3a
4‑H
68
68
65
62
3b
3c
3d
4‑F
4‑Cl
4‑OMe
Reagents and conditions: (i) Ph–C≡CH (3.0 equiv.), 10% Pd/C–CuI, PPh3, K2CO3, DMF–water (3:1, v/v), 110 °C, 18 h.
Scheme 2 One‑pot site‑selective Pd catalysed Sonogashira cross‑coupling and heteroannulation.

JOURNAL OF CHEMICAL RESEARCH 2014 537
O
F
O
Br
(i)
N
C6H4R
N
C6H4R
C6H5
C6H5
3a–d
4a–d
R
% Yield of 4
4a
4b
4c
4d
4‑H
69
57
62
63
4‑F
4‑Cl
4‑OMe
Reagents: (i) 4‑FC6H4B(OH)2, PdCl2(PPh3)2, PCy3, K2CO3, dioxane‑water, 90 °C, 6 h.
Scheme 3 Suzuki–Miyaura cross‑coupling of 3a–d with 4‑fluorophenylboronic acid.
Typical procedure for the site‑selective Sonagashira cross‑coupling of
2a–d
compounds 3a–d to dichlorobis(triphenylphosphine)palladium
(II)‑tricyclohexylphosphine [PdCl2(PPh3)2–PCy3] catalysed
Suzuki–Miyaura cross‑coupling with 4‑fluorophenylboronic
acid in the presence of K2CO3 in dioxane‑water (4:1, v/v). We
isolated the corresponding cross‑coupled products 4a–d in
reasonable yields (Scheme 3).
In summary, the results described herein confirm that the
proximity of the C–X bond to the nucleophilic heteroatom
influence the selectivity of the Csp2–Csp bond formation
during Sonogashira cross‑coupling of quinolinones bearing
two identical halogen atoms on the fused benzo ring.
Hitherto, site‑selectivity of the dihalogenoquinolin‑4‑ones
and their tetrahydroquinoline derivatives was always achieved
through relatively less synthetically accessible chloroiodo‑ or
bromoiodoquinolinone derivatives.
8‑Bromo‑2,4‑diphenyl‑4H‑pyrrolo[3,2,1‑ij]quinolin‑6‑one (3a):
A
mixture of 2a (0.50 g, 1.32 mmol), 10% Pd/C (0.016 g, 0.0132 mmol),
PPh3 (0.014 g, 0.0132 mmol), CuI (0.025 g, 0.13 mmol) and NEt3
(0.33 g, 3.3 mmol) in dioxane (25 mL) in a three‑necked flask
equipped with a stirrer, condenser and a rubber septum was flushed
with nitrogen for 30 min. Phenylacetylene (0.26 g, 2.64 mmol) was
added to the flask using a syringe and the mixture was flushed for an
additional 10 min. The mixture was heated at 110 °C for 5 h under a
nitrogen atmosphere and then allowed to cool. The cooled mixture
was added to a beaker containing an ice‑cold water and the product
was extracted into chloroform. The combined organic layers were
dried over anhydrous MgSO4, filtered, and evaporated under reduced
pressure. The residue was purified by column chromatography on
silica gel using ethyl acetate–hexane mixture as eluant to afford 3a as
a yellow solid (0.177 g, 68%), m.p. 267–269 °C (EtOH); Rf (20% ethyl
acetate–hexane) 0.37; νmax (ATR) 692, 756, 841, 875, 996, 1267, 1456,
1635 cm–1; δH (300 MHz, CDCl3) 6.29 (s, 1H), 6.74 (s, 1H), 6.95–7.08
(m, 9H), 7.18 (t, J=7.5 Hz, 1H), 8.03 (d, J=1.5 Hz, 1H), 8.33 (d,
J=1.5 Hz, 1H); δC (75 MHz, CDCl3) 110.8, 118.2, 118.6, 123.4, 124.9,
127.8, 128.0, 128.3, 128.9, 129.5, 130.3, 130.7, 131.0, 131.3, 135.4, 135.7,
143.2, 148.7, 178.8; m/z 400 (100, MH+); HRMS (ES): MH+, found
400.0339. C23H15NO79Br+ requires 400.0337.
Experimental
Melting points were recorded on a Thermocouple digital melting point
apparatus and are uncorrected. IR spectra were recorded as powders
using a Bruker VERTEX 70 FT‑IR spectrometer with a diamond ATR
(attenuated total reflectance) accessory by using the thin‑film method.
