Carbon Nanotube-Ruthenium Hybrids for the Partial Reduction of 2-Nitrochalcones: Easy Access to Quinoline N-Oxides

Article abstract of DOI:10.1002/cctc.201600042

A ruthenium-carbon nanotube nanohybrid was employed as a catalyst in the tandem transformation of nitrochalcones into quinoline N-oxides. Partial reduction of the nitro group to a hydroxylamine, followed by in situ intramolecular condensation to the carbo

Full text of DOI:10.1002/cctc.201600042

DOI: 10.1002/cctc.201600042
Communications
Carbon Nanotube–Ruthenium Hybrids for the Partial
Reduction of 2-Nitrochalcones: Easy Access to Quinoline
N-Oxides
Pallabita Basu,[a] Praveen Prakash,[b] Edmond Gravel,[b] Nimesh Shah,[a] Kalisankar Bera,[a]
Eric Doris,*[b] and Irishi N. N. Namboothiri*[a]
A ruthenium–carbon nanotube nanohybrid was employed as
a catalyst in the tandem transformation of nitrochalcones into
quinoline N-oxides. Partial reduction of the nitro group to a hy-
droxylamine, followed by in situ intramolecular condensation
to the carbonyl afforded the quinoline-N-oxides in satisfactory
to good yields. Reduction of the nitro group was selective and
independent of changes in the reaction conditions. Highlights
of this method include a very low catalyst loading relative to
that required for conventional methods for the synthesis of
quinoline N-oxides and mild reaction conditions.
The reactivity of RhCNTs in the dehydrogenation of N-hetero-
cycles[15] and RuCNTs in the reduction of nitroarenes to arylhy-
droxylamines or arylamines[16] has also been demonstrated.
This manuscript describes another application of the RuCNT
nanohybrid in the selective catalytic reduction of nitrochal-
cones that was applied to the synthesis of quinoline N-oxides.
Quinolines and quinoline N-oxides make up parts of many
naturally occurring compounds and are of biological signifi-
cance.[17–19] In particular, quinoline N-oxides exhibit antitumor[20]
and antimalarial activities.[21] In addition, the quinoline N-oxide
core has been found in drugs that activate microsomal Na/K-
ATPase.[22] The main method for the preparation of quinoline
N-oxides is the oxidation of quinolines.[23] The direct palladium-
catalyzed arylation of quinoline N-oxides to 2-arylquinoline N-
oxides was recently reported.[24–26] Morita–Baylis–Hillman ad-
ducts derived from 2-nitrobenzaldehyde also react in the pres-
ence of trifluoroacetic acid to give N-oxides via a nitroso inter-
mediate.[27] Although there are reports of reduction–cyclization
sequences starting from 2-nitrochalcones and 3-hydroxyke-
tones for the preparation of quinoline N-oxide and its deriva-
tives,[28–31] applicability of such methods is curtailed owing to
the requirement of drastic conditions such as reflux tempera-
tures or excess amounts of metal catalysts. This encouraged us
to develop a simple and convenient method for the synthesis
of quinoline N-oxides under mild conditions of temperature
(room temperature), pressure (atmospheric pressure), and low
catalyst loading. Herein, we report the synthesis of quinoline
N-oxides through the partial reduction of the nitro group of 2-
nitrochalcones by using hydrazine hydrate as the reducing
agent in the presence of RuCNT as the catalyst. The choice of
hydrazine hydrate was governed by the fact that it stands as
a cheap, safe-to-handle, and convenient source of hydrogen
that releases N2 as the only side product. The resulting hydrox-
ylamines undergo spontaneous in situ cyclization to quinoline
N-oxides in a tandem reduction–cyclization sequence.
