(Benz)Imidazole-Directed Cobalt(III)-Catalyzed C–H Activation of Arenes: A Facile Strategy to Access Polyheteroarenes by Oxidative Annulation

Article abstract of DOI:10.1002/ejoc.201801056

A facile cobalt(III) catalyzed C–H activation of arenes with substituted (benz)imidazoles as directing groups (DG) is reported. The strategy was utilized for the synthesis of polyheteroarenes when appropriate substrates were treated with diarylacetylenes as the coupling partner. The desired compounds were synthesized in moderate to excellent yield. A putative reaction mechanism is proposed. The final compounds revealed photoluminescence properties.

Full text of DOI:10.1002/ejoc.201801056

A Journal of
Accepted Article
Title: (Benz)Imidazole directed cobalt (III) catalysed C-H activation
of Arenes: A facile strategy to access polyheteroarenes via
oxidative annulation
Authors: Subhabrata Sen and Pratip Kumar Dutta
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
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content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801056
Link to VoR: http://dx.doi.org/10.1002/ejoc.201801056
Supported by

10.1002/ejoc.201801056
European Journal of Organic Chemistry
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(Benz)Imidazole directed cobalt (III) catalysed C-H activation of Arenes: A facile
strategy to access polyheteroarenes via oxidative annulation
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Mr. Pratip Kumar Duttaa and Dr. Subhabrata Sen*, a, b
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a Department of Chemistry, School of Natural Sciences, Shiv Nadar University, Dadri,
Chithera, Gautam Buddha Nagar, Uttar Pradesh 201314, India
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b Department of Chemistry, SRM University-AP, Amaravati
Andhra Pradesh 522502, India
Email: subhabrata.s@srmap.edu.in
Abstract
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A facile cobalt (III) catalysed C-H activation of arenes with substituted ((benz)imidazoles as
directing groups (DG) is reported. The strategy was utilized for the synthesis of
polyheteroarenes when appropriate substrates were reacted with diarylacetylenes as the
coupling partner. The desired compounds were synthesized in moderate to excellent yield. A
putative reaction mechanism is proposed. The final compounds revealed photoluminescence
properties.
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TOC Graphic
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Introduction
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By virtue of constructing complex organic molecules in a step economical fashion,
functionalization of unreactive C-H bond has inarguably emerged as one of the most important
tools in the recent past.1,2 Accordingly, developing novel catalytic methods to activate the
unreactive C-H bonds towards the formation of C-C and C-X (heteroatom) bond is highly
desirable. It is noteworthy that along with catalysts, the success of such reactions also depend
on careful choice directing groups (DG). In this regard, second row transition metals like
ruthenium (Ru) and rhodium (Rh) are well explored as catalysts to activate unreactive C-H
bonds in benzene rings along with diverse DGs such as pyrrolidine, N-chloroamides,
sulfonamides, carboxylic acids and etc.3,4 Despite their high catalytic activity and broad
reaction scope, their moisture sensitivity and high cost have left chemists in quest for an earth
abundant, air stable, cheap metal catalyst to facilitate the similar catalytic activities.5 Majority
of first row transition metals, regardless of exhibiting all these desired qualities, proven to be
less effective due to their unwanted strong chelation with heteroatoms viz. N and S.
Interestingly in the recent years cobalt catalysts are emerging as a promising alternatives devoid
of such disadvantages observed in other first row transition metal catalysts, for C-H activation
reactions. For example Daugulis et al. reported a cobalt acetate (tetrahydrate) catalysed
synthesis of polyaryl heterocycles using 8-aminoquinolineas a DG.6 Later Sundararaju and co-
workers demonstrated a facile C(sp2)-H activation towards alkynes followed by annulation,
with a Cp*Co(III) catalyst and carboxylic acid as the directing group.7A similar reaction was
reported by Zhu and co-workers with the same catalyst but with N-chloroamides as the DG.8
In addition to these, cobalt has proven to be a successful metal catalyst for C-H activation
mediated several other functionalization such as cyanation, halogenation and allylation.9
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The polycyclic N-heteroaryl molecular framework with fused aromatic core has drawn
profound interest owing to their medicinal, electrochemical and optoelectronic properties. They
are obtained in alkaloids which display diverse biological activities as janus kinase inhibitors,
1, anti-viral, 2, anti-tumor agents 3 (Figure 1) and many more.10 The densely packed aromatic
skeleton of the compounds bring about their enhanced ability to act as a charge carrier and
fluorescent emitter in the solid state.11a This in turn has opened a new doorway towards the
fabrication of devices like organic semiconductor and organic light emitting diodes (OLED).11b
In spite of the importance of these compounds and a plethora of functional group directed C-H
activation and subsequent oxidative annulation of arenes, there are not very many syntheses to
afford them.12 Herein we have demonstrated (benz)imidazole directed cobalt catalysed tandem
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functionalization of C-H bond followed by oxidative annulation of benzene rings to afford
(benz)imidazoloisoquinoline (representing polycyclic N-heteroaryl class of molecules) 4a-z
and 4aa-ac in moderate to excellent yield.
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Figure 1. Representative polycyclic N-heteroaryl bearing bioactive compounds
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Results and discussion
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To investigate the feasibility of our reaction, 2-phenylimidazole and diphenylacetylene were
considered as model reaction partners. The reaction was carried in trifluoroethanol (TFE) as
solvent under various conditions viz. cobalt sources as catalyst (5 mol%), additives and
temperature. The details of the exploratory reactions are summarized in table 1. The readily
available cobalt sources like Co(OAc)2, Co(acac)2 and CoBr2 did not afford any product (Table
1, entry 1-3), where pivalic acid was used as additive. Applying Cp*Co(III) based catalyst 3a,
along with silver hexafluoroantimonate, AgSbF6 as the additive, led to the formation of the
desired product 4a, albeit in moderate yield of 54% (Table 1, entry 4). Interestingly, reaction
in absence of the additive provided 4a in 34% yield (Table 1, entry 5). Next we utilized a
dimeric Cp*Co(III) complex 3b as the catalyst for this reaction. To our utmost pleasure the
yield drastically enhanced to 78% (Table 1, entry 6). In a bid to incorporate an additive more
robust than AgSbF6 (susceptible to air and moisture degradation) trial reaction with AgOAc
resulted in slight increase of yield (80%) (Table 1, entry 7). Reaction at lower temperature (60
oC) enhanced the yield further (93%) (Table 1, entry 8). However when 5a was reacted with
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6a in presence of catalyst, sodium acetate but in absence of silver acetate (Table 1, entry 9),
the yield of 4a in the reaction deteriorated (~35%). Other additives such as potassium
hexafluorophosphate (KPF6) or sodium tetrafuoroborate (NaBF4) (Table 1, entries 10 and 11)
resulted in no further improvement of yield. Interestingly, reaction under inert atmosphere
(Table 1, entry 12) generated 4a in poor yield (~30%), thereby emphasizing the contribution
of air in the reaction. Hence the optimized procedure included reaction of 1 equiv. of 5a with
1 equiv. of diphenyl acetylene 6a in presence of dimeric Co(III) complex [Cp*CoI2 ]2 as catalyst
(10 mol%) with silver acetate (AgOAc) as additive (20 mol%) in 2,2,2-trifluoroethanol (TFE)
at 60 °C to afford the desired 4a in 93% yield.