For column chromatography, Merck kieselgel 60 (0.063–0.200 mm)
was used as stationary phase. NMR spectra were obtained from CDCl3
solutions using a Varian Mercury 300 MHz NMR spectrometer and
the chemical shifts are referenced to the solvent peaks. Low‑ and high‑
resolution mass spectra were recorded at an ionisation potential of
8‑Bromo‑4‑(4‑fluorophenyl)‑2‑phenyl‑4H‑pyrrolo[3,2,1‑ij]
quinolin‑6‑one (3b): Yield (0.179 g, 68%), m.p. 279–281 °C (EtOH); Rf
(20% ethyl acetate–hexane) 0.48; νmax (ATR) 761, 839, 997, 1159, 1225,
1459, 1505, 1610, 1637 cm–1; δH (300 MHz, CDCl3) 6.28 (s, 1H), 6.69
(t, J=8.7 Hz, 2H), 6.73 (s, 1H), 6.99–7.15 (m, 7H), 8.03 (d, J=1.8 Hz,
1H), 8.32 (d, J=1.8 Hz, 1H); δC (75 MHz, CDCl3) 110.8, 114.9 (d,
2JCF =21.9 Hz), 118.3, 118.8, 123.4, 124.8, 127.8, 128.3, 128.9, 129.0 (d,
70 eV using
a Synapt G2 Quadrupole time‑of‑flight mass
spectrometer. The synthesis and characterisation of substrates 1 have
been described elsewhere.13 Thallium(III) tolylsulfonate (TTS) was
prepared from thallium(III) nitrate trihydrate and p‑toluenesulfonic
acid following a literature procedure.15
3
4JCF =3.7 Hz), 129.4, 130.6, 131.0 (d, JCF =8.5 Hz), 131.7, 135.4, 143.2,
2
148.9, 163.1 (d, JCF =249.2 Hz), 178.8; m/z 418 (100, MH+); HRMS
CAUTION: Thallium(III) compounds are extremely toxic by
inhalation, skin contact and ingestion.
(ES): MH+, found 418.0248. C23H14NO79BrF+ requires 418.0248.
8‑Bromo‑4‑(4‑chlorophenyl)‑2‑phenyl‑4H‑pyrrolo[3,2,1‑ij]
quinolin‑6‑one (3c): Yield (0.168 g, 65%), m.p. 286–288 °C (EtOH);
Rf (20% ethyl acetate–hexane) 0.54; νmax (ATR) 679, 759, 828, 1279,
1454, 1592, 1636 cm–1; δH (300 MHz, CDCl3) 6.29 (s, 1H), 6.74 (s, 1H),
6.95–7.07 (m, 8H), 8.04 (d, J=1.8 Hz, 1H), 8.33 (d, J=1.8 Hz, 1H);
δC (75 MHz, CDCl3) 110.8, 118.2, 118.9, 123.4, 124.9, 127.9, 128.0,
128.3, 129.0, 129.1, 129.4, 130.3, 130.7, 131.0, 131.3, 135.7, 143.2,
143.7, 178.8; m/z 433 (100, MH+); HRMS (ES): MH+, found 433.9945.
C23H14NO35Cl79Br+ requires 433.9947.
Typical procedure for the dehydrogenation of 1a–d with thallium(III)
p‑tolysulfonate (TTS)
A stirred mixture of 1 (1 equiv.) and TTS (1.2 equiv.) in DME (10 mL
mmol–1 of 1) was heated for 30 minutes under reflux. The solvent was
evaporated under reduced pressure and the residue was dissolved in
chloroform (50 mL). The organic solution was washed with water,
dried over MgSO4 and then evaporated under reduced pressure. The
solid product was recrystallised from ethanol to m.p. 212–214 °C (lit.11
212–213 °C), 2b (0.80 g, 80%), m.p. 222–224 °C (lit.11 225–227 °C),
2c (0.88 g, 88%), m.p. 235–237 °C (lit.11 237–239 °C) and 2d (0.82 g,
82%), m.p. 199–201 °C (lit.11 200–201 °C).