Carbon nanotubes (CNTs) are attractive platforms for the as-
sembly of metallic catalyst particles in, for example, heteroge-
neous catalysis. We recently contributed to this field and re-
ported an original CNT-based supramolecular multilayered as-
sembly of various metals such as Au, Rh, Pd, and Ru.[1] In com-
parison to colloidal metal nanoparticles and metal nanoparti-
cles on other supports, metal–CNT nanohybrids exhibit
exceptional catalytic activity in various organic transformations.
The superior performances of CNTs as supports have been at-
tributed to their high surface area, chemical inertness, and abil-
ity to stabilize transient higher oxidation states of metals.
Among the abovementioned metal–CNT assemblies, AuCNTs[2]
have found applications in the oxidation of silanes,[3] alcohols,[4]
and phenols;[5] the deoxygenation of amine N-oxides;[6] the re-
ductive amination[7] and N-formylation[8] of aldehydes; and in
the synthesis of heterocycles such as quinoxalines,[9] regardless
of the size of the Au nanoparticles.[10] Gold nanoparticles sup-
ported solely by supramolecular assembly (organic nanotubes,
AuONTs) also exhibit interesting catalytic activity, for instance,
in the oxidative coupling of primary amines to imines[11] and
the oxidation of silanes.[12] Similarly, PdCNTs were shown to be
active in the room-temperature Suzuki coupling of aryl hal-
ides[13] and the Tsuji–Wacker oxidation of terminal olefins.[14]
The RuCNT catalyst was prepared by introducing a supra-
molecular multilayer assembly consisting of an inner polyan-
ionic layer and an outer polycationic layer around CNTs fol-
lowed by anchoring the Ru nanoparticles.[16] At first, CNTs were
sonicated in an aqueous alkaline solution of diacetylene nitrilo-
triacetic amphiphile (DANTA). This formed the first layer in
which the long lipophilic chains of DANTA molecules were
bound to the surface of the CNTs through hydrophobic inter-
actions, whereas the polar heads faced the aqueous medium.
Photopolymerization of the diacetylene moiety at l=254 nm
further strengthened this primary anionic layer. The second
[a] P. Basu, Dr. N. Shah, Dr. K. Bera, Dr. I. N. N. Namboothiri
Department of Chemistry
Indian Institute of Technology Bombay
Mumbai 400076 (India)
E-mail: irishi@chem.iitb.ac.in
[b] Dr. P. Prakash, Dr. E. Gravel, Dr. E. Doris
CEA, iBiTecS, Service de Chimie Bioorganique et de Marquage
91191 Gif-sur-Yvette (France)
E-mail: eric.doris@cea.fr
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cctc.201600042.
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Communications
layer was subsequently introduced by addition of cationic
poly(diallyldimethylammonium chloride) (PDADMAC), which
was immobilized through electrostatic interactions with the
anionic layer. In the final step, preformed ruthenium nanoparti-
cles (RuNPs)[32] were added and stabilized on the CNT supra-
molecular platform upon interaction with the polyammonium
network.
Table 1. Scope of the reaction.[a]
Entry
Ar
2
t
[h]
Yield[b]
[%]
The above RuCNT nanohybrid was characterized by a variety
of techniques. First, transmission electron microscopy (TEM,
Figure 1) confirmed the uniform distribution of RuNPs on the
1
Ph
2a
2b
2c
2d
2e
2 f
2g
2h
2i
4
3
6
2
6
3
2.5
4
3
55
52
78
63
76
35
70
46
50
2
3
4
5
6
7
8
4-MeC6H4
2-MeOC6H4
2-ClC6H4
3,4-Cl2C6H3
3-BrC6H4
4-BrC6H4
4-FC6H4
9
4-NCC6H4
1-naphthyl
2-furyl
benzo-2-furyl
styrenyl
10
11
12
13
2j
2k
2l
2
3
79
75
24
24
trace
mixture
2m
[a] Reaction conditions: nitrochalcone 1 (0.1 mmol), hydrazine hydrate
(2 mmol), RuCNTs (0.4 mol%), RT. [b] Yield of isolated product.