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Table 1. Optimization of reaction conditionb
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Entry
1.
Co-catalyst
Base
Additive (mol %)
Pivalic acid (200)
Temp. ( oC) Yield (%)a
(equiv.)
Co(OAc)2.4H2O Na2CO3 (2)
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0
2.
3.
Co(acac)2
CoBr2
Pivalic acid (200)
0
0



-


4.
Cp*Co(CO)I2
AgSbF6 (20)
-
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34c
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80
93
35
22
0

5.



6.
[Cp*CoI2]2
K2CO3 (2)
KOAc (2)
NaOAc (2)
AgSbF6 (20)
AgOAc (20)

7.







8.
60

9.
-








10.
11.
12.d
KPF6 (20)
NaBF4 (20)
AgOAc (20)
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a Isolated yield; b Reaction scale: 0.7 mmole of 5a and 0.7 mmole of 6a, cYield in absence of
AgSbF6; d Under argon atmosphere
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With the optimised protocol in hand, we set out to assess the substrate scope of our catalyst
with benzimidazole as DG, for the oxidative annulation reactions between 2-
arylbenzimidazoles 5b-n and symmetrical and unsymmetrical diarylacetylenes 6a-e (Figure 2).
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Figure 2. Reactions of various benzimidazoles and diarylacetylenes
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To begin with the reaction of 5b-n with diphenyl acetylene afforded the desired products 4b-j,
l and s-w, in excellent yield of 85-90%. Interestingly the reaction of 5h afforded two regiomers,
4h and I (Figure 2). Reaction of 5k and m with diphenyl acetylene, 6a, also afforded regiomers
4s/t and u/v, in equimolar mixture with an overall yield of 76% and 97% respectively (Figure
2).
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Next, reactions of 5b, c, e, f and k with bis(4-bromophenyl)acetylene, 6b, bis(3-
fluorophenyl)acetylene, 6c and bis(4-tolyl)acetylene, 6d, afforded 4k,m-r in moderate to
excellent yield (71-83%). It was noteworthy, that the electron withdrawing groups at the
benzene ring of the acetylenes favoured the reaction whereas the electron donating groups
proved detrimental (Figure 2).
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During the reaction of 5b with 4-chlorophenyl-2-thiophenylacetylene 6e, only the major
diastereomer 4ae could be isolated. Reaction with phenyl acetylene or with phenyl-2-isoproply
acetylene rendered the reaction inactive (Figure 2).
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The structures of the desired compounds were confirmed by the single crystal X-ray of the
representative molecules 4u and 4v (Figure 3).
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Figure 3. Single crystal X-Ray of 4u and v
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Next, imidazoles were screened for their ability to induce the C-H activation and subsequent
annulation with our cobalt catalyst. Accordingly, 2-phenylimidazole, 5a was reacted with 6a-
d to afford the desired compounds 4a and 4x-z in decent yield of 81-88% (Figure 4). The
corresponding 4-methylimidazole substrate 5l when reacted with diphenylacetylene, afforded
the corresponding product 4aa in moderate yield of 72% (Figure 4). Interestingly when it was
further reacted with bis(2-fluorophenyl)acetylene, 6e, afforded equimolar mixtures 4ab and
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4ac in 92% over all (Figure 4). Next reaction of 5a with 4-chlorophenyl-2-thiophenylacetylene
afforded the desired compound 4ad in 39% yield.
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Figure 4. Reactions of various imidazoles and diarylacetylenes
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To understand the mechanism of transformation we conducted several control experiments as
depicted in Scheme 1. Reaction between 5a and 6a in the absence of the catalyst or the oxidant
AgOAc (Scheme 1a and b) could not provide the desired compounds, thereby indicating their
indispensability in the reaction. When they were reacted in presence of radical scavenger
TEMPO (Scheme 1c), the reaction rate remain unchanged, there by indicating that the reaction
proceeded through ionic pathway.
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Scheme 1. Control experiments to delineate the reaction mechanism
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Based on our control experiments and the previously reported similar methodologies, a
plausible reaction mechanism is depicted in Scheme 2 with the representative reaction partners
5a and 6a.13 Initial iodide abstraction from the dimeric cobalt complex by AgOAc and
subsequent co-ordination of the resulting species with the nitrogen atom of 5a may result into
complex I. A concerted metallation-deprotonation (CMD) assisted C-H activation then affords
the formation of the cobaltacycle II. Co-ordinative unsaturation may induce the complexation
of II with alkyne which ultimately leads to the seven membered intermediate IV. This, in the
subsequent step leads to the formation of the desired product 4a and Cp*Co(I). Ag (I) reoxidize
the Co(I) to Co(III) which is the active species for the next catalytic cycle.
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Scheme 2. Plausible mechanism of transformation for [Cp*CoI2]2 catalyzed C-H activation
and subsequent oxidative annultion of benzene rings toward alkyne
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To investigate the utility of our novel polyaryl olefins, the steady state emission and
photoluminescence (PL) experiments were executed for compound 4c (Figure 5) in
dichloromethane. Emission at 407 nm with wide PL band in the visible range was observed.
