Transition-Metal-Free Approach for the Synthesis of 4-Aryl-quinolines from Alkynes and Anilines

Article abstract of DOI:10.1021/acs.joc.8b01204

An efficient and transition-metal-free approach for the synthesis of 4-arylquinolines from readily available anilines and alkynes in the presence of K₂S₂O₈ and DMSO has been developed. A variety of alkynes and anilines having a diverse range of substitution patterns can undergo the one-pot cascade process successfully. Effectively, this method uses DMSO as one carbon source, thus providing a highly atom-economical and environmentally benign approach for the synthesis of 4-arylquinolines.

Full text of DOI:10.1021/acs.joc.8b01204

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Article
Transition Metal Free Approach for the Synthesis
of 4-Aryl-quinolines from Alkynes and Anilines
Mandalaparthi Phanindrudu, Sandip Balasaheb Wakade, Dipak
Kumar Tiwari, Pravin R. Likhar, and Dharmendra Kumar Tiwari
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01204 • Publication Date (Web): 03 Jul 2018
Downloaded from http://pubs.acs.org on July 4, 2018
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The Journal of Organic Chemistry
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Transition Metal Free Approach for the Synthesis of 4-Aryl-
quinolines from Alkynes and Anilines
Mandalaparthi Phanindrudu,†,‡ Sandip Balasaheb Wakade,†,‡ Dipak Kumar Tiwari,†,‡ Pravin R. Likhar,‡,
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§, and Dharmendra Kumar Tiwari*,†,‡
†Division of Organic Synthesis and Process Chemistry, CSIRꢀIndian Institute of Chemical Technology, Hyderabad 500007,
India.
§ Inorganic and Physical Chemistry Division, CSIRꢀIndian Institute of Chemical Technology, Hyderabad 500007, India.
‡Academy of Scientific & Innovative Research (AcSIR), New Delhi, 110001, India.
ABSTRACT: An efficient and transition metalꢀfree approach for
the synthesis of 4ꢀarylquinolines from readily available anilines and
R1
Metal
alkynes in the presence of K2S2O8 and DMSO has been developed.
A variety of alkynes and anilines having diverse range of substituꢀ
tion patterns can undergo the one pot cascade process successfully.
Effectively, this method uses DMSO as one carbon source, thus
providing a highly atom economical and environmentally benign
approach for the synthesis of 4ꢀarylquinolines.
R2
R1
+
R2
O
S
H2N
N
DMSO as one carbon source
Transition metal free
•
•
•
One C-N and two C-C bond formation
•
Broad substrate scope
(a) Previous work: Transition metal catalyzed
INTRODUCTION
Ar
Quinoline is one of the most prevalent nitrogenꢀcontaining
motifs frequently found in various natural products and FDAꢀ
approved pharmaceuticals (Fig.ꢀ1, A-E).1 In particular, 4ꢀ
arylquinoline scaffolds are an integral part of various mediciꢀ
nally important compounds displaying a wide range of biologꢀ
ical activities such as antiꢀthyroid cancer, antifungal, analgeꢀ
sic, antimalarial, antibacterial, antiꢀinflammatory, antiasthmatꢀ
ic, antiproliferative activity, ALK5 and PI3K inhibitory propꢀ
erties (Fig ꢀ1, BꢀE).1ꢀ2 This key heterocyclic core exhibits
common pharmacophoric and chelating properties, as a result
of which it has found broad applications in both, drug designꢀ
ing, as well as material sciences.3
Cp*[Co(CO)I2
]
H2N
+
Ar
AgNTf2, K2S2O8
DMSO
N
(b) This work:Transition metal free: Alkynes and Anilines
Ar
K2S2O8
Ar
H2N
+
DMSO
N
Transition metal free; In-situ generation of Imine from anilne and DMSO
DMSO as one carbon source and solvent
Broad substrate scope
Scheme 1. Strategies for the synthesis of 4-arylquinolines from alkynes and
amines.
transition metal catalyzed CꢀH functionalization is considered
to be one of the most attractive, reliable, and atom economical
method for the synthesis of 4ꢀsubstituted quinolines.5 In this
regard very recently Yi and coꢀworkers have developed a
Co(III)ꢀcatalyzed C−H activation strategy for the oneꢀpot tanꢀ
dem synthesis of 4ꢀ arylquinolines from aryl methyl ketones
and aryl amines using paraformaldehyde as the carbonyl surꢀ
rogate.6a In yet another report, Singh and coꢀworkers develꢀ
oped an elegant iron catalyzed synthesis of 4ꢀarylquinolines
from aryl methyl ketones and anilines via K2S2O8 promoted
oxidative annulation.6b Very recently, Yi and coꢀworkers disꢀ
closed the Co(III)ꢀcatalyzed and DMSOꢀinvolved CꢀH activaꢀ
tion/cyclization of amines and alkynes to prepare 4ꢀ
arylquinolines.7 In this transformation, authors reported that
the two different additives such as AgNTf2 and K2S2O8 are
essential to facilitate this reaction (Schemeꢀ1a). Although all
these transition metal catalyzed approaches allow a convenient
access to 4ꢀarylquinolines, the use of expensive and toxic tranꢀ
sition metal catalysts and additives are major drawbacks assoꢀ
H
H
N
N
O
O
O
F
Br
O
O
HO
N
N
A
B
N
anti-thyroid cancer
TMC-207; BQ
N
HN
N
N
O
HN
S
N
N
N
D
PI3K inhibitor
N
N
O
C
E
ALK5 inhibitor
Antiproliferative activity
Figure 1. Biologically active molecules containing substituted quinolines.