8‑Bromo‑4‑(4‑methoxyphenyl)‑2‑phenyl‑4H‑pyrrolo[3,2,1‑ij]
quinolin‑6‑one (3d): Yield (0.162 g, 62%), m.p. 179–181 °C (EtOH);
Rf
(20% ethyl acetate–hexane) 0.20; νmax (ATR) 691, 759, 828, 1242,
1269, 1399, 1505, 1600, 1636 cm–1; δH (300 MHz, CDCl3) 3.71 (s, 3H),

538 JOURNAL OF CHEMICAL RESEARCH 2014
6.30 (s, 1H), 6.51 (d, J=9.3 Hz, 2H), 7.04 (s, 5H), 7.05 (d, J=9.3 Hz,
2H), 7.72 (s, 1H), 8.01 (d, J=1.2 Hz, 1H), 8.33 (d, J=1.2 Hz, 1H); δC
(75 MHz, CDCl3) 55.3, 110.7, 117.8, 118.6, 123.5, 124.8, 125.2, 127.7,
127.9, 128.7, 129.3, 130.5, 130.6, 131.4, 134.3, 135.5, 143.5, 150.0,
160.4, 179.0; m/z 430 (100, MH+); HRMS (ES): MH+, found 430.0443.
C24H17NO279 Br+ requires 430.0443.
8‑(4‑Fluorophenyl)‑4‑(4‑methoxyphenyl)‑2‑phenyl‑4H‑pyrrolo‑
[3,2,1‑ij]quinolin‑6‑one (4d): Yield (0.051 g, 63%), m.p. 232–234 °C
(EtOH); Rf (30% ethyl acetate–hexane) 0.48; νmax (ATR) 758, 831,
1201, 1246, 1461, 1507, 1597, 1636 cm–1; δH (300 MHz, CDCl3) 3.71 (s,
3H), 6.35 (s, 1H), 6.52 (d, J=7.5 Hz, 2H), 6.83 (s, 1H), 7.05 (s, 5H),
7.08 (d, J=7.5 Hz, 2H), 7.18 (t, J=8.7 Hz, 2H), 7.69 (t, J=8.4 Hz, 2H),
8.09 (s, 1H), 8.41 (s, 1H); δC (75 MHz, CDCl3) 55.3, 111.7, 113.2, 115.8
Typical procedure for the Suzuki–Miyaura cross‑coupling of 3a–d to
afford 4a–d
2
(d, JCF =21.4 Hz), 117.9, 121.0, 122.7, 124.9, 125.5, 127.6, 127.7 (d,
4
3JCF =7.4 Hz), 129.2, 129.3, 129.5, 130.5, 131.8, 136.3 (d, JCF 3.2 Hz),
8‑(4‑Fluorophenyl)‑2,4‑diphenyl‑4H‑pyrrolo[3,2,1‑ij]quinolin‑6‑one
(4a): A mixture of 3a (0.50 g, 1.32 mmol), 4‑fluorophenylboronic acid
(0.21 g, 1.6 mmol), PdCl2(PPh3)2 (0.043 g, 0.07 mmol), PCy3 (0.037 g,
0.13 mmol) and K2CO3 (0.37 g, 2.7 mmol) in dioxane‑water (3:1, v/v;
25 mL) in a three‑necked flask equipped with a stirrer, condenser, and
rubber septum was flushed with nitrogen for 30 min and then heated
at reflux for 6 h under nitrogen atmosphere. The cooled mixture
was added to a beaker containing ice‑cold water and the product
was extracted into ethyl acetate. The combined organic layers were
dried over anhydrous MgSO4, filtered and evaporated under reduced
pressure. The residue was purified by column chromatography on
silica gel using ethyl acetate–hexane mixture as eluant to afford 4a as
a yellow solid (0.43 g, 69%), m.p. 238–240 °C (EtOH); Rf (30% ethyl
acetate–hexane) 0.64; νmax (ATR) 697, 755, 839, 1225, 1465, 1598,
1639 cm–1; δH (300 MHz, CDCl3) 6.38 (s, 1H), 6.84 (s, 1H), 7.00–7.22
(m, 7H), 7.19 (t, J=8.4 Hz, 2H), 7.20 (d, J=8.7 Hz, 2H), 7.71 (t,
J=8.4 Hz, 2H), 8.12 (s, 1H), 8.42 (s, 1H); δC (75 MHz, CDCl3) 111.7,
115.7 (d, 2JCF =21.4 Hz), 118.3, 121.0, 122.6, 125.0, 127.6, 127.8, 127.9,
129.1, 129.2 (d, 3JCF =8.0 Hz), 129.3 (2×C), 129.6, 131.6, 133.2, 136.2,
1
137.1, 137.8, 142.9, 149.8, 160.3, 162.6 (d, JCF =245.6 Hz), 180.2; m/z
446 (100, MH+); HRMS (ES): MH+, found 446.1562. C30H21NO2F+
requires 446.1556.