The existence of continuous  conjugation in our molecules unambiguously modulates the PL
band. We envision that due to their fluorescence properties our molecules may have application
as fluorescent labels in macromolecular studies.
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Figure 5. PL-spectra of 4c in dichloromethane (1 X 10-6 M) and picture of 4c in
dichloromethane under the UV lamp
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Conclusion
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In conclusion, we mention that 2-aryl(benz)imidazole substrates have been used to demonstrate
cobalt catalyzed C-H functionalization. The (benz)imidazole functionality on the substrate is
harnessed for directing C-H functionalization reactions on the arenes for the construction of
polyaryl olefins. Unactivated alkynes as reaction partners provide facile access to the final
compounds. The wide substrate scope affords the ability to include diverse range of
functionalities as substituents into the final scaffold. Control experiments provided crucial
insights to propose a reaction pathway to afford the products. The desired final compounds
demonstrated fluorescence properties which in turn makes these potential candidates as
fluorescent labels in macromolecular studies. Presently this is being investigated in our lab.
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Experimental
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General. All reactions were carried out under N2 atmosphere as specified. Reaction was
monitored by thin layer chromatography (TLC, Silica gel 60 F254), using UV light to visualize
the course of the reaction. 2-aryl(benz)imidazoles 5a-l were procured from multiple
commercial vendors. 1H NMR and 13C NMR spectra were recorded with tetramethylsilane as
an internal standard at ambient temperature unless otherwise indicated with Bruker 400 MHz
1
instruments at 400 MHz for H NMR and 100 MHz for 13C NMR spectroscopy. Splitting
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patterns are designated as singlet (s), broad singlet (br, s), doublet (d), triplet (t). Splitting
patterns that could not be interpreted or easily visualized are designated as multiplet (m). Mass
spectrometry analysis was done with a 6540 UHD Accurate-Mass QTOF LC-MS system
(Agilent Technologies) equipped with an Agilent 1290 LC system obtained by the Department
of Chemistry, School of Natural Sciences, Shiv Nadar University, Uttar Pradesh 201314, India.
HPLC experiments were carried out in Agilent Eclipse Plus C18 column.
General protocol for the synthesis of polyheteroarenes 4a-4ae
An oven dried screw capped pressure tube, equipped with magnetic stir bar, was charged with
2-phenylimidazole (100 mg, 0.7 mmole), diphenyl acetylene (123 mg, 0.7 mmole), [Cp*CoI2]2
(62 mg, 0.07 mmole), AgOAc (23 mg, 0.14 mmole) and NaOAc (113 mg, 1.38 mmole) in 2,
2, 2-trifluoroethanol and allowed to stir at 60oC under air for 12 hours. The crude reaction
mixture was then filtered through a plug of celite and washed with EtOAc. The solvent was
removed under reduced pressure and purified by column chromatography using the indicated
eluent.
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5,6-diphenylimidazo[2,1-a]isoquinoline (4a): EtOAc/n-hexane (15%); Yellow crystalline
solid, 1H NMR (400 MHz, CDCl3) δ 8.76 (d, J= 8 Hz, 1H), 7.64 (t, J= 8 Hz, 1H), 7.55 (s, 1H),
7.48 (t, J= 8 Hz, 1H), 7.39 (d, J= 8 Hz, 1H), 7.34-7.33 (m, 1H), 7.32 (bs, 2 H), 7.30 (s, 1H),
13
7.29-7.28 (m, 1H), 7.27-7.26 (m, 2H), 7.25-7.23 (m, 1H), 7.21-7.19 (m, 3H). C NMR (100
MHz, CDCl3) δ 143.08, 135.93, 133.48, 131.42, 13.83, 130.63, 130.22, 128.86, 128.66, 128.06,
127.86, 127.31, 126.45, 124.49, 123.20, 122.63, 113.95. HRMS (EI+) m/z calcd.
forC23H16N2[M]+ : 320.1313, found: 320.1316
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5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4b): EtOAc/n-hexane (7%); Yellow
crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.99 (d, J = 8 Hz, 1H), 7.99 (d, J = 8 Hz, 1H),
7.69 (t, J = 8 Hz, 1H), 7.60-7.56 (m, 1H), 7.45-7.41 (m, 1H), 7.39 (s, 1H), 7.35 (t, J = 8 Hz,
4H), 7.31-7.29 (m, 1H), 7.27 (d, J = 4 Hz, 2H), 7.24-7.21 (m, 2H), 6.93 (t, J = 8 Hz, 1H), 6.01
(d, J = 8 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 147.79, 144.31, 135.70, 135.15, 132.67,
131.53, 131.23, 13.66, 129.88, 129.23, 128.75, 128.03, 127.76, 127.27, 126.38, 125.08, 124.12,
123.54, 122.97, 121.24, 119.60, 114.14. HRMS (EI+) m/z calcd. for C27H18N2 [M]+ : 370.1470,
found: 370.1472
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7,8-diphenylbenzo[h]benzo[4,5]imidazo[2,1-a]isoquinoline (4c): EtOAc/n-hexane (5 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 11.06 (d, J = 8 Hz, 1H), 8.05 (d, J = 8
Hz,
1H), 7.93-7.89 (m, 2H), 7.86 (d, J = 8 Hz, 1H), 7.65 (t, J = 8 Hz, 1H), 7.37-7.33 (m, 5H), 7.30-
7.29 (m, 2H), 7.25-7.21 (m, 3H), 7.19-7.17 (m, 3H), 6.91-6.87 (m, 1H), 6.02 (d, J = 8 Hz, 1H).