Owing to the immense pharmacological activity, the synthesis
of quinoline and its derivatives has seen extensive research
over the years. 4 Amongst all the reported protocols, the
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ciated with them. Therefore, developing more efficient, ecoꢀ
Page 2 of 8
when the mixture was heated at 60 °C for 12 h under a nitroꢀ
gen atmosphere (entryꢀ2). At this stage, the structure of 3aa
was well characterized using different spectroscopic techꢀ
niques and the spectral data of 3aa was exactly matching with
previously reported compounds. To our delight, a higher yield
(79%) of the desired 3aa was obtained when reaction mixture
was heated at 120 °C (entryꢀ3). However, further raising the
reaction temperature (140 °C), furnished slightly lower yield
of desired 3aa (entryꢀ4). Increasing or decreasing the amount
of oxidant significantly reduced the yield of desired 3aa (enꢀ
tries 5ꢀ6). In order to improve the yields of the desired 3aa,
various oxidants such as (NH4)2S2O8, KHSO4, TBHP, and
TEMPO were screened. Unfortunately, no better results were
obtained (entries 7ꢀ10). Thereafter, several solvents such as
DMF, DMA, and NMP were investigated as one carbon
source,10 of which no better result was obtained (entries 11ꢀ
13). In further efforts to optimize the yield of desired 3aa,
reactions were conducted under air and oxygen atmosphere,
however under both the conditions inferior yields of desired
3aa was obtained (entries 14ꢀ15).
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2
3
4
5
6
7
8
friendly and transition metal free synthesis of 4ꢀarylquinolines
from readily available starting materials is highly desirable
and presents an urgent need.
As a part of our continuing research interest in pharmaceutiꢀ
cally important heterocyclic frameworks,8 we recently develꢀ
oped two new protocols i.e. transition metal catalyzed as well
as transition metalꢀfree synthesis of 3ꢀketoꢀquinolines from
readily available starting materials.9 In continuation of the
same research programme, herein we present an atomꢀ
economical and transition metal free synthesis of 4ꢀ
arylquinolines from readily available aryl amines and alkynes
in the presence of K2S2O8 and DMSO.
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RESULT AND DISCUSSION
At the outset of this investigation, we explored the cascade
reaction of phenyl acetylene (1a) and pꢀtoluidine (2a) using
DMSO as the solvent and the details are summarized in Ta-
bleꢀ1. Our initial efforts by reacting phenyl acetylene (1a, 1.0
mmol) and pꢀtoluidine (1.2 mmol) in the presence of
K2S2O8 (2.5 equiv) in DMSO (3.0 mL) at room temperature
under nitrogen condition was unsuccessful (Table-1, entry 1).
Gratifyingly, a 15% yield of aimed product 3aa was obtained
After having the optimized reaction conditions (Tableꢀ1, enꢀ
try 3) in hand, the substrate scope of the reaction with respect
to various alkynes and anilines was evaluated. As shown in
Table- 2, a wide range of alkynes (1a-1r) and anilines (2b-2g)
effectively participated in this oneꢀpot tandem reaction and
furnished the desired products in moderate to good yields.
Table 2. Substrate scope with different alkynes
Table 1. Optimization of reaction conditionsa
Ph
H2N
Additives
+
Ph
temperature
Solvents
N
C5H11
1a
2a
Additive
3aa
Entry
Temp/[°C
]
Solvent
Yieldsb
(2.5 equiv.)
1
2
K2S2O8
rt
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
n.o.
15%
79%
61%
N
N
N
N
N
3aa; 79%
3ba; 81%
3ca; 77%
3da; 72%
3ea; 72%
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
(NH4)2S2O8
KHSO4
TBHP
60
OMe
F
Cl
Br
3
120
140
120
120
120
120
120
120
120
120
120
120
120
4
c
N
N
N
N
N
5
41%
3fa; 71%
3ga; 69%
3ha; 66%
3ia; 73%
3ja; 68%
NO2
I
CN
d
6
25%
F3C
7
17%
trace
trace
trace
12%
trace
trace
8
N
N
N
N
N
3ka; 75%
3la; 74%
3ma; 70%
3na; 67%
3oa; 68%
9
S
10
11
12
13
14
15
TEMPO
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
N
Different
anilines
N
N
N
N
N
DMA
3sa; 0%
3pa; 71%
3qa; 62%
3ra; 61%
3bb; 77%
NMP
e
O
DMSO
DMSO
40%
Cl
f
37%
N
N
N
N
N
3bf; 74%
OMe
3bg; 69% OMe
aReaction was performed using 1a (1.0 mmol), 2a (1.2 mmol), DMSO (2.0
3bc; 72%
3bd; 72%
3be; 70%
b
mL) and additive (2.5 mmol) under nitrogen atmosphere for 12 h. isolated
yield; c when 3.5 equiv. of K2S2O8 was used; d when 1.5 equiv. of K2S2O8 was
used; e under air; f under O2; n.o = not observed
Reaction conditions: Aryl alkynes (1a-1r; 1.0 mmol), anilines (2a-2g; 1.2
mmol), DMSO (3.0 mL) and K2S2O8 (2.5 mmol) under N2 at 120 °C for 12 h.
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The Journal of Organic Chemistry
Generally, the reaction proceeded smoothly under the standard that led to the formation of 3aa in 38% yield along with thioꢀ
1
2
3
4
5
6
7
8
conditions with various terminal alkynes bearing both elecꢀ
tron donating (1b-1g) and electron withdrawing (1h-1n)
groups at a different position of aryl ring and readily furnished
the corresponding 4ꢀarylquinolines (3aa-3na) in good to modꢀ
erate yields. Aryl alkynes with various substituent’s on the
aromatic ring such as alkyl (1b-1f), tertꢀbutyl (1e), methoxy
(1g), fluoro (1h), chloro (1i), bromo (1j) and iodo (1k) were
tested under the standard conditions and the corresponding
products were obtained in good yields. Substrates with strong
electronꢀwithdrawing groups such as nitro (ꢀNO2; 1l), cyano (ꢀ
CN; 1m) and CF3 (1n) were also tolerated, leading to the deꢀ
sired products in good yields. Furthermore, the polycyclic
aromatic alkynes smoothly underwent this one pot tandem
reaction to furnish desired products (3oa & 3pa) in good
yields. Furthermore, the heteroaryl alkynes such as 2ꢀ
ethynylthiophene (1q) and 2ꢀethynylpyridine (1r) were also
found to be compatible under present condition and furnished
the desired products (3qa & 3ra) in very good yields. Aliphatꢀ
ic alkyne (1ꢀhexyne, 1sa) was also employed in this reaction
under the standard condition, unfortunately, no desired prodꢀ
uct was detected. The substrate scope of the present methodolꢀ
ogy was further extended to various substituted anilines (2b-
2g). Anilines bearing both electron donating (2b-2d) group as
well as electron withdrawing group (2e) worked well in this
cascade reaction and afforded the aimed products (3bb-3bd
and 3be) in good yields. Polycyclic anilines (2f & 2g) also
effectively reacted with alkyne (1b) to furnish the desired
products in moderate to good yields.