with a variety of 2-nitrochalcones 1 (Table 1). In this context, 2-
nitrochalcones possessing various aryl and heteroaryl groups
that constituted the aroyl moiety were investigated. There was
no appreciable substituent effect on the rate of reaction or
product yield. Chalcones with an unsubstituted phenyl group
(see substrate 1a) and a phenyl group bearing a weakly elec-
tron-donating substituent (see substrate 1b) in the para posi-
tion afforded products 2a and 2b, respectively, in comparable
yet moderate yields (55 and 52%; Table 1, entries 1 and 2). The
yields were higher (70–79%) for chalcones bearing strongly
electron-donating substituents (see substrate 1c; Table 1,
entry 3) and weakly deactivating substituents (see substrates
1e and 1g; Table 1, entries 5 and 7) on the benzene ring as
well as for fused aromatic system 1j (Table 1, entry 10) and
heteroaromatic system 1k (Table 1, entry 11). However, where-
as chalcone 1d bearing a weakly deactivating substituent in
the ortho position furnished product 2d in good yield (63%;
Table 1, entry 4), chalcone 1 f bearing a similar substituent in
the meta position afforded product 2 f only in low yield (35%;
Table 1, entry 6). Finally, if the aryl group was either benzofuran
(1l) or styrenyl (1m), no satisfying result was obtained (Table 1,
entries 12 and 13).
Figure 1. TEM image of the RuCNT catalyst and general scheme of the trans-
formation reported herein.
surface of the CNT bilayer assembly. The RuNP average diame-
ter of approximately 2 nm was established by statistical size
analysis by using the TEM micrographs. The metal concentra-
tion of the RuCNT aqueous suspension was measured to be
3.2 mm by inductively coupled plasma mass spectrometry (ICP-
MS).
Given that Ru is a suitable metal for the catalytic hydrogena-
tion of nitro groups,[33–36] and inspired by our recent results on
the selective reduction of various nitroarenes to the corre-
sponding amines or hydroxylamines,[16] we sought to extend
the methodology to 2-nitrochalcones, which after reduction
were expected to give quinolines or the corresponding N-
oxides by intramolecular cyclization. To this end, we subjected
chalcone 1a to the conditions established earlier. To our de-
light, upon performing the reaction in THF with hydrazine
monohydrate (20 equiv.) and the RuCNTs (0.4 mol%) at room
temperature, quinoline N-oxide 2a was isolated in satisfactory
yield (55%; Table 1, entry 1). The formation of 2a can be ra-
tionalized by partial reduction of the nitro group to the hy-
droxylamine and further condensation and cyclization with the
adjacent carbonyl group. However, we previously reported
that full reduction to arylamines was observed in H2O.[16] We
thus looked at the effect of water in the above transformation.
Interestingly, we did not detect the formation of quinoline
upon adding water (THF/H2O, 1:1) to the mixture, which sug-
gested that the in situ formed hydroxylamine spontaneously
cyclized to quinoline N-oxide 2a without undergoing further
reduction to the amine.
The use of hydrazine in excess in the above experiments
was required, as the reaction remained incomplete with lower
amounts of the hydrogen source (e.g., 5 or 10 equiv.). Recycla-
bility of the catalyst was investigated by performing five con-
secutive reductions/condensations of 1j with the same RuCNT
sample recovered after each cycle by centrifugation (Table 2).
No decrease in the catalytic activity was observed up to the
fifth cycle of the experiment (ꢀ79% yield of 2j in THF
through five cycles of 2 h each). This experiment confirmed
the heterogeneous nature of the reaction and also highlighted
the low cost and the low environmental impact associated
with our methodology. ICP-MS analysis of the recycled reaction
The scope of our nitro group reduction–cyclization cascade
for the synthesis of quinoline N-oxides 2 was then evaluated
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(2 mL) under a nitrogen atmosphere for 2 h. The catalyst was re-
covered by centrifugation, washed with THF, and reused in subse-
quent reactions. In parallel, the solvent was removed in vacuo, and
the residue was purified by column chromatography (silica gel, pe-
troleum ether/EtOAc 3:1) to afford quinoline N-oxide 2j.