13C NMR (100 MHz, CDCl3) δ 197.01, 147.93, 144.72, 136.49, 136.19, 134.09, 132.65,
132.55, 131.81, 130.93, 130.64, 130.29, 129.98, 129.32, 129.24, 128.91, 128.42, 128.35,
128.18, 127.37, 126.95, 124.45, 124.12, 124.09, 121.19, 119.96, 118.16, 114.51, 77.38, 77.13,
76.87. HRMS (EI+) m/z calcd. forC31H20N2 [M]+ : 420.1626, found: 420.1619
5,6-diphenylbenzo[4,5]imidazo[2,1-a][2,6]naphthyridine (4d): EtOAc/n-hexane (20 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.87-8.74 (m, 3H), 8.03 (d, J = 8 Hz,
1H), 7.46-7.40 (m, 4H), 7.36-7.35 (m, 2H), 7.30 (t, J = 8 Hz, 3H), 7.25-7.23 (m, 2H), 7.01 (t,J
= 8 Hz, 1H), 6.05 (d, J = 12 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 144.32, 133.98, 133.07,
131.48, 131.23, 130.57, 129.70, 129.03, 128.35, 127.85, 124.87, 122.59, 120.31, 12.29, 114.51,
100.00. . HRMS (EI+) m/z calcd. forC26H17N3 [M]+ : 371.1422, found: 371.1421
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3-methoxy-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4e): EtOAc/n-hexane (12
%); brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.93 (d,J = 8 Hz, 1H), 7.97 (d,J =
8 Hz, 1H), 7.45-7.40 (m, 3H), 7.39-7.35 (m, 3H), 7.33-7.31 (m, 2H), 7.29-7.27 (m, 2H), 7.25-
7.23 (m, 2H), 6.92 (t, J = 8 Hz, 1H), 6.76 (s, 1H), 3.79 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
161.02, 148.01, 144.47, 135.71, 135.65, 134.59, 133.82, 133.44, 131.19, 130.59, 129.16,
128.70, 128.06, 127.28, 126.97, 123.96, 123.19, 120.74, 119.23, 116.86, 116.35, 113.95,
108.83, 55.33. . HRMS (EI+) m/z calcd. forC28H20N2O [M]+ : 400.1576, found: 40.1573
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3-methyl-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4f): EtOAc/n-hexane (5 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.88 (d, J = 8 Hz, 1H), 7.96 (d,J = 8 Hz,
1H), 7.53 (d, J = 8 Hz, 1H), 7.43-7.42 (m, 1H), 7.40-7.38 (m, 2H), 7.37-7.35 (m, 1H), 7.34-
7.33 (m, 1H), 7.32-7.30 (m, 1H), 7.29-7.27 (m, 2H), 7.25-7.22 (m, 2H), 7.20 (bs, 1H), 7.11
(s,1H), 6.91 (t, J = 8 Hz, 1H), 5.99 (d, J = 8 Hz, 1H), 2.43 (s, 3H). 13C NMR (100 MHz, CDCl3)
δ 148.06, 144.41, 140.40, 135.85, 135.24, 133.91, 132.84, 131.62, 131.27, 130.74, 129.46,
129.26, 128.81, 128.09, 127.30, 126.20, 125.11, 124.11, 123.47, 121.08, 120.71, 119.49,
114.16, 22.15. HRMS (EI+) m/z calcd. forC28H20N2 [M]+ : 384.1626, found: 384.1625
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3-chloro-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4g): EtOAc/n-hexane (8 %);
white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.92 (d, J = 8 Hz, 1H), 7.97 (d, J = 8 Hz,
1H), 7.66-7.63 (m, 1H), 7.45-7.43 (m, 1H), 7.421-7.38 (m, 3H), 7.36-7.32 (m, 3H), 7.31-7.27
(m, 3H), 7.21-7.18 (m, 2H), 6.96-6.92 (m, 1H), 6.00 (d, J = 8 Hz, 1H). 13C NMR (100 MHz,
CDCl3) δ 147.24, 144.35, 136.45, 136.29, 133.46, 131.50, 131.22, 130.53, 129.51, 128.93,
128.37, 128.35, 128.68, 126.73, 125.84,124.48, 122.70, 121.63, 121.37, 114.26. HRMS (EI+)
m/z calcd. forC27H17ClN2 [M]+ : 404.1080, found: 404.1079
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4-fluoro-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4h): EtOAc/n-hexane (8 %);
white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.84 (d, J = 8 Hz, 1H), 7.98 (dJ = 8 Hz,
1H), 7.65 (sex, J = 4 Hz, 1H), 7.41-7.35 (m, 5H), 7.31-7.30 (m, 1H), 7.29-7.28 (m, 1H), 7.25-
7.23 (m, 1H), 7.21-7.20 (m, 3H), 7.19-7.17 (m, 1H), 6.94 (t, J = 8 Hz, 1H), 5.91 (d, J = 8 Hz,
1H). 13C NMR (100 MHz, CDCl3) δ 160.18 157.64, 144.31, 137.60, 136.53, 133.30, 130.69,
130.59 (d, JF = 3 Hz), 129.22, 128.77, 128.67, 127.31, 126.79, 125.05, 124.41, 121.65, 121.31,
121.27, 121.15, 119.72, 119.37, 117.00, 116.78, 114.21. HRMS (EI+) m/z calcd. forC27H17FN2
[M]+ : 388.1376, found: 388.1372.