phenol as
Scheme-3. Mechanistic Insights
Ph
O
S
without
K2S2O8
Ph
H2N
H2N
+
+
+
+
(1)
(2)
N
2a
2a
1a
1a
3aa; 0%
Ph
O
standard
condition
Ph
S
Ph
N
9
3aa; 38%
10
11
12
13
14
15
16
17
18
19
20
21
22
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60
Ph
O
standard
condition
Ph
H2N
+
Ph
+
S
(3)
(4)
Ph
N
3aa; 0%
1a
O
2a
2a
2a
Ph
O
standard
condition
H2N
H2N
+
+
+
S
Ph
N
F
3aa;31%
Ph
O
Ph
+
D3C
standard
condition
S
(5)
CD3
D
N
100% D
1a
3aa-d2 62%
side product. On the other hand, no product (3aa) formation
was observed when the reaction was performed in diphenyl
sulfoxide solvent. These experiments suggest that DMSO
serves as a carbon source in this reaction. In order to check
another possible route for the formation of 3aa, the acetopheꢀ
none (5) was treated with aniline (2a) under standard reaction
conditions, furnishes the desired 3aa in 31% yield. It indicates
that reaction may also go through arylmethyl ketones generatꢀ
ed in situ from aryl alkynes in the presence of oxidant. To
shed more light on the reaction mechanism, a deuteriumꢀ
labeling experiment was conducted by treating 1a with 2a in
DMSOꢀd6 under standard reaction conditions, which furnished
the desired 3aa-d2 in 62% yield. 1H NMR analysis revealed
100% deuteration at the Cꢀ2 position of 3aa.
The synthetic potential of quinolines thus obtained is illustratꢀ
ed in Scheme 2. The quinolines (3ca & 3ia) were treated with
mꢀCPBA in chloroform at room temperature under air to give
to quinoline NꢀOxides (4 & 7) in 90 and 88% yields respecꢀ
tively. The intermediate 4 was then subjected to amidation
reaction with Nꢀmorpholine in the presence of catalytic
Cu(OAc)2 and Ag2CO3 (2.0 equiv) to give to medicinally valuꢀ
able 4ꢀarylꢀ2ꢀmorpholinoquinoline (6)11 in 88% yield. On the
other hand, the intermediate 7 was then treated with sodium
sulfinate (8) in the presence of I2/TBHP to furnish 4ꢀarylꢀ2ꢀ
tosylquinoline (9) in very good yield via oneꢀpot deoxygenaꢀ
tion and direct sulfonylation.12
Based on the above preliminary experimental results and the
previous literature reports the formation of 4ꢀaryl quinolines
may be explained by two pathways (Scheme 4). The reaction
process may begin with the generation of the sulfenium ion
Scheme 2. Synthetic utility
Scheme 4. Proposed reaction pathways
Et
Et
Et
O
K2S2O8
H
N
2a
Cu(OAc)2 (10 mol%)
Ag2CO3 (2 equiv)
N
S
S
m-CPBA
S
N
H
+
benzene,
120 °C, 24 h
CHCl3, 12 h
KHSO5
A
B
C
N
N
O
Cl
O
5
N
O
Cl
N
4,
6, 88%
3ca
90%
O
………………………………………………………………
Cl
SO2Na
I2, (1.1 equiv)
aq. TBHP (3.3 equiv)
m-CPBA
+
CHCl3, 12 h
DMF, rt
N
N
O
N
Ts
9, 82%
3ia
7,
89%
8
In order to further understand the reaction mechanism, we
carried out a series of control experiments (Scheme 3). When
the reaction was performed without K2S2O8, no product forꢀ
mation was observed which indicates that oxidant is essential
for this reaction. In order to verify the carbon source, we carꢀ
ried out the reaction in the methyl phenyl sulfoxide solvent
3
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broad singlet; coupling constants are reported in Hz. Low
Page 4 of 8
R
1
2
3
4
5
6
7
8
(MS) and high (HRMS) resolution mass spectra were recorded
on a Waters 2695 and Thermo Scientific Exactive spectromeꢀ
ter respectively and mass/charge (m/z) ratios are reported as
values in atomic mass units.
O
F
N
R
F'
2a
c
R
N
-O
N
Representative Procedure for the synthesis of 4-
phenylquinolines (3aa):6b
O
F
R
Path-I
R
Path-II
To a solution of alkyne 1a (0.11 mL, 1.0 mmol) and toluidine
2a (0.13 mL, 1.2 mmol) in DMSO (3.0 mL) was added
K2S2O8 (0.68 gm, 2.5 mmol) at room temperature under nitroꢀ
gen atmosphere. The temperature of oil bath was increased up
to 120 °C.; and mixture was stirred at same temperature for
another 12 h. After completion of reaction (confirmed by
TLC), the reaction mixture was then allowed to attain room
temperature and diluted with ethyl acetate (60 mL). The orꢀ
ganic layer was washed with water (20 mL), sodium bicarꢀ
bonate (20 mL) and brine (20 mL). The organic layer was
further dried over anhydrous sodium sulphate and solvent was
evaporated under reduced pressure to get crude product which
was purified by column chromatography using a mixture of
ethyl acetate/petroleum ether (15%) on silica gel to provide
the desired product 3aa as a white solid (173 mg, 79%). mp
120 ꢀ 123 °C.; 1H NMR (400 MHz, Chloroformꢀd) δ 8.87 (d, J
= 4.4 Hz, 1H), 8.09 (d, J = 8.6 Hz, 1H), 7.66 (s, 1H), 7.58 ꢀ
7.47 (m, 6H), 7.29 (d, J = 4.4 Hz, 1H), 2.46 (s, 3H); 13C NMR
(100 MHz, Chloroformꢀd) δ 148.8, 147.9, 146.9, 138.08,
136.6, 131.6, 129.4, 129.2, 128.5, 128.2, 126.7, 124.5, 121.3,
77.3, 77.0, 76.7, 21.8.