Table 2. Recycling experiments with the RuCNT catalyst.[a]
TON and TOF calculation
Entry
RuCNT
Yield[b]
[%]
A mixture of (E)-1-(naphthalen-1-yl)-3-(2-nitrophenyl)prop-2-en-1-
one (1j; 30.3 mg, 0.1 mmol), hydrazine monohydrate (100 mL,
100 mg, 2 mmol, 20 equiv.), and water-free RuCNTs (32 mL from
a 3.2 mm suspension in THF, 0.1 mol%) was stirred in dry THF
(2 mL) under a nitrogen atmosphere for 2 h. The solvent was re-
moved in vacuo, and the residue was purified by column chroma-
tography (silica gel, petroleum ether/EtOAc 3:1) to afford quinoline
N-oxide 2j in 72% yield.
1
2
3
4
5
fresh
79
79
78
79
79
recycle 1
recycle 2
recycle 3
recycle 4
[a] Reaction conditions: nitrochalcone 1j (0.1 mmol), hydrazine hydrate
(2 mmol), RuCNTs (0.4 mol%), RT, 2 h. [b] Yield of isolated product.
mmolproduct 0:072
mmolcatalyst 0:0001
TON for 2 j¼
TOF for 2 j¼
¼
¼ 720
ð1Þ
ð2Þ
mixtures showed no significant amounts of ruthenium that
could have leached out of the CNTs. Also, TEM analysis of the
catalyst after the fifth cycle indicated no major modification of
the carbon nanotube based catalyst. The reaction did not pro-
ceed if it was performed in the absence of the RuCNT catalyst
or in the presence of RuCl3 as the catalyst. In addition, the use
of non-supported RuNPs led to lower yields of the product,
and the catalyst was fully deactivated after the first cycle. The
tandem reduction–cyclization reaction was still operative with
the use of only 0.1 mol% of RuCNTs. Under these conditions,
a turnover number (TON) of 720 and a turnover frequency
(TOF) of 360 hÀ1 were calculated (see the Experimental Section
for details).
TON 720
¼
¼ 360 hÀ1
time
2
Characterization data
2a:[29] Brown solid; yield: 55% (12 mg); m.p. 142–1448C (lit 148–
1
1498C); H NMR (500 MHz, CDCl3): d=7.46–7.49 (m, 1H), 7.51–7.54
(m, 3H), 7.65 (td, J=8.0, 0.9 Hz, 1H), 7.76 (d, J=8.7 Hz, 1H) 7.78–
7.81 (m, 1H), 7.87 (d, J=8.0 Hz, 1H), 7.98 (d, J=8.4 Hz, 2H),
8.86 ppm (d, J=8.7 Hz, 1H); 13C NMR (125 MHz, CDCl3): d=120.5,
123.5, 125.5, 128.1, 128.5, 128.6, 129.3, 129.7, 129.8, 130.8, 133.7,
142.5, 145.3 ppm; HRMS (ESI): m/z: calcd for C15H11NNaO: 244.0733
[M+Na+]; found: 244.0737.
In summary, quinoline N-oxides were synthesized from readi-
ly available 2-nitrochalcones in moderate to good yields under
the catalytic influence of a ruthenium–carbon nanotube nano-
hybrid at room temperature. This one-pot reduction–conden-
sation sequence takes place under mild and sustainable condi-
tions with a very low catalyst loading and is an effective alter-
native to existing methods for the synthesis of biologically im-
portant quinoline N-oxides.