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2-fluoro-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4i): EtOAc/n-hexane (8 %);
white crystalline solid, 1H NMR (400 MHz, CDCl3) δ8.76 (d, J = 8 Hz, 1H), 7.67 (t, J = 8 Hz,
1H), 7.57 (s,1H), 7.52-7.49 (m, 1H), 7.37-7.33 (m, 2H), 7.30-7.28 (m, 1H), 7.18 (s,1H), 7.11-
7.08 (m, 1H), 7.07-7.04 (m, 1H), 7.02-6.97 (m, 3H), 6.95-6.91 (t, J = 8 Hz, 1H). 13C NMR (100
MHz, CDCl3) δ 163.20, 160.72, 144.22, 135.51, 133.54, 131.42, 131.24, 130.67, 129.28,
128.99, 128.95 (d, JF = 8 Hz), 128.77, 128.10, 127.41, 124.30, 121.57, 119.76, 118.45, 118.22,
114.21, 110.47, 110.23. HRMS (EI+) m/z calcd. form/z calcd. For C27H17FN2 [M]+ : 388.1376,
found: 388.1378
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5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline-3-carbonitrile (4j ): EtOAc/n-hexane
(15 %); white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 9.07(d, J = 8 Hz, 1H), 8.01 (d,
J = 8 Hz, 1H), 7.89-7.87 (m, 1H), 7.66 (s,1H), 7.48-7.44 (m, 1H), 7.44-7.43 (m,1H), 7.42 (bs,
1H), 7.41-7.40 (m,1H), 7.35-7.33 (m, 1H), 7.34-7.32 (m, 2H), 7.31 (bs, 1H), 7.31-7.30 (bs,
1H), 7.20-7.18 (m, 2H), 7.02-6.98 (m, 1H), 6.02 (d, J = 4 Hz, 1H). 13C NMR (100 MHz, CDCl3)
δ 146.25, 144.40, 137.13, 134.35, 133.07, 132.66, 131.40, 131.25, 131.23, 130.38, 129.75,
129.60, 129.06, 128.57, 128.04, 126.03, 125.69, 124.92, 122.56, 122.48, 120.16, 118.81,
114.43, 113.13, 77.37, 77.11, 76.86. HRMS (EI+) m/z calcd. For C28H17N3[M]+ : 395.1422,
found: 395.1426
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7,8-bis(4-bromophenyl)benzo[h]benzo[4,5]imidazo[2,1-a]isoquinoline (4k): EtOAc/n-
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hexane (12 %); white crystalline solid, H NMR (400 MHz, CDCl3) δ 11.11 (d, d, J = 8 Hz,
1H), 8.14 (d, d, J = 4 Hz, 1H), 8.01-7.94 (m, 3H), 7.76-7.73 (m, 1H), 7.60-7.58 (m, 2H), 7.50-
7.47 (m, 2H), 7.46-7.45 (m, 1H), 7.33 (d, d, J = 8 Hz, 1H), 7.25-7.23 9m, 2H), 7.12-7.10 (m,
2H), 7.06-7.02 (m, 1H), 6.18 (d, J = 4 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 147.79, 144.76,
135.24, 134.87, 133.32, 132.74, 132.71, 132.48, 132.17, 131.92, 131.70, 131.19, 130.20,
129.74, 129.28, 128.61, 128.41, 127.22, 124.70, 123.98, 123.62, 123.16, 121.96, 120.24,
118.44, 114.16.HRMS (EI+) m/z calcd. forC31H18Br2N2 [M]+ : 690.9814, 692.9796, found:
690.9811, 692.9793.
5,6-diphenyl-2,4-bis(trifluoromethyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4l):
EtOAc/n-hexane (10 %); white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 9.00-8.97 (m,
1H), 7.96 (d, J = 4 Hz, 1H), 7.45-7.42 (m, 1H), 7.41-7.40 (m,1H), 7.40 (bs, 1H), 7.39-7.38 (m,
1H), 7.38-7.37 (m,1H), 7.36 (bs, 1H), 7.35-7.34 (m, 1H), 7.34-7.33 (m, 2H), 7.32-7.29 (m, 1H),
7.29-7.27 (m, 1H), 7.21-7.19 (m, 2H), 5.97 (d, J = 8 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ
164.74, 162.76, 147.42, 144.34, 136.40, 135.20, 134.96, 134.89, 133.50, 131.45, 131.21,
130.53, 129.49, 128.92, 128.33, 127.64, 124.38, 123.00, 122.98, 121.41, 119.60, 116.60,
116.41, 114.21, 111.95, 111.76.HRMS (EI+) m/z calcd. forC29H16F6N2 [M]+ : 506.1218,
found: 506.1216.
5,6-bis(4-bromophenyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4m): EtOAc/n-hexane (15
%); white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.98 (d, J = 8 Hz, 1H), 7.99 (d, J =
8 Hz, 1H), 7.71 (t, J = 8 Hz, 1H), 7.61-7.56 (m,3H), 7.46 (d, J = 8 Hz, 2H), 7.40 (t, J = 8 Hz,
1H), 7.28 (d, J = 8 Hz, 1H), 7.21 (d, J = 12 Hz, 2H), 7.07 (d, J = 8 Hz, 2H), 7.01 (t, J = 8 Hz,
1H), 6.10 (d, J = 12 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 147.62, 144.30, 134.40, 133.94,
133.02, 132.31, 132.16, 132.05, 131.56, 130.97, 130.09, 128.18, 126.10, 125.22, 124.39,
123.90, 123.06, 122.66, 121.87, 121.62, 119.84, 113.79, 77.32, 77.00, 76.68.HRMS (EI+) m/z
calcd. forC27H16Br2N2 [M]+ : 526.9753, 528.9734, found: 526.9756, 528.9731.
5,6-bis(4-bromophenyl)-3-methoxybenzo[4,5]imidazo[2,1-a]isoquinoline (4n): EtOAc/n-
hexane (5 %); brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.89 (d, J = 8 Hz, 1H),
7.95 (d,J = 8 Hz, 1H), 7.56 (d,J = 8 Hz, 2H), 7.45 (d,J = 8 Hz, 2H), 7.37 (t,J = 8 Hz, 1H), 7.31-
7.28 (m, 1H), 7.20 (d,J = 8 Hz, 2H), 7.07 (d,J = 8 Hz, 2H), 6.97 (t, J = 8 Hz, 1H), 6.66-6.65
13
(m, 1H), 6.06 (d,J = 8 Hz, 1H), 3.78 (s,3H). C NMR (100 MHz, CDCl3) δ 161.19, 134.48,
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133.96, 133.87, 132.96, 132.29, 132.10, 131.61, 127.19, 124.30, 123.87, 122.33, 121.90,
121.17, 119.44, 116.66, 113.64, 108.70, 55.44. HRMS (EI+) m/z calcd. forC28H18Br2N2O
[M]+ : 556.9859, 558.984, found: 556.9860, 558.9842.