The authors are grateful to the University of South Africa and
the National Research Foundation (NRF) in South Africa for
financial assistance.
Received 9 June 2014; accepted 2 August 2014
Paper 1402712 doi: 10.3184/174751914X14097554893763
Published online: 25 September 2014
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2
4
1
136.9 (d, JCF =3.2 Hz), 137.8, 142.9, 149.8, 162.6 (d, JCF =245.6 Hz),
180.1; m/z 416 (100, MH+); HRMS (ES): MH+, found 416.1462.
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3
4
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4,8‑Bis(4‑fluorophenyl)‑2‑phenyl‑4H‑pyrrolo[3,2,1‑ij]quinolin‑
6‑one (4b): Yield (0.034 g, 57%), m.p. 270–272 °C (EtOH); Rf (30%
ethyl acetate–hexane) 0.58; νmax (ATR) 759, 834, 1229, 1417, 1502,
1598, 1639 cm–1; δH (300 MHz, CDCl3) 6.34 (s, 1H), 6.71 (d, J=8.7 Hz,
2H), 6.84 (s, 1H), 7.06 (s, 5H), 7.12–7.21 (m, 4H), 7.70 (t, J=8.4 Hz,
2H), 8.11 (s, 1H), 8.41 (s, 1H); δC (75 MHz, CDCl3) 111.8, 115.0 (d,
5
6
7
8
9
M. Layek, A.V.D. Rao, V. Gajare, D. Kalita, D.P. Barange, A. Islam, K.
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M. Layek, V. Gajare, D. Kalita, A. Islam, K. Mukkanti and M. Pal,
Tetrahedron Lett., 2009, 50, 3867.
2
2JCF =21.4 Hz), 115.9 (d, JCF =21.3 Hz), 118.3, 121.1, 122.6, 125.1,
3
4
127.8, 128.1, 129.2 (d, JCF =8.0 Hz), 129.3 (d, JCF =3.2 Hz), 129.4,
3
4
129.5, 130.0 (d, JCF =8.0 Hz), 131.5, 136.2, 136.9 (d, JCF =3.2 Hz),
138.0, 142.6, 148.7, 162.7 (d, 1JCF =245.6 Hz), 163.1 (d, 1JCF =249.3 Hz),
180.0; m/z 434 (100, MH+); HRMS (ES): MH+, found 434.1357.
C29H18NO F2+ requires 434.1356.
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4‑(4‑Chlorophenyl)‑8‑(4‑fluorophenyl)‑2‑phenyl‑4H‑pyrrolo[3,2,1‑
ij]quinolin‑6‑one (4c): Yield (0.033 g, 62%), m.p. 276–278 °C (EtOH);
Rf (30% ethyl acetate–hexane) 0.68; νmax (ATR) 759, 829, 843, 1201,
1463, 1592, 1639 cm–1; δH (300 MHz, CDCl3) 6.34 (s, 1H), 6.84 (s, 1H),
6.97 (d, J=8.7 Hz, 2H), 7.04–7.10 (m, 5H), 7.19 (t, J=8.4 Hz, 2H), 7.20
(d, J=8.7 Hz, 2H), 7.69 (t, J=8.4 Hz, 2H), 8.11 (s, 1H), 8.41 (s, 1H);
δC (75 MHz, CDCl3) 111.8, 115.9 (d, 2JCF =21.4 Hz), 118.2, 121.1, 122.6,
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3
125.2, 127.8, 127.9, 128.1, 129.2 (d, JCF =8.0 Hz), 129.5, 129.6, 130.3,
4
131.4, 131.6, 135.5, 136.1, 136.9 (d, JCF =3.2 Hz), 138.0, 142.6, 148.5,
1
162.7 (d, JCF =245.6 Hz), 180.0; m/z 450 (100, MH+); HRMS (ES):
MH+, found 450.1052. C29H18NOF35Cl+ requires 450.1061.