2b:[29] Yellow solid; yield: 52% (12 mg); m.p. 122–1258C (lit 127–
1288C); 1H NMR (400 MHz, CDCl3): d=2.43 (s, 3H), 7.33 (d, J=
8.1 Hz, 2H), 7.51 (d, J=8.8 Hz, 1H), 7.63 (td, J=8.1, 0.9 Hz, 1H),
7.75 (d, J=8.8 Hz, 1H), 7.76 À7.81 (m, 1H), 7.86 (d, J=8.1 Hz, 1H),
7.90 (d, J=8.1 Hz, 2H), 8.85 ppm (d, J=8.8 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=21.6, 120.3, 123.4, 125.3, 128.0, 128.4, 129.1,
129.5, 129.6, 130.6, 130.7, 139.8, 142.4, 145.2 ppm; HRMS (ESI): m/z:
calcd for C16H13NNaO: 258.0889 [M+Na+]; found: 258.0889.
2c:[37] White solid; yield: 78% (20 mg); m.p. 182–1848C; 1H NMR
(400 MHz, CDCl3): d=3.81 (s, 3H), 7.05 (dd, J=8.4, 1.7 Hz, 1H), 7.10
(td, J=8.4, 0.9 Hz, 1H), 7.40 (dd, J=8.4, 0.9 Hz, 1H), 7.46 (td, J=
8.4, 1.7 Hz, 1H), 7.52 (dd, J=8.6, 1.7 Hz, 1H), 7.63 (td, J=8.2,
0.9 Hz, 1H), 7.71 (d, J=8.6 Hz, 1H), 7.75 (td, J=8.7, 1.3 Hz, 1H)
7.87 (d, J=8.2 Hz, 1H), 8.83 ppm (d, J=8.7 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=56.0, 111.6, 120.5, 120.8, 123.2, 124.5, 124.6,
128.1, 128.5, 130.1, 130.3, 130.9, 131.1, 142.3, 144.2, 157.4 ppm;
HRMS (ESI): m/z: calcd for C16H13NNaO2: 274.0838 [M+Na+]; found:
274.0827.
Experimental Section
General procedure for the synthesis of quinoline N-oxides 2
A mixture of 2-nitrochalcone 1 (0.1 mmol, 1 equiv.), hydrazine
monohydrate (100 mL, 100 mg, 2 mmol, 20 equiv.), and water-free
RuCNTs (125 mL from a 3.2 mm suspension in THF, 0.4 mol%) was
stirred in dry THF (2 mL) under a nitrogen atmosphere until the re-
action was complete (monitored by TLC). The solvent was removed
in vacuo, and the residue was purified by column chromatography
(silica gel, petroleum ether/EtOAc 3:1) to afford pure quinoline N-
oxide 2.
1
2d:[24] Yellow sticky liquid; yield: 63% (16 mg); H NMR (400 MHz,
CDCl3): d=7.37–7.45 (m, 3H), 7.51–7.57 (m, 2H), 7.63–7.68 (m, 1H),
7.76–7.81 (m, 2H), 7.91 (d, J=8.0 Hz, 1H), 8.83 ppm (d, J=8.8 Hz,
1H); 13C NMR (125 MHz, CDCl3): d=120.3, 123.7, 124.9, 127.0,
128.2, 128.9, 129.9, 130.2, 130.6, 130.7, 131.1, 133.3, 133.9, 142.1,
144.1 ppm; HRMS (ESI): m/z: calcd for C15H10NClNaO: 278.0343
[M+Na+]; found: 278.0345.