5,6-bis(3-fluorophenyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4o): EtOAc/n-hexane (8 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.99 (d, J = 8 Hz, 1H), 8.00 (d, J = 8
Hz, 1H), 7.72 (t, J = 8 Hz, 1H), 7.63-7.59 (m, 1H), 7.46-7.38 (m, 2H), 7.33-7.28 (m, 2H), 7.20-
7.15 (m, 2H), 7.09-7.06(m, 1H), 7.04-6.98 (m, 3H), 6.96-6.92 (m, 1H), 6.09-6.06 (m, 1H). 13C
NMR (100 MHz, CDCl3) δ 147.67, 144.32, 130.25, 128.34, 127.39, 127.37, 126.59, 126.57,
126.26, 125.27, 124.51, 123.08, 121.73, 119.88, 118.58, 118.56, 118.41,118,.39, 117.93,
117.91, 117.75, 117.74, 116.90, 116.75, 116.73, 114.88, 114.86, 114.72, 114.69, 114.53,
113.83. HRMS (EI+) m/z calcd. forC27H16F2N2 [M]+ : 407.1354, found 407.1355.
5,6-di-p-tolyl-2,4-bis(trifluoromethyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4p):
1
EtOAc/n-hexane (10 %); white crystalline solid, H NMR (400 MHz, CDCl3) δ 8.97-8.95
(m,1H), 7.95 (d, J = 8 Hz, 1H), 7.40-7.35 (m, 2H), 7.20 (s, 3H), 7.11-7.06 (m, 4H), 6.99-6.96
(m, 1H), 6.96-6.92 (m, 1H), 6.02 (d, J = 8 Hz, 1H), 2.42 (s, 3H), 2.33 (s,3H). 13C NMR (100
MHz, CDCl3) δ 164.71, 162.72, 147.47, 144.32, 139.28, 137.13, 136.51, 135.28, 135.21,
132.23, 131.29, 131.24, 130.67, 130.32, 129.62, 129.04, 127.75, 127.68, 124.27, 122.99,
122.96, 121.28, 119.49, 116.41, 116.22, 114.37, 111.95, 111.77, 77.37, 77.12, 76.86, 21.67,
21.37. HRMS (EI+) m/z calcd. forC31H20F6N2 [M]+ : 534.1603, found: 534.1603.
5,6-bis(4-bromophenyl)-3-methylbenzo[4,5]imidazo[2,1-a]isoquinoline (4q): EtOAc/n-
hexane (10 %); white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.86 (d, J = 8 Hz, 1H),
7.97 (d, J = 8 Hz, 1H), 7.57-7.53 (m, 3H), 7.46-7.45 (m, 2H), 7.40-7.37 (m, 1H), 7.21-7.19 (m,
13
1H), 7.07-7.03 (m, 3H), 7.07-6.97 (m, 1H), 6.08 (d, J = 8 Hz, 1H), 2.44 (s, 3H). C NMR
(100 MHz, CDCl3) δ 147.90, 144.38, 140.72, 134.57, 134.02, 133.13, 132.51, 132.38, 132.25,
132.24, 131.64, 131.01, 129.88, 125.95, 125.24, 124.40, 123.92, 123.89, 122.61, 121.88,
121.47, 120.78, 119.74, 113.83, 22.14.HRMS (EI+) m/z calcd. forC28H18Br2N2 [M]+ : 540.991,
542.9891, found: 540.9908, 542.9889.
5,6-bis(4-bromophenyl)-2,4-bis(trifluoromethyl)benzo[4,5]imidazo[2,1-a]isoquinoline
(4r): EtOAc/n-hexane (12 %); white crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.98-8.95
(m,1H), 7.97 (d, J = 8 Hz, 1H), 7.59-7.57 (m,2H), 7.48-7.46 (m, 2H), 7.44-7.39 (m, 2H), 7.22-
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7.20 (m, 1H), 7.07-7.04 (m, 2H), 7.03-6.99 (m, 1H), 6.92 (dd, J1= 4 Hz, J2= 8 Hz, 1H), 6.09
13
(d, J = 4 Hz, 1H). C NMR (100 MHz, CDCl3) δ 164.80, 162.81, 147.24, 144.32, 135.24,
134.30, 134.23, 133.90, 132.96, 132.50, 132.09, 132.03, 131.88, 130.96, 128.03, 127.96,
124.68, 124.20, 122.28, 122.10, 122.07, 121.81, 119.85, 119.65, 119.64, 117.04, 116.86,
113.89, 111.75, 111.56.HRMS (EI+) m/z calcd. forC29H14 Br2F6N2 [M]+ : 662.9501, 664.9482,
found: 662.9502, 664.9479.
9-bromo-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4s): EtOAc/n-hexane (8 %);
1
brown crystalline solid, H NMR (400 MHz, CDCl3) δ 8.88 (d, J = 8 Hz, 1H), 8.03 (s, 1H),
7.63 (t, J = 8 Hz, 1H), 7.52 (t, J = 8 Hz, 1H), 7.38-7.32 (m, 3H), 7.30-7.27 (m, 1H), 7.24-7.20
(m, 3H), 7.19-7.18 (m, 2H), 7.15-7.13 (m, 2H), 6.96-9.93 (m , 1H), 5.76 (d, J = 8 Hz, 1H). 13C
NMR (100 MHz, CDCl3) δ 147.58, 144.60, 134.40, 131.77, 13.40, 129.54, 129.23, 128.41,
127.88, 127.07, 126.95, 126.38, 125.47, 124.18, 123.24, 123.06, 121.72, 121.25, 116.42,
114.20. HRMS (EI+) m/z calcd. forC27H17BrN2[M]+ : 449.0648, 451.0631, found: 449.0647,
451.0633.
10-bromo-5,6-diphenylbenzo[4,5]imidazo[2,1-a]isoquinoline (4t): EtOAc/n-hexane (8 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.89 (d, J = 8 Hz, 1H), 7.77 (d, J = 8
Hz, 1H), 7.64 (t, J = 8 Hz, 1H), 7.56-7.52 (m, 1H), 7.41-7.40 (m, 1H), 7.39-7.35 (m, 2H), 7.30-
7.28 (m, 2H), 7.24 (b, 1H), 7.22-7.21 (m, 2H), 7.20 (s, 2H), 7.17-7.15 (m, 2H), 5.97 (s, 1H).
13C NMR (100 MHz, CDCl3) δ 147.31, 142.13, 134.38, 133.84, 132.23, 131.70, 130.99,
130.40, 129.48, 129.20, 128.50, 127.94, 127.08, 126.98, 126.40, 126.36, 125.51, 124.11,
123.00, 121.80, 119.61, 116.27, 113.12. HRMS (EI+) m/z calcd. forC27H17BrN2[M]+ :
449.0648, 451.0631, found: 449.0645, 454.0630.
5,6-diphenyl-9-(trifluoromethyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4u): EtOAc/n-
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hexane (5 %); white crystalline solid, H NMR (400 MHz, CDCl3) δ 8.99 (d, J = 8 Hz, 1H),
8.26 (s, 1H), 7.73 (t,J = 8 Hz, 1H), 7.62 (t, J = 8 Hz, 1H), 7.44-7.40 (m, 3H), 7.38-7.33 (m,
3H), 7.29 (d, J = 8 Hz, 3H), 7.23 (d, J = 8 Hz, 2H), 7.17 (d,J = 8 Hz, 1H), 6.06 (d,J = 8 Hz,
1H). 13C NMR (100 MHz, CDCl3) δ 149.32, 143.79, 135.29, 134.85, 133.35, 132.85, 131.37,
130.59, 130.50, 129.52, 128.95, 128.12, 127.47, 126.57, 125.30, 124.47, 122.91, 122.77,
117.80, 117.09, 114.56. HRMS (EI+) m/z calcd. forC28H17F3N2 [M]+ : 439.1417, found:
439.1416.
5,6-diphenyl-10-(trifluoromethyl)benzo[4,5]imidazo[2,1-a]isoquinoline (4v): EtOAc/n-
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hexane (5 %); white crystalline solid, H NMR (400 MHz, CDCl3) δ 9.00 (d, J = 8 Hz, 1H),
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8.03(d,J = 8 Hz, 1H), 7.73 (t,J = 8 Hz, 1H), 7.66-7.59 (m, 2H), 7.48-7.43 (m, 3H), 7.40 (t,J =
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8 Hz, 1H), 7.36-7.33(m, 2H), 7.31-7.27 (m, 3H), 7.25-7.24 (m, 2H), 6.20 (s, 1H). C NMR
(100 MHz, CDCl3) δ 149.76, 146.29, 135.23, 134.97, 133.09, 133.00, 131.38, 130.58, 130.48,
129.64, 129.10, 128.15, 128.10, 127.52, 126.52, 125.32, 124.33, 122.67, 12.96, 119.80, 112.14.
HRMS (EI+) m/z calcd. for C28H17F3N2[M]+ : 377.1107, found: 377.1105.
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4,5-diphenylbenzo[4,5]imidazo[1,2-a]thieno[2,3-c]pyridine (4w): EtOAc/n-hexane (10 %);
brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 7.94 (d, J = 8 Hz, 1H), 7.61 (d, J = 8
Hz, 1H), 7.46-7.44 (m 2H), 7.42 (s, 1H), 7.42-7.39 (m, 2H), 7.37-7.35 (m, 3H), 7.26-7.23 (m,
4H), 7.05 (d, J = 8 Hz, 1H), 6.91 (t, J = 8 Hz, 1H), 6.08 (d, J = 8 Hz, 1H). 13C NMR 130.23,
(100 MHz, CDCl3) δ 144.92, 140.35, 136.14, 134.99, 133.26, 130.84, 130.80, 129.39, 129.19,
128.85, 128.00, 127.28, 125.72, 125.27, 124.53, 121.56, 12.70, 119.45, 114.43. HRMS (EI+)
m/z calcd. for C25H16N2S [M]+ : 439.1417, found: 439.1415.
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6-(4-chlorophenyl)-5-(thiophen-2-yl)benzo[4,5]imidazo[2,1-a]isoquinoline (4ae):
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EtOAc/n-hexane (5 %); white crystalline solid, H NMR (400 MHz, CDCl3) δ 9.00 (t, J = 8
Hz, 1H), 8.03-8.01 (m, 1H), 7.77-7.72 (m, 1H), 7.68-7.62 (m, 1H), 7.57-7.52 (m, 1H), 7.48-
7.46 (m, 1H), 7.45-7.41 (m, 1H), 7.38 (d, J = 8 Hz, 1H), 7.36-7.31 (m, 2H), 7.26-7.23 (m, 1H),
13
7.15-7.13 (m, 1H), 7.09-7.04 (m, 1H), 7.03-6.93 (m, 1H), 6.17-6.14 (m, 1H). C NMR (100
MHz, CDCl3) δ 135.88, 135.71, 135.66, 133.97, 133.68, 133.44, 132.84, 132.62, 132.48,
131.97, 131.79, 130.89, 130.30, 130.26, 130.14, 129.22, 128.80, 128.39, 128.27, 127.49,
127.14, 126.86, 126.42, 126.22, 125.24, 125.03, 124.57, 124.49, 121.84, 121.75, 119.75,
119.57, 113.89, 113.89, 113.81. HRMS (EI+) m/z calcd. for C25H15ClN2S [M]+ : 411.0717,
found: 411.0729.
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5,6-di-p-tolylimidazo[2,1-a]isoquinoline (4x): EtOAc/n-hexane (12 %); white crystalline
solid, 1H NMR (400 MHz, CDCl3) δ 8.74 (d, J = 8 Hz, 1H), 7.62 (t, J = 8 Hz, 1H), 7.52 (s, 1H),
7.45 (t, J = 8 Hz, 1H), 7.38 (d, J = 8 Hz, 1H), 7.17 (d, J = 8 Hz, 3H), 7.14-7.12 (m, 2H), 7.08-
7.06 (m, 4H), 2.34 (s 3H), 2.33 (s, 3H). 13C NMR 130.23, (100 MHz, CDCl3) δ 142.12, 137.56,
135.74, 132.47, 132.01, 130.23, 129.89, 129.89, 129.75, 129.71, 129.03, 128.31, 127.75,
126.85, 126.59, 125.44, 123.25, 122.23, 122.09, 112.94, 20.34, 20.22. HRMS (EI+) m/z calcd.
for C25H20N2[M]+ : 348.1626, found: 348.1624.