H
D
R
[1,3]-H
shift
N
H
N
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
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60
OH
G
H
N
R
R
E
a) [1,3]-H shift
b) -H2O
R
[O]
c) [O]
3aa
(A) from DMSO in the presence of K2S2O8.7
The sulfenium ion (A) reacts with aniline to form intermediate
B, which undergoes to demethylthiolation9c to form the iminiꢀ
um intermediate C. In pathway I, the iminium intermediꢀ
ate C reacts with alkyne (2a) in DielsꢀAlder fashion to give
intermediate D, which undergoes to 1,3ꢀhydrogen shift to
form E, which upon autoꢀoxidation leads to the formation of
the desired 3aa.13 In another pathway, alkyne (2a) may be
getting oxidized to form acetophenone (F), which subsequentꢀ
ly enolizes to give intermediate F’. This intermediate F’ then
undergoes to nucleophilic attack on iminium intermediꢀ
ate C, followed by cyclization, leading to the formation of
intermediate G. This intermediate G then rearranges to final
product 3aa through 1,3 hydrogen shift, followed by dehydraꢀ
tion and autoꢀoxidation steps.6b
6-methyl-4-(p-tolyl)quinoline (3ba).6b Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3ba as a yellow semi solid (189 mg, 81%). 1H
NMR (400 MHz, Chloroformꢀd) δ 8.85 (d, J = 4.4 Hz, 1H),
8.08 (d, J = 8.6 Hz, 1H), 7.69 (s, 1H), 7.55 (dd, J = 8.6, 1.8
Hz, 1H), 7.40 (d, J = 8.1 Hz, 2H), 7.34 (d, J = 8.0 Hz, 2H),
7.28 (d, J = 4.4 Hz, 1H), 2.47 (s, 3H), 2.47 (s, 3H); 13C NMR
(100 MHz, Chloroformꢀd) δ 148.7, 148.1, 146.9, 138.3, 136.5,
135.2, 131.6, 129.4, 129.3, 129.2, 126.8, 124.6, 121.3, 21.8,
21.3; HRMS (ESI) m/z: [M + H]+ calcd for C17H16N 234.1277;
Found 234.1284.
CONCLUSION
In conclusion, an atomꢀeconomical and transition metal free,
three component reactions cascade have been developed for
the synthesis of 4ꢀarylquinolines from the readily available
alkynes, anilines and DMSO in the presence of K2S2O8. The
reaction worked well with various substituted alkynes and
anilines. As a result, a number of 4ꢀsubstituted quinolines
were synthesized, reflecting the generality of this method. The
synthetic utility of current methodology was further extended
to the synthesis of medicinally important 4ꢀarylꢀ2ꢀ
morpholinoquinoline and 4ꢀarylꢀ2ꢀtosylquinoline.
4-(4-ethylphenyl)-6-methylquinoline (3ca). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
1
86/14) to afford 3ca as a yellow liquid (190 mg, 77%). H
NMR (400 MHz, Chloroformꢀd) δ 8.87 (s, 1H), 8.11 (d, J =
8.6 Hz, 1H), 7.72 (s, 1H), 7.56 (dd, J = 8.6, 1.5 Hz, 1H), 7.42
(d, J = 8.0 Hz, 2H), 7.37 (d, J = 8.0 Hz, 2H), 7.30 (d, J = 4.4
Hz, 1H), 2.77 (q, J = 7.6 Hz, 2H), 2.47 (s, 3H), 1.34 (t, J = 7.6
Hz, 3H); 13C NMR (125 MHz, Chloroformꢀd) δ 148.5, 146.6,
144.6, 136.6, 135.3, 131.7, 129.4, 128.9, 128.1, 126.8, 124.6,
121.4, 28.6, 21.8, 15.4; HRMS (ESI) m/z: [M + H]+ calcd for
C18H18N 248.1424; Found 248.1433.
EXPERIMENTAL SECTION
General Information. All reagents were purchased from
Sigma Aldrich, Alfa Aesar and TCI were used without further
purification. All experiments were carried out under nitrogen
atmosphere. All the solvents used for the reaction were disꢀ
tilled before use. The product purification by column chromaꢀ
tography was accomplished using silica gel 100 ꢀ 200 mesh.
Analytical TLC was performed with Merck silica gel 60 F254
6-methyl-4-(4-pentylphenyl)quinoline (3da). Purified by colꢀ
umn chromatography on silica gel (petroleum ether/ethyl aceꢀ
tate = 86/14) to afford 3da as a white semi solid (208 mg,
72%). 1H NMR (500 MHz, Chloroformꢀd) δ = 8.86 (d, J = 4.4
Hz, 1H), 8.08 (d, J = 8.6 Hz, 1H), 7.71 (s, 1H), 7.56 (dd, J =
8.6, 1.9 Hz, 1H), 7.44 ꢀ 7.41 (m, 2H), 7.35 (d, J = 8.1 Hz, 2H),
7.30 (d, J = 4.4 Hz, 1H), 2.72 (t, J = 7.9 Hz, 2H), 2.48 (s, 3H),
1.75 ꢀ 1.65 (m, 2H), 1.43 ꢀ 1.39 (m, 4H), 0.94 (t, , J = 7.0 Hz,
3H); 13C NMR (125 MHz, Chloroformꢀd) δ = 13C NMR (101
MHz, Chloroformꢀd) δ 148.8, 148.1, 147.0, 143.3, 136.5,
1
plates, and the products were visualized by UV detection. H
and 13C NMR spectra were recorded with 300, 400 and 500
MHz NMR instruments with tertramethylsilane (TMS) as an
internal standard. Highꢀresolution mass spectra (ESIꢀHRMS)
were recorded on ESIꢀQTOP mass spectrometer. Chemical
shifts (δ =) are reported in ppm using TMS as an internal
standard, and spin ꢀspin coupling constants (J) are given in Hz.
1
Multiplicities in the H NMR spectra are described as: s =
singlet, d = doublet, t = triplet, q = quartet, m = multiplet, bs =
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The Journal of Organic Chemistry
135.4, 131.6, 129.4, 129.2, 128.6, 126.8, 124.7, 121.4, 114.0,
(m, 2H), 7.59 (d, J = 8.9 Hz, 2H), 7.38 ꢀ 7.35 (m, 2H), 7.29 (d,
J = 4.4 Hz, 1H), 2.48 (s, 3H); 13C NMR (100 MHz, Chloroꢀ
formꢀd) δ 148.3, 147.3, 146.4, 137.2, 136.8, 132.1, 131.8,
131.0, 128.9, 126.4, 124.2, 122.9, 121.2, 21.8.
35.8, 31.6, 29.7, 22.6, 21.8, 14.1; HRMS (ESI) m/z: [M + H]+
calcd for C21H24N 290.1891; Found 290.19033.
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4-(4-(tert-butyl)phenyl)-6-methylquinoline (3ea). Purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate = 85/15) to afford 3ea as a yellow liquid (198 mg,
4-(4-iodophenyl)-6-methylquinoline (3ka). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3ka as a white solid (258 mg, 75%). mp = 140
ꢀ 146 °C. 1H NMR (500 MHz, Chloroformꢀd) δ = 8.90 (s, 1H),
8.27 (d, J = 8.9 Hz, 1H), 7.91 (d, J = 8.2 Hz, 2H), 7.69 ꢀ 7.63
(m, 2H), 7.38 (d, J = 4.4 Hz, 1H), 7.31 ꢀ 7.25 (m, 2H), 2.51 (s,
3H); 13C NMR (100 MHz, Chloroformꢀd) δ 149.1, 146.9,
144.7, 138.0, 137.9, 136.9, 133.0, 131.2, 127.7, 126.5, 124.4,
121.1, 95.1, 21.9; HRMS (ESI) m/z: [M + H]+ calcd for
C16H13NI 346.0087; Found 346.0077.
1
72%). H NMR (400 MHz, Chloroformꢀd) δ 8.86 (d, J = 4.4
Hz, 1H), 8.07 (d, J = 8.6 Hz, 1H), 7.74 (s, 1H), 7.57 ꢀ 7.54 (m,
3H), 7.47 ꢀ 7.43 (m, 2H), 7.29 (d, J = 4.4 Hz, 1H), 2.49 (s,
3H), 1.42 (s, 9H); 13C NMR (100 MHz, Chloroformꢀd) δ
151.4, 148.9, 147.9, 147.1, 136.4, 135.2, 131.6, 129.9, 129.4,
129.2, 126.8, 125.5, 124.7, 121.4, 34.7, 31.4, 21.8; HRMS
(ESI) m/z: [M + H]+ calcd for C20H22N 276.1736; Found
276.1747.
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4-(3,4-dimethylphenyl)-6-methylquinoline (3fa). Purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate = 88/12) to afford 3fa as a white solid (175 mg, 71%).
mp = 266 ꢀ 268 °C. 1H NMR (500 MHz, Chloroformꢀd) δ 8.89
(s, 1H), 8.64 (d, J = 8.4 Hz, 1H), 7.88 (s, 1H), 7.80 (d, J = 8.3
Hz, 1H), 7.62 (s, 1H), 7.38 (d, J = 7.5 Hz, 1H), 7.34 ꢀ 7.27 (m,
2H), 2.56 (s, 3H), 2.42 (s, 3H), 2.40 (s, 3H); 13C NMR (125
MHz, Chloroformꢀd) δ 155.9, 142.5, 139.8, 139.6, 139.1,
137.7, 135.3, 133.5, 130.5, 130.3, 127.3, 127.0, 125.4, 123.8,
121.2, 22.0, 19.9, 19.7; HRMS (ESI) m/z: [M + H]+ calcd for
C18H18N 248.1422; Found 248.1434.
6-methyl-4-(4-nitrophenyl)quinoline (3la). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
83/17) to afford 3la as a yellow solid (194 mg, 74%). mp =
218 ꢀ 221 °C. 1H NMR (400 MHz, Chloroformꢀd) δ 8.93 (d, J
= 4.4 Hz, 1H), 8.46 ꢀ 8.39 (m, 2H), 8.15 (d, J = 8.6 Hz, 1H),
7.71 ꢀ 7.67 (m, 2H), 7.63 (dd, J = 8.6, 1.8 Hz, 1H), 7.51 (s,
1H), 7.33 (d, J = 4.4 Hz, 1H), 2.49 (s, 3H); 13C NMR (100
MHz, Chloroformꢀd) δ 148.5, 147.9, 146.7, 145.7, 144.7,
137.7, 132.3, 130.5, 129.4, 126.0, 123.9, 123.7, 121.2, 21.9;
HRMS (ESI) m/z: [M + H]+ calcd for C16H13N2O2 265.0972;
Found 265.0972.
4-(4-methoxyphenyl)-6-methylquinoline (3ga).6b Purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate = 87/13) to afford 3ga as a yellow semi solid (171 mg,
4-(6-methylquinolin-4-yl)benzonitrile (3ma). Purified by colꢀ
umn chromatography on silica gel (petroleum ether/ethyl aceꢀ
tate = 85/15) to afford 3ma as a white solid (170 mg, 70%).
1
1
69%). H NMR (400 MHz, Chloroformꢀd) δ 8.85 (d, J = 4.4
mp = 163 ꢀ 165 °C. H NMR (400 MHz, Chloroformꢀd) δ =
Hz, 1H), 8.07 (d, J = 8.6 Hz, 1H), 7.71 (s, 1H), 7.56 (dd, J =
8.6, 1.9 Hz, 1H), 7.48 ꢀ 7.43 (m, 2H), 7.27 (t, J = 3.2 Hz, 1H),
7.10 ꢀ7.04 (m, 2H), 3.91 (s, 3H), 2.48 (s, 3H); 13C NMR (100
MHz, Chloroformꢀd) δ 159.8, 149.0, 147.7, 147.2, 136.5,
131.6, 130.8, 130.5, 129.4, 127.0, 124.7, 121.4, 114.1, 55.4,
21.9.
8.91 (d, J = 4.4 Hz, 1H), 8.12 (d, J = 8.6 Hz, 1H), 7.89 ꢀ 7.82
(m, 2H), 7.65 ꢀ 7.59 (m, 3H), 7.51 (s, 1H), 7.29 (d, J = 4.4 Hz,
1H), 2.49 (s, 3H); 13C NMR (100 MHz, Chloroformꢀd) δ
148.6, 146.8, 145.9, 142.8, 137.5, 132.4, 132.2, 130.2, 129.5,
125.9, 123.7, 121.1, 118.4, 112.4, 21.8; HRMS (ESI) m/z: [M
+ H]+ calcd for C17H13N2 245.1065; Found 245.1073.