Recycling experiment
A mixture of (E)-1-(naphthalen-1-yl)-3-(2-nitrophenyl)prop-2-en-1-
one (1j; 30.3 mg, 0.1 mmol, 1 equiv.), hydrazine monohydrate
(100 mL, 100 mg, 2 mmol, 20 equiv.), and water-free RuCNTs (125 mL
from a 3.2 mm suspension in THF, 0.4 mol%) was stirred in dry THF
2e: White solid; yield: 76% (22 mg); m.p. 83–858C; 1H NMR
(400 MHz, CDCl3): d=7.36 (d, J=8.6 Hz, 1H), 7.40 (d, J=8.1 Hz,
1H), 7.48 (d, J=8.2 Hz, 1H), 7.57 (s, 1H), 7.68 (t, J=7.5 Hz, 1H),
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7.77 (d, J=8.2 Hz, 1H), 7.80 (merged t, J=7.5 Hz, 1H), 7.90 (d, J=
8.1 Hz, 1H), 8.81 ppm (d, J=8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d=120.4, 123.6, 124.9, 127.5, 128.3, 129.1, 130.0, 130.4, 130.9,
131.8, 132.1, 134.9, 136.2, 142.2, 143.1 ppm; IR (neat): n˜ =2994 (w),
1587 (w), 1563 (w), 1479 (m), 1345 (s), 1216 (s), 755 cmÀ1 (vs);
HRMS (ESI): m/z: calcd for C15H10NCl2O: 290.0134 [M+H+]; found:
290.0137.
Acknowledgements
Supports from the Indo-French Centre for the Promotion of Ad-
vanced Research (IFCPAR)/Centre Franco-Indien pour la Promo-
tion de la Recherche AvancØe (CEFIPRA) and the Enhanced Euro-
talent program are gratefully acknowledged (Project no. 4705-1).
The TEM-team platform (CEA, iBiTec-S) is acknowledged for help
with TEM images. The “Service de Chimie Bioorganique et de
Marquage” belongs to the Laboratory of Excellence in Research
on Medication and Innovative Therapeutics (ANR-10-LABX-0033-
LERMIT).
2 f: Brown solid; yield: 35% (10 mg); m.p. 138–1408C; 1H NMR
(500 MHz, CDCl3): d=7.40 (t, J=7.9 Hz, 1H), 7.48 (d, J=8.7 Hz, 1H),
7.60 (dq, J=7.9, 1.1 Hz, 1H), 7.67 (td, J=8.1, 1.1 Hz, 1H), 7.77 (d,
J=8.7 Hz, 1H), 7.81 (td, J=8.6, 1.5 Hz, 1H), 7.88–7.91 (m, 2H), 8.15
(t, J=1.5 Hz, 1H), 8.83 ppm (d, J=8.7 Hz, 1H); 13C NMR (125 MHz,
CDCl3): d=120.5, 122.5, 123.2, 125.7, 128.2, 128.4, 129.0, 129.9,
130.0, 131.0, 132.7, 132.8, 135.5, 142.4, 143.8 ppm; IR (neat): n˜ =
3068 (w), 1566 (m), 1448 (w), 1336 (s), 1242 (m), 818 cmÀ1 (m);
HRMS (ESI): m/z: calcd for C15H10NBrNaO: 321.9838 [M+Na+];
found: 321.9836.
Keywords: heterogeneous catalysis
nanotubes · ruthenium · sustainable chemistry
·
nanoparticles
·
2g: Yellow solid; yield: 70% (21 mg); m.p. 172–1748C; 1H NMR
(400 MHz, CDCl3): d=7.48 (d, J=8.7 Hz, 1H), 7.65 (d, J=8.6 Hz, 1H)
7.64–7.67 (m, merged with doublet, 2H), 7.76 (d, J=8.7 Hz, 1H),
7.80 (td, merged with doublet, J=8.6, 1.3 Hz, 1H), 7.86–7.89 (m,
2H), 7.88 (d, J=8.6 Hz, 1H), 8.83 ppm (d, J=8.7 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=120.4, 123.0, 124.1, 125.6, 128.2, 128.8, 129.8,
131.0, 131.4, 131.7, 132.5, 142.5, 144.1 ppm; IR (neat): n˜ =3056 (w),
1338 (s), 1325 (m), 807 cmÀ1 (vs); HRMS (ESI): m/z: calcd for
C15H10NBrNaO: 321.9838 [M+Na+]; found: 321.9835.