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5,6-bis(3-fluorophenyl)imidazo[2,1-a]isoquinoline (4y): EtOAc/n-hexane (8 %); white
crystalline solid , 1H NMR (400 MHz, CDCl3) δ 8.76 (d, J = 8 Hz, 1H), 7.67 (t, J = 8 Hz, 1H),
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7.57(s, 1H), 7.50 (t, J = 8 Hz, 1H), 7.37-7.35 (m, 2H), 7.33- 7.28 (m, 1H), 7.18 (br, s, 1H),
7.11-7.06 (m, 2H), 7.04-6.97(m, 3H), 6.95-6.91 (m, 1H). 13C NMR (100 MHz, CDCl3) δ
163.77, 163.74, 163.53, 163.51, 161.79, 161.76, 161.57, 161.54, 143.16, 143.16, 137.91,
137.91, 137.85, 137.85, 135.19, 135.12, 132.15, 131.39, 130.81, 130.81, 130.74, 130.74,
130.71, 130.71, 130.64, 130.64, 130.03, 129.94, 129.92, 129.86, 128.40, 127.29, 127.27,
127.25, 126.30, 126.11, 126.08, 123.61, 123.42, 123.41, 118.47, 118.46, 118.30, 118.29,
117.41, 117.24, 116.53, 116.52, 116.37, 116.35, 114.90, 114.88, 114.73, 114.72, 113.87,
100.00, 77.38, 77.12, 76.87, 0.10. HRMS (EI+) m/z calcd. for C23H14F2N2[M]+ : 357.1198,
found: 357.1120.
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5,6-bis(4-bromophenyl)imidazo[2,1-a]isoquinoline(4z): EtOAc/n-hexane (20 %); white
crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.75 (d,J = 8 Hz, 1H), 7.66 (t,J = 8 Hz, 1H),
7.56-7.50 (m, 3H), 7.49-7.44 (m, 3H), 7.33 (d, J = 8 Hz, 1H), 7.16 (d, J = 8 Hz, 3H), 7.06 (d,
J = 8 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ 143.16, 134.70, 133.03, 132.36, 132.16, 131.85,
131.687, 131.33, 130.13, 128.39, 128.38, 126.25, 123.66, 123.62, 123.44, 123.39, 121.98.
HRMS (EI+) m/z calcd. for C23H14Br2N2[M]+ : 476.9597, 478.9577, found: 476.9595,
478.9578.
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2-methyl-5,6-diphenylimidazo[2,1-a]isoquinoline (4aa): EtOAc/n-hexane (15%); Yellow
crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.63 (d, J = 8 Hz, 1H), 7.52 (t, J = 8 Hz, 1H),
7.36 (t, J = 8 Hz, 1H), 7.29 (d, J = 8 Hz, 1H), 7.24-7.23 (m, 3H), 7.20 (s, 1H), 7.19-7.18 (m,
2H). 7.18-7.15 (m, 3H), 7.11-7.09 (m , 2H), 2.36 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
141.55, 139.48, 135.06, 132.72, 132.10, 130.48, 129.47, 129.17, 127.71, 127.56, 126.97,
126.58, 126.18, 125.33,
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123.87, 122.78, 122.03, 121.73, 109.83, 13.25. HRMS (EI+) m/z calcd. for C24H18N2[M]+ :
334.1470, found: 334.1472.
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5,6-bis(2-fluorophenyl)-2-methylimidazo[2,1-a]isoquinoline (4ab): EtOAc/n-hexane (12
%); brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.67 (d, J = 8 Hz, 1H), 7.57 (t,J =
8 Hz, 1H), 7.42-7.39 (m, 1H), 7.31-7.28 (m, 1H), 7.23-7.2 (s, 1H), 7.19 (s, 1H), 7.16-7.12 (m,
2H), 7.05-6.99 (m, 3H), 6.97-6.89 (m, 1H), 6.84 (s, 1H), 2.39 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 161.50, 160.98, 159.55, 159.00, 142.64, 140.96, 132.62, 131.79, 131.73, 130.30,
130.24, 129.69, 128.21, 128.13, 125.80, 124.77, 124.74, 124.25, 124.22, 123.27, 122.95,
119.43, 115.97, 115.80, 115.46, 155.28, 110.70, 100.00, 14.41. HRMS (EI+) m/z calcd. for
C24H16F2N2[M]+ : 371.1354, found: 371.1356.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801056
European Journal of Organic Chemistry
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5,6-bis(2-fluorophenyl)-3-methylimidazo[2,1-a]isoquinoline (4ac): EtOAc/n-hexane (15
%); brown crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.74 (d, J = 8 Hz, 1H), 7.64 (t, J =
8 Hz, 1H), 7.49-7.46 (m, 1H), 7.37-7.32 (m, 2H), 7.30-7.28 (m ,2H), 7.21 (t, J = 8 Hz, 1H),
7.13-7.11 (m, 1H), 7.09-7.08 (m, 1H), 7.06-7.02 (m, 2H), 6.84 (s, 1H), 2.46 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 142.59, 14.89, 133.37, 132.61, 132.16, 132.14, 131.80, 131.74, 131.63,
131.57, 131.55, 130.31, 129.70, 128.25, 128.24, 128.17, 125.87, 125.80, 124.78, 124.75,
124.25, 124.22, 123.36, 123.32, 115.98, 115.81, 110.77, 110.70, 14.37. HRMS (EI+) m/z
calcd. for C24H16F2N2[M]+: 371.1354, found: 371.1357.
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6-(4-chlorophenyl)-5-(thiophen-2-yl)imidazo[2,1-a]isoquinoline (4ad): EtOAc/n-hexane (6 %);
yellow crystalline solid, 1H NMR (400 MHz, CDCl3) δ 8.75 (d, J = 8 Hz, 1H), 7.70-7.66 ( m,
1H), 7.61-7.59 (m, 1H), 7.57 (br, s, 1H), 7.55-7.52 (m, 1H), 7.38 (d, J = 8 Hz, 2H), 7.34-7.30
(m, 3H), 7.16 (br, s, 1H), 7.01-6.99 (m, 1H), 6.93-6.92 (m, 1H). 13C NMR (100 MHz, CDCl3)
δ 135.89, 135.36, 133.99, 131.31, 130.93, 130.16, 129.17, 128.60, 128.41, 127.12, 126.89,
126.29, 123.27, 113.84. HRMS (EI+) m/z calcd. for C21H13ClN2S [M]+: 361.0561, found:
361.0578.
439
Acknowledgement
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We acknowledge Shiv Nadar University for the financial support. We thank Mr. Ranajit Das
and Mr. Anil Kumar for helping us with generating the single crystal X-Ray structure of
compounds 4u and v. We also thank Mr. Harsh Bhatia for helping us with the
photoluminescence study.
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Keywords
Annulation, catalysis, cobalt, fluorescence, polyheteroarenes
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