4-(4-fluorophenyl)-6-methylquinoline (3ha).6b Purified by colꢀ
umn chromatography on silica gel (petroleum ether/ethyl aceꢀ
tate = 85/15) to afford 3ha as a yellow solid (156 mg, 66%).
6-methyl-4-(3-(trifluoromethyl)phenyl)quinoline (3na). Puriꢀ
fied by column chromatography on silica gel (petroleum
ether/ethyl acetate = 85/15) to afford 3na as a white solid (192
mg, 67%). mp = 69 ꢀ 71 °C. 1H NMR (400 MHz, Chloroformꢀ
d) δ 8.90 (d, J = 4.4 Hz, 1H), 8.10 (d, J = 8.6 Hz, 1H), 7.77
(dd, J = 5.2, 0.7 Hz, 2H), 7.72 ꢀ 7.64 (m, 2H), 7.58 (dd, J =
8.6, 1.9 Hz, 1H), 7.54 (s, 1H), 7.29 (d, J = 4.4 Hz, 1H), 2.47
(s, 3H); 13C NMR (100 MHz, Chloroformꢀd) δ 148.9, 147.2,
146.0, 139.0, 137.1, 132.8, 131.8, 131.2 (q, J = 32.5 Hz),
129.7, 129.0, 126.2 (q, J = 3.5 Hz), 125.3, 125.1 (q, J = 3.4
Hz), 123.9, 123.5 (q, J = 272.5 Hz), 121.4, 21.8; HRMS (ESI)
m/z: [M + H]+ calcd for C17H13NF3 288.0995; Found
288.0982.
1
mp = 90 ꢀ 92 °C. H NMR (400 MHz, Chloroformꢀd) δ 8.87
(d, J = 4.4 Hz, 1H), 8.10 (d, J = 8.6 Hz, 1H), 7.61 (s, 1H), 7.58
(dd, J = 8.6, 1.8 Hz, 1H), 7.51 ꢀ 7.44 (m, 2H), 7.28 (d, J = 4.4
Hz, 1H), 7.27 ꢀ 7.20 (m, 2H), 2.48 (s, 3H); 13C NMR (100
MHz, Chloroformꢀd) δ 162.9 (d, J = 248.1 Hz), 148.7, 147.0
(d, J = 9.2 Hz), 136.9, 134.0, 131.8, 131.2 (d, J = 8.1 Hz),
129.4, 126.7, 124.3, 121.4, 115.8, 115.6, 21.8.
4-(4-chlorophenyl)-6-methylquinoline (3ia)6b Purified by colꢀ
umn chromatography on silica gel (petroleum ether/ethyl aceꢀ
tate = 85/15) to afford 3ia as a yellow solid (184 mg, 73%).
mp = 121 ꢀ 123 °C. 1H NMR (400 MHz, Chloroformꢀd) δ 8.87
(d, J = 4.4 Hz, 1H), 8.07 (d, J = 8.5 Hz, 1H), 7.61 ꢀ 7.54 (m,
2H), 7.54 ꢀ 7.50 (m, 2H), 7.46 ꢀ 7.42 (m, 2H), 7.27 ꢀ 7.26 (m,
1H), 2.48 (s, 3H); 13C NMR (100 MHz, Chloroformꢀd) δ
149.1, 147.3, 146.5, 136.9, 136.7, 134.6, 131.8, 130.8, 129.7,
128.9, 126.5, 124.2, 121.3, 21.9.
6-methyl-4-(phenanthren-9-yl)quinoline (3oa). Purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate = 86/14) to afford 3oa as a yellow semi solid (216 mg,
68%). 1H NMR (500 MHz, Chloroformꢀd) δ 9.02 (s, 1H), 8.84
(d, J = 8.3 Hz, 1H), 8.81 (d, J = 8.3 Hz, 1H), 8.37 (d, J = 8.3
Hz, 1H), 7.94 (d, J = 8.3 Hz, 1H), 7.80 ꢀ 7.76 (m, 1H), 7.75 (s,
1H), 7.73 ꢀ 7.64 (m, 3H), 7.59 (s, 1H), 7.47 ꢀ 7.43 (m, 1H),
7.34 (d, J = 8.6 Hz, 2H), 2.33 (s, 3H); 13C NMR (100 MHz,
Chloroformꢀd) δ 149.9, 146.7, 144.0, 138.1, 133.7, 133.4,
131.0, 130.6, 130.5, 130.4, 128.9, 128.3, 127.6, 127.3, 127.1,
127.1, 126.6, 125.3, 123.1, 122.7, 21.7; HRMS (ESI) m/z: [M
+ H]+ calcd for C24H18N 320.1423; Found 320.1434.
4-(4-bromophenyl)-6-methylquinoline (3ja).6b Purified by colꢀ
umn chromatography on silica gel (petroleum ether/ethyl aceꢀ
tate = 84/16) to afford 3ja as a yellow solid (202 mg, 68%).
1
mp = 123 ꢀ 126 °C. H NMR (500 MHz, Chloroformꢀd) δ
8.88 (d, J = 4.2 Hz, 1H), 8.14 (d, J = 8.4 Hz, 1H), 7.71 ꢀ 7.66
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6-methyl-4-(pyren-1-yl)quinoline (3pa). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
7.23 (m , 2H), 3.79 (s, 3H), 2.47 (s, 3H); 13C NMR (100 MHz,
Chloroformꢀd) δ 157.8, 147.5, 147.2, 144.4, 138.3, 135.3,
130.9, 129.4, 129.2, 127.8, 121.9, 121.6, 103.7, 77.3, 77.0,
76.7, 55.4, 21.3; HRMS (ESI) m/z: [M + H]+ calcd for
C17H16NO 250.1215; Found 250.1226.
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5
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7
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86/14) to afford 3pa as a yellow solid (243 mg, 71%). mp =
1
182 ꢀ 185 °C. H NMR (500 MHz, Chloroformꢀd) δ 9.05 (s,
1H), 8.47 (d, J = 8.3 Hz, 1H), 8.33 (d, J = 7.7 Hz, 1H), 8.29
(d, J = 7.6 Hz, 1H), 8.24 ꢀ 8.17 (m, 3H), 8.07 (t, J = 7.6 Hz,
1H), 7.97 (t, J = 7.7 Hz, 2H), 7.70 (d, J = 9.7 Hz, 2H), 7.56 (d,
J = 9.1 Hz, 1H), 7.28 (s, 1H), 2.31 (s, 3H); 13C NMR (100
MHz, Chloroformꢀd) δ 151.4, 145.6, 143.1, 138.6, 133.9,
131.8, 131.5, 131.3, 130.7, 129.1, 128.6, 128.5, 127.2, 126.5,
125.9, 125.7, 125.5, 124.7, 124.6, 124.5, 124.3, 123.1, 21.7;
HRMS (ESI) m/z: [M + H]+ calcd for C24H18N 344.1426;
Found 344.1434.
6-chloro-4-(p-tolyl)quinoline (3be). Purified by column chroꢀ
matography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3be as a yellow solid (177 mg, 70%). mp =
157 ꢀ 160 °C.; 1H NMR (400 MHz, Chloroformꢀd) δ = 9.28 (s,
1H), 8.45 (d, J = 1.9 Hz, 1H), 8.14 (d, J = 9.0 Hz, 1H), 7.90
(d, J = 2.2 Hz, 1H), 7.78 (dd, J = 8.9, 2.6 Hz, 3H), 7.35 (d, J =
8.0 Hz, 2H), 2.48 (s, 3H); 13C NMR (100 MHz, Chloroformꢀd)
δ 194.1, 150.5, 147.7, 144.3, 137.4, 134.1, 133.4, 132.5, 131.1,
130.3, 129.5, 129.4, 127.5, 21.7; HRMS (ESI) m/z: [M + H]+
calcd for C16H13NCl 254.0731; Found 254.0732.
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7-methyl-4-(thiophen-3-yl)quinoline (3qa). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3qa as a yellow semi solid (140 mg, 62%). 1H
NMR (500 MHz, Chloroformꢀd) δ 9.27 (d, J = 4.5 Hz, 1H),
8.57 (d, J = 3.5 Hz, 1H), 8.10 – 8.06 (m, 1H), 7.80 (d, J = 5.1
Hz, 1H), 7.71 (d, J = 0.5 Hz, 3H), 7.24 – 7.19 (m, 1H), 2.57 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 186.3, 148.7, 148.0,
143.3, 137.8, 137.1, 135.0, 134.9, 134.1, 130.7, 129.0, 128.3,
127.8, 126.7, 21.6; HRMS (ESI) m/z: [M + H]+ calcd for
C14H12NS 226.0685; Found 226.0697.
4-(p-tolyl)-7,8-dihydro-6H-cyclopenta[g]quinoline (3bf). Puriꢀ
fied by column chromatography on silica gel (petroleum
ether/ethyl acetate = 78/22) to afford 3bf as a brown solid (192
mg, 74%). mp = 70 ꢀ 72 °C.; 1H NMR (400 MHz, Chloroformꢀ
d) δ 8.80 (d, J = 4.4 Hz, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.63 (d,
J = 8.5 Hz, 1H), 7.26 ꢀ 7.22 (m, 2H), 7.21 ꢀ 7.17 (m, 3H), 2.98
(t, J = 7.5 Hz, 2H), 2.46 (s, 3H), 2.39 (t, J = 7.4 Hz, 2H), 1.95
ꢀ 1.86 (m, 2H); 13C NMR (100 MHz, Chloroformꢀd) δ 148.5,
148.2, 147.7, 143.5, 139.7, 138.2, 137.7, 129.2, 128.9, 128.5,
128.4, 126.8, 124.8, 122.7, 35.2, 33.2, 25.6, 21.3; HRMS
(ESI) m/z: [M + H]+ calcd for C19H18N 260.1424; Found
260.1434.
7-methyl-4-(pyridin-2-yl)quinoline (3ra). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
84/16) to afford 3ra as a yellow sticky solid (132 mg, 61%).
1H NMR (400 MHz, Chloroformꢀd) δ 9.47 (d, J = 2.2 Hz,
1H), 8.77 (d, J = 4.7 Hz, 1H), 8.67 (s, 1H), 8.04 (d, J = 8.6 Hz,
1H), 7.93 – 7.79 (m, 2H), 7.68 (s, 1H), 7.57 (d, J = 8.6 Hz,
1H), 7.33 – 7.29 (m, 1H), 2.56 (s, 3H); 13C NMR (101 MHz,
Chloroformꢀd) δ 155.0, 150.1, 148.3, 146.8, 137.0, 136.9,
133.2, 132.3, 131.8, 128.8, 127.9, 127.2, 122.7, 120.8, 21.6;
HRMS (ESI) m/z: [M + H]+ calcd for C15H13N2 221.1073;
Found 221.1079.
5-methoxy-1-(p-tolyl)benzofuro[2,3-f]quinoline (3bg). Purified
by column chromatography on silica gel (petroleum
ether/ethyl acetate = 75/25) to afford 3bg as a yellow solid
1
(233 mg, 69%). mp = 120 ꢀ 122 °C. H NMR (500 MHz,
Chloroformꢀd) δ 8.99 (d, J = 4.4 Hz, 1H), 8.00 ꢀ7.92 (m, 1H),
7.59 (s, 1H), 7.48 ꢀ7.44 (m, 3H), 7.39 ꢀ 7.30 (m, 5H), 4.25 (s,
3H), 2.53 (s, 3H); 13C NMR (100 MHz, Chloroformꢀd) δ
155.9, 152.4, 148.1, 146.0, 145.1, 140.7, 138.1, 136.7, 129.3,
128.4, 126.3, 124.3, 124.0, 122.7, 119.9, 116.4, 111.9, 99.4,
56.5, 21.4; HRMS (ESI) m/z: [M + H]+ calcd for C23H18O2N
340.1325; Found 340.1332.
8-methyl-4-(p-tolyl)quinoline (3bb). Purified by column chroꢀ
matography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3bb as a yellow semi solid (180 mg, 77%). 1H
NMR (500 MHz, Chloroformꢀd) δ 8.97 (d, J = 4.4 Hz, 1H),
7.79 (d, J = 8.3 Hz, 1H), 7.58 (d, J = 6.9 Hz, 1H), 7.40 ꢀ 737
(m, 3H), 7.34 ꢀ 7.32 (m, 3H), 2.88 (s, 3H), 2.46 (s, 3H); 13C
NMR (100 MHz, Chloroformꢀd) δ 149.2, 148.4, 147.3, 138.3,
137.0, 135.4, 129.7, 129.5, 129.2, 126.9, 126.2, 124.0, 121.1,
21.3, 18.7; HRMS (ESI) m/z: [M + H]+ calcd for C17H16N
234.1277; Found 234.1274.
Preparation of 4-(4-chlorophenyl)-6-methylquinoline 1-
oxide (7):11a A solution of quinoline (3ia, 2.0 mmol) in CHCl3
(20 mL) was stirred at 0 °C for 15 min. Then mꢀCPBA (3ꢀ
chloroperbenzoic acid, 3.0 mmol) was added to the solution
and the reaction mixture was stirred at room temperature for 6
h. The reaction was quenched with saturated aqueous NaHCO3
solution (30 mL), the aqueous layer was extracted with CHCl3
(40 mL × 3). Then it was dried by Na2SO4 and concentrated
under reduced pressure. The crude product was purified by
SiO2 column chromatography (eluent: 1:9; MeOH:EtOAc) to
afford desired product Nꢀoxide (7) in 90% yield.
1H NMR (400 MHz, Chloroformꢀd) δ 8.77 – 8.72 (m, 1H),
8.52 (d, J = 6.2 Hz, 1H), 7.65 – 7.60 (m, 2H), 7.55 ꢀ 7.51 (m,
2H), 7.44 – 7.40 (m, 2H), 7.19 (d, J = 6.2 Hz, 1H), 2.49 (s,
3H); 13C NMR (100 MHz, Chloroformꢀd) δ 140.1, 139.3,
137.0, 135.6, 134.8, 134.3, 132.6, 130.8, 129.1, 128.7, 125.1,
121.4, 120.0, 21.70; HRMS (ESI) m/z: [M + H]+ calcd for
C16H13ClNO 270.0680; Found 270.0673.
5,7-dimethyl-4-(p-tolyl)quinoline (3bc). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
85/15) to afford 3bc as a brown solid (177 mg, 72%). mp =
104 ꢀ 106 °C. 1H NMR (400 MHz, Chloroformꢀd) δ = 8.70 (d,
J = 4.3 Hz, 1H), 7.76 (s, 1H), 7.18 ꢀ 7.09 (m, 4H), 7.05 ꢀ 7.03
(m, 2H), 2.42 (s, 3H), 2.36 (s, 3H), 1.92 (s, 3H); 13C NMR
(100 MHz, Chloroformꢀd) δ 149.7, 149.2, 148.2, 139.4, 139.1,
137.5, 135.3, 132.2, 128.5, 127.3, 124.5, 122.8, 77.3, 77.0,
76.7, 24.3, 21.4, 21.2; HRMS (ESI) m/z: [M + H]+ calcd for
C18H18N 248.1423; Found 248.1431.
8-methoxy-4-(p-tolyl)quinoline (3bd). Purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
82/18) to afford 3bd as a white solid (179 mg, 72%). mp = 77
4-(4-ethylphenyl)-6-methyl-2-morpholinoquinoline 1-oxide
(6):11a To a mixture of quinoline Nꢀoxide (4, 0.1 mmol), Nꢀ
morpholine 5 (0.3 mmol, 3.0 equiv) in benzene (1.0 mL) was
1
ꢀ 79 °C. H NMR (500 MHz, Chloroformꢀd) δ = 8.78 (d, J =
4.4 Hz, 1H), 8.09 (d, J = 9.2 Hz, 1H), 7.44 ꢀ 7.40 (m, 2H),
7.38 (dd, J = 9.2, 2.8 Hz, 1H), 7.34 (d, J = 7.8 Hz, 2H), 7.28 ꢀ
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The Journal of Organic Chemistry
added Cu(OAc)2 (0.01 mmol, 5.0 mol%), Ag2CO3 (0.2 mmol,
1
2
3
4
5
6
7
8
2.0 equiv) at room temperature. The reaction mixture was then
allowed to stir at 120 °C for 24 h under air atmosphere. The
reaction was cooled down to room temperature and the mixꢀ
ture was passed through a short pad of celite, washing with a
mixture of AcOEt/MeOH in a 1:1 ratio repeatedly. The organꢀ
ic layer was concentrated under reduced pressure to give a
crude oil, which was purified by column chromatography (elꢀ
uent: 40:60; MeOH:EtOAc) on silica gel to afford the desired
products 6 in 92% yield.
1H NMR (400 MHz, Chloroformꢀd) δ 8.67 – 8.63 (d, J = 9.6
Hz, 1H), 7.59 – 7.56 (m, 2H), 7.43 – 7.35 (m, 4H), 6.93 (s,
1H), 4.02 – 3.95 (m, 4H), 3.65 – 3.59 (m, 4H), 2.78 (q, J = 7.6
Hz, 2H), 2.44 (s, 3H), 1.34 (t, J = 7.6 Hz, 4H); 13C NMR (125
MHz, CDCl3) δ 149.3, 144.9, 140.7, 139.8, 136.1, 134.9,
132.8, 129.5, 128.3, 125.5, 124.5, 118.9, 113.6, 66.7, 48.1,
28.7, 21.4, 15.5; HRMS (ESI) m/z: [M + H]+ calcd for
C22H25N2O2 349.1911; Found 349.1911.
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The Department of Science and Technology (DST), India is
acknowledged for the award of DSTꢀINSPIRE Faculty award to
D.K.T. The Science and Engineering Research Board (SERB),
New Delhi India, is thanked for the financial support. M.P. is
thankful to the University Grants Commission (UGC) India for
his fellowship. S.B.W is thankful to Council of Scientific and
Industrial Research (CSIR), India for fellowship. M.P., S.B.W.
and D. K. T. gratefully acknowledge the Academy of Scientific
and Innovative Research (AcSIR) for PhD registration. The auꢀ
thors are grateful to the Director, CSIRꢀIICT, for providing the
necessary infrastructure.
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pressure the residue was purified by column chromatography
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website.
Characterization of new compounds (1H and 13C NMR spectra)
(PDF)
AUTHOR INFORMATION
Corresponding Author
*dkt80.org@gmail.com & dktiwari.iict@gov.in
Notes
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