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2h:[25] Yellow solid; yield: 46% (11 mg); m.p. 158–1608C (lit 161–
1
1638C); H NMR (500 MHz, CDCl3): d=7.21 (t, J=8.6 Hz, 2H), 7.49
(d, J=8.7 Hz, 1H), 7.64–7.67 (m, 1H), 7.78 (d, J=8.6 Hz, 1H), 7.78–
7.82 (m, 1H), 7.87 (d, J=8.1 Hz, 1H), 7.99–8.02 (m, 2H), 8.84 ppm
(d, J=8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=115.4 (d, J=
22.0 Hz), 120.2, 123.0, 125.6, 125.7, 128.0, 128.6, 129.5 (d, J=
19.0 Hz), 130.8, 131.8 (d, J=8.0 Hz), 142.3, 144.2, 163.3 ppm (d, J=
249.0 Hz); HRMS (ESI): m/z: calcd for C15H10NONaF: 262.0639
[M+Na+]; found: 262.0636.
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2i:[26] Yellowish brown solid; yield: 50% (12 mg); m.p. 204–2068C
(lit 206–2088C); 1H NMR (400 MHz, CDCl3): d=7.50 (d, J=8.4 Hz,
1H), 7.70 (t, J=7.3 Hz, 1H), 7.80–7.85 (m, 4H), 7.91 (d, J=8.0 Hz,
1H), 8.11 (d, J=8.0 Hz, 2H), 8.82 ppm (d, J=8.8 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d=113.3, 118.6, 120.4, 122.9, 126.5, 128.4, 129.4,
130.1, 130.6, 131.5, 132.3, 137.9, 142.4, 143.6 ppm; HRMS (ESI): m/z:
calcd for C16H10N2NaO: 269.0685 [M+Na+]; found: 269.0689.
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2j:[29] Brownish white solid; yield: 79% (21 mg); m.p. 164–1688C
(lit 168–1698C); 1H NMR (400 MHz, CDCl3): d=7.42–7.54 (m, 4H),
7.60–7.63 (m, 2H), 7.70 (t, J=7.6 Hz, 1H), 7.80–7.84 (m, 2H), 7.94
(dd, J=7.6, 3.6 Hz, 2H), 8.00 (dd, J=6.0, 3.6 Hz, 1H), 8.88 ppm (d,
J=8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=120.6, 124.7, 125.0,
125.5, 125.6, 126.4, 127.0, 127.9, 128.3, 128.8, 128.8, 130.2, 130.3,
130.8, 131.0, 132.3, 133.7, 142.4, 145.9 ppm; HRMS (ESI): m/z: calcd
for C19H14NO: 272.1070 [M+H+]; found: 272.1065.
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2k: Yellow solid; yield: 75% (12 mg); m.p. 95–978C; 1H NMR
(400 MHz, CDCl3): d=6.69 (dd, J=3.4, 1.7 Hz, 1H), 7.61 (t, J=
7.8 Hz, 1H), 7.67 (d, J=1.7 Hz, 1H), 7.73–7.80 (m, 2H), 7.84 (d, J=
7.8 Hz, 1H), 8.03 (d, J=8.9 Hz, 1H), 8.27 (d, J=3.4 Hz, 1H),
8.81 ppm (d, J=8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3): d=112.9,
117.5, 118.9, 119.7, 125.3, 128.1, 128.2, 128.5, 130.7, 136.7, 142.2,
144.4, 146.2 ppm; IR (neat): n˜ =2927 (w), 1617 (m), 1602 (m), 1571
(m), 1510 (m), 1347 (s), 1248 (s), 1013 (s), 810 (s), 745 cmÀ1 (vs);
HRMS (ESI): m/z: calcd for C13H10NO2: 212.0706 [M+H+]; found:
212.0700.
ChemCatChem 2016, 8, 1298 – 1302
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: January 13, 2016
Revised: February 11, 2016
Published online on March 10, 2016
ChemCatChem 2016, 8, 1298 – 1302
www.chemcatchem.org
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim