Iron-Catalyzed Cyclization of Nitrones with Geminal-Substituted Vinyl Acetates: A Direct [4 + 2] Assembly Strategy Leading to 2,4-Disubstituted Quinolines

Article abstract of DOI:10.1021/acs.joc.6b01910

An iron-catalyzed intermolecular [4 + 2] cyclization of arylnitrones with geminal-substituted vinyl acetates was developed for the synthesis of 2,4-disubstituted quinolines in moderate to good yields with good functional group compatibilities. Preliminary mechanistic studies suggest a plausible iron-catalyzed C-H activation process under external-oxidant-free conditions.

Full text of DOI:10.1021/acs.joc.6b01910

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Article
Iron-Catalyzed Cyclization of Nitrones with Geminal-
Substituted Vinyl Acetates: A Direct [4+2] Assembly
Strategy Leading to 2,4-Disubstituted Quinolines
MingBing Zhong, Song Sun, Jiang Cheng, and Ying Shao
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01910 • Publication Date (Web): 21 Oct 2016
Downloaded from http://pubs.acs.org on October 21, 2016
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The Journal of Organic Chemistry
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Iron-Catalyzed Cyclization of Nitrones with Geminal-Substituted
Vinyl Acetates: A Direct [4+2] Assembly Strategy Leading to 2,4-
Disubstituted Quinolines
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Mingbing Zhong, Song Sun, Jiang Cheng * and Ying Shao*
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School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, Adꢀ
vanced catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University, Changzhou
213164, P. R. China.
yingshao@cczu.edu.cn
jiangcheng@cczu.edu.cn
R2
R2
O
N
N
R1
O
Fe(acac)3
+
R1
R3
O
R4
R3
ABSTRACT: An iron-catalyzed intermolecular [4+2] cyclization of arylnitrones with geminal-substituted vinyl ace-
tates was developed for the synthesis of 2,4-disubstituted quinolines in moderate to good yields with good functional
group compatibilities. Preliminary mechanistic studies suggest a plausible iron-catalyzed C-H activation process under
external-oxidant-free conditions.
Scheme 1. Medicinal Quinoline Derivatives.
■ INTRODUCTION
Quinoline derivatives exhibit pharmacologically privileged and synthetically important effects in medicinal chemis-
try, especially for the treatment of malaria (Scheme 1).1 However, most natural quinolines metabolize too fast in human
bodies, which restricts their clinical applications. Quinoline analogues, especially 2-substituted quinolines, have better
pharmacological activities due to their higher inoxidizability.2 Thus, it is meaningful to design or reform special struc-
tures of quinoline derivatives to obtain new, effective and safe medicines. While there are numerous methods for the
preparation of quinolines such as the classical Skraup quinoline synthesis, Niementowski quinoline synthesis and other
methods starting with anilines or substituted anilines,3 these reactions suffer from a variety of disadvantages viz. 1)
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external oxidants for the aromatization, 2) harsh reaction conditions, 3) noble and/or toxic metal catalysts or other addi-
tives.4 Recently, versatile methods for rapid access to 2,3-disubstituted quinolines and quinoline-4-carboxylic acid de-
rivatives starting from arylimines were reported,5 in which, palladium and indium catalysts were indispensable. In addi-
tion, production of extra wastes did not conform to the principles of green synthetic chemistry. Hence, development of
a mild, efficient and ecologically benign procedure to access such frameworks is highly desirable for organic chemists.
Due to the nature of their easy preparation and fascinating polar nature of the N-O bond, nitrones are rising to the
spotlight in heterocyclic chemistry for developing transition-metal-catalyzed C-H bond functionalization reactions.6a
Scientists obtained a variety of useful structures such as indoles and O-containing heterocycles through cascade reac-
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tions of nitrones with alkynes 6
. Unfortunately, palladium, rhodium, cobalt and other transition metals, which are ex-
pensive and/or toxic, always had to be used to activate the C-H bond of nitrones.7 Iron with multiple valence states or
its complexes, is an ideal, cheap and harmless catalyst for C-H activation in the literatures.8 Meanwhile, considering
the emergence of geminal-substituted vinyl acetates as convenient acetylene equivalents, 9 and the special oxidizing N-
O bond in nitrones which could serve as intramolecular oxidant,7c we envisioned an iron-catalyzed quinoline synthesis
could be possible using nitrones and vinyl acetates. Herein, we present a new method for the preparation of 2,4-
disubstituted quinolines from nitrones and IPA (isopropenyl acetate) derivatives catalyzed by iron, where no external
oxidant was involved because of inherent N-O bond.
■ RESULTS AND DISCUSSION
Firstly, the reaction of nitrone 1a (0.1 mmol) and IPA 2a (4.0 equiv), in the presence of FeCl2 (10 mol%), AgSbF6
(20 mol%), in MeOH (2mL) under air at 100 oC for 10 h was examined. To our surprise, the desired product 3aa was
detected in trace yield (Table 1, entry 1). Delightedly, replacing FeCl2 with Fe(NO3)3 obtained 3aa in 20% yield (Table
1, entry 2). Other iron (III) salts, such as FeBr3 and FeCl3, provided moderately improved yields (Table 1, entries3 & 4).
Gratifyingly, the yield of 3aa was increased to 78% in the presence of Fe(acac)3 (Table 1, entry 5). Furthermore, sim-
ple solvent screening revealed dichloromethane (DCM) to be most effective for this reaction (Table 1, entries 6-9).
Trace of 3aa was detected in the presence of other silver salts (Table 1, entries 10 & 11). Surprisingly, 70% yield of
3aa was obtained when NaSbF6 was used as the additive (Table 1, entry 12). Based on this result, 80% yield of 3aa
was obtained in the presence of 0.5 equiv of NaSbF6 (Table 1, entry 13). Further screening of the parameters, such as
reaction atmosphere and mole ratios between nitrones and IPA (Table 1, entries 13 & 14) established the optimized
condition as follows：nitrone 1a (0.1 mmol) and IPA 2a (4.0 equiv), in the presence of Fe(acac)3 (10 mol%), NaSbF6
(0.5 equiv), in DCM (2mL) under air at 100 oC for 10 h.
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Table 1. Screening the Reaction Conditions. a,b
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O
O
N
N
O
9
1a
2a
3aa
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Entry
Catalysts
FeCl2
Additive
AgSbF6
AgSbF6
Solvent
Yieldc (%)
< 5
1
2
MeOH
MeOH
Fe(NO3)3
20
3
4
5
6
FeBr3
FeCl3
AgSbF6
AgSbF6
AgSbF6
AgSbF6
MeOH
MeOH
MeOH
EtOH
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24
78
55
Fe(acac)3
Fe(acac)3
7
8
Fe(acac)3
Fe(acac)3
AgSbF6
AgSbF6
Acetone
Benzene
81
77
83, 79 d, 77 e
trace
9
Fe(acac)3
Fe(acac)3
Fe(acac)3
AgSbF6
AgCl
DCM
DCM
DCM
10
11
Ag2CO3
trace
12
13
14
Fe(acac)3
Fe(acac)3
Fe(acac)3
NaSbF6
DCM
DCM
DCM
70
NaSbF6
80, 81g, 75h
37i, 61j
f
f
NaSbF6
a Unless otherwise noted, the reaction was carried out on 1a (0.1 mmol), 2a (4.0 equiv), catalyst (10 mol%), additive (20 mol%) in sol-
o
b
vent (2.0 mL) at 100 C for 10 h under air atmosphere in a sealed tube. Detailed information please see Table S1, in Supporting Infor-
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c
d
o
e
o
g
h
i
mation. Isolated yield. At 90 C. At 120 C. f NaSbF6 (0.5 equiv). Under N2 atmophere. Under O2 atmophere. Mole ratio,
1a:2a=1:1. j Mole ratio, 1a:2a=1:2.
With the optimal conditions in hand, we next investigated the substrate scope of arylnitrones (Table 2). Arylnitrones
could be easily prepared from arylaldehyde and arylhydroxylamine easily according to the literatures.10 This reaction
displayed excellent functional group tolerance. Both electron-donating and withdrawing groups, such as 4-methyl (1b,
1o), 4-methoxyl (1i), 4-methylthio (1j), 4-halogens (1d-f, 1l-m), 4-trifluoromethyl (1g) and 4-cyano (1h) at the
phenylimino moieties are compatible with this reaction, providing the corresponding quinoline products in moderate to
good yields. Metaꢀsubstituted R2 group also worked efficiently, affording 3ca in 75% yield. Similar efficiencies were
also observed, when R1 groups is located at the meta- or para- positions with 3la, 3ma, 3na, 3oa and 3pa obtained in
78% to 83% yields. In addition, nitrone containing the 2-naphthyl group also worked well in this reaction (3ka) with
89% yield. However, 1-naphthyl nitrone (1k’) failed to provide any products. Furthermore, other heterocyclic nitrones
were are also not compatible with this reaction (Figure S1, 1u, 1v, 1w), most likely due to the strong metal-heteroatom
coordination interactions, which were known to interfere with Fe catalyzed ortho-CAr-H activations.11 In addition,
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ortho-substitions of either phenyl rings (Figure S1, 1q, 1r, 1s, 1t) only provided trace products, indicating this reaction
is sensitive to steric hinderance. Lastly, all attempts to access 2-alkylquinolines failed (Figure S1, 1x, 1y, 1z, 1a’).
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Table 2. Substrate Scope of Arylnitrones a,b
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R2
R2
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O
N
Fe(acac)3 (10 mol%)
NaSbF6 (0.5 equiv)
CH2Cl2, 100 oC, 10 h
N
O
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R1
O
R1
1
2a
3
N
N
N
3aa, 80%
3ba, 77%
3ca, 75%
F
Cl
Br
N
N
N
3da, 76%
3ea, 75%
3fa, 78%
CF3
CN
OMe
N
N
N
3ga, 69%
3ha, 85%
3ia, 67%
S
N
N
N
Br
3ja, 65%
3ka, 89%
3la, 78%
N
Cl
N
N
Cl
3ma, 81%
3na, 79%
3oa, 83%
R'
N
R
N
N
R''
n.d.c
n.d.c
3pa, 79%
R' = H, R" = Cl, Me or OH
or R' = MeO, R'' = H
R = 2-thienyl, 2-furyl or
3-pyridyl
a
Unless otherwise noted, the reaction was carried out on 1 (0.1 mmol), 2a (4.0 equiv), Fe(acac)3 (10 mol%), NaSbF6 (0.5 equiv) in
DCM (2.0 mL) at 100 C for 10 h under air atmosphere in a sealed tube. Isolated yield. c Detailed information please see Figure S1, in
o
b
Supporting Information.
Table 3. Substrate Scope of Vinyl Acetates a,b
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N
Ph
O
1
2
3
O
N
standard conditions
Ph
R3
O
Ph
R3
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1a
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3
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Ph
N
Ph
N
Ph
Ph
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3ab, 57%
3ad, 83%
3ac, 81%
N
N
Ph
Cl
OMe
3ae, 75%
3af, 76%
a
24
Unless otherwise noted, the reaction was carried out on 1a (0.1 mmol), 2 (4.0 equiv), Fe(acac)3 (10 mol%), NaSbF6 (0.5 equiv) in
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DCM (2.0 mL) at 100 oC for 10 h under air atmosphere in a sealed tube. b Isolated yield.
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Next, we surveyed the geminal-substituted vinyl acetate scope of this iron-catalyzed annulation (Table 3). Notably,
when R3 adopted aryl groups, these vinyl acetates could afford the corresponding quinolines (3ac-3af) in good yields
of 75% to 83%. In the absence of the aryl group, however, 3ab only gave 57% yield. This reactivity difference can be
explained probably by the stability of the carbocation generated in intermediate D in our proposed mechanism.12 Fur-
thermore, 2-thiophenyl substituted vinyl acetates 2g was also a difficult partner for this reaction (Figure S2), probably
due to the metal coordination-chelation interaction as discussed above. The reaction can be further diversified when
methyl methacrylate and tbutyl acrylate were used to replace vinyl acetate, affording the desired products 3aa and 3ab
in 51% and 75% yield, respectively (Figure 1). According to our originally envisaged mechanism, we can roughly
explain the reason that R3 group is hydrogen and the secondary carbocation is less stable in the solution (the
intermediate D in the proposed mechanism).12
Figure 1. Substrate Scope of Acrylates a,b
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a
Unless otherwise noted, the reaction was carried out on 1a (0.1 mmol), 4 (4.0 equiv), Fe(acac)3 (10 mol%), NaSbF6 (0.5 equiv) in
1
2
DCM (2.0 mL) at 100 oC for 10 h under air atmosphere in a sealed tube. b Isolated yield.
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Scheme 2. Preliminary Mechanistic Studies.
Preliminary mechanistic studies were conducted to get some insights into this transformation (Scheme 2). With the
help of a Lewis acid, the attack of nitrone by vinyl acetate followed by an intramolecular addition may be involved.
However, replacing Fe(acac)3 with other strong Lewis acids, such as Cu(OTf)2, CeCl3, BF3•OEt2 or Brønsted acid
HOTf shut down the reaction. The absence of the desired product and possible byproduct (eq 1) indicated that this re-
action was unlikely to follow a Lewis acid catalyzed pathway. Another mechanism starting with a [3+2] cycloaddition,
followed by an iron-catalyzed ring-opening reaction, where Fe(III) acted as Lewis acid was also reasonable. However,
the potential [3+2] cyclization intermediate was also not detected (eq 2). Generally speaking, this transformation may
not match the characteristics of a Lewis acid catalyzed reaction. 13 Although at the current stage, none of them can be
thoroughly ruled out, an iron-catalyzed C-H activation pathway was favored.
Iron(III)-catalyzed C-H activation has been widely developed in the past decades.8, 14 In light of foregoing experi-
ments and literatures, a plausible mechanism was proposed as shown in Scheme 3. Cleavage of the C-H bond by
iron(III) at the ortho-position of the phenyl ring via N-Oxide serving as directing group generates intermediate A. IPA
insertion to A followed by β-O elimination affords intermediate C. The iminium species C1 can be delocalized to gen-
erate a carbocation C2. Imine addition or intramolecular olefin addition into the carbocation followed by E1 elimina-
tion provides the key intermediate D. Subsequent β-H elimination generates the quinoline N-Oxide E, which might
briefly show up in the system but was undetectable. Internal oxidation cleaves the N-O bond to produce the desired
quinoline product and regenerates the iron(III) catalyst, thereby closing the catalytic cycle. Acetic acid and water were
the only byproducts.
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Scheme 3. Proposed Mechanism.
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■ CONCLUSIONS
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In conclusion, we have developed an iron-catalyzed annulation of nitrones with geminal-substituted vinyl acetates
for the synthesis of 2,4-disubstituted quinolines. This transformation features: 1) iron-catalyzed C-H activation process
based on preliminary mechanistic investigations; 2) mild conditions with inexpensive transition-metal and internal-
oxidant; 3) diverse substrates and good functional group tolerance; 4) dual functionality of N-Oxide as both a directing
group and an oxidant and 5) green chemistry with water and acetic acid as byproducts.
■ EXPERIMENTAL SECTION
General Information
Unless otherwise noted, all chemicals were purchased from commercial suppliers and used without further purifica-
tion. 1H NMR and 13C NMR spectra were recorded at ambient temperature on a 300 or 400 MHz NMR spectrometer
(75 MHz for 13C, 100 MHz for 13C). NMR experiments are reported in δ units, parts per million (ppm), and were refer-
enced to CDCl3 (7.26 or 77.0 ppm) as the internal standard. The coupling constants J are given in Hz. Column chroma-
tography was performed using Silica gel 60 (300-400 mesh). Melting points were taken on an electro thermal melting
point apparatus and without correction. IR spectra were recorded on a FT-IR spectrometer using KBr discs. HRMS
spectra were recorded using a spectrometer with a TOF mass analyzer with an ESI ion source.
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General Procedure for Preparation of quinolones
Page 8 of 15
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Under air atmosphere, a sealed tube was charged with diarylnitrones (0.1 mmol), ferric acetylacetonate (3.5 mg, 10
mol%), geminal-substituted vinyl acetates (4.0 mmol), NaSbF6 (12.9 mg, 50 mol%), DCM (2.0 mL). The reaction mix-
ture was stirred at 100 °C for 10 h in oil bath. After the completion of the reaction, 2 mL saturated sodium hydroxide
solution and 3×2 mL EtOAc were added, the combined organic phase was concentrated in vacuum and the residue
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was purified by flash column chromatography on silica gel with petroleum ether-ethyl acetate as the eluent to give the
desired product.
General procedure for the arylnitrones 10a
Nitroarene (1.0 equiv), aldehyde (1.1 equiv) and NH4Cl (1.2 equiv) were dissolved in a 1:1 mixture of EtOH and
water (2 mL/mmol of starting material) and cooled to 0°C (ice bath). Then zinc powder (2.0 equiv) was added to the
resulting mixture, and the reaction was allowed to warm to room temperature and stirred for 16 hours. The reaction
mixture was filtered and washed with CH2Cl2. The filtrate was extracted with CH2Cl2 (4×50 mL) and the combined
organic layer was washed with brine, dried over MgSO4, concentrated under reduced pressure to give crude nitrones.
Pure nitrones were obtained by recrystallization from ethyl acetate.
General procedure for the 1-phenylvinyl acetate 15
To a mixture of acetophenone (4.85 mL, 5 g, 42.5 mmol) and 2-propenyl acetate (23.13 mL, 0.213 mol, 5.0 equiv.),
p-toluenesulfonic acid (0.75 g, 3.925 mmol, 0.09 equiv) was added. The resulting mixture was refluxed for 20 h in a
100 mL flask equipped with a condenser and a drying tube. The solvent was then cooled to room temperature, and the
solvent was evaporated in vacuo. Ether was added (100 mL), and the resulting solvent was washed with water (3 × 50
mL) and dried over MgSO4. The solvent was evaporated in vacuo to give a dark orange/red oily residue. This residue
was purified by column chromatography on silica gel to yield yellow oil. Sometimes a further distillation to remove
remained acetophenone is necessary.
4-Methyl-2-phenylquinoline (3aa) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3aa (17.5 mg, 80% yield) as a
yellow solid: mp 62-63 oC; 1H NMR (CDCl3, 400 MHz) δ 8.20-8.15 (m, 3H), 8.00 (d, J = 8.2 Hz, 1H), 7.71-7.74 (m,
2H), 7.45-7.51 (m, 4H), 2.77 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 157.0, 148.1, 144.8, 139.8, 130.2, 129.3, 129.1,
128.7, 127.5, 127.2, 126.0, 123.6, 119.7, 19.0; MS (EI): 219 (M+).
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4-Methyl-2-(p-tolyl)quinoline (3ba) 13b
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give the product 3ba (18.0 mg,
77% yield) as a yellow solid: mp 76-78 oC; 1H NMR (CDCl3, 300 MHz) δ 8.18-8.15 (m, 1H), 8.07-8.04 (m, 2H), 8.01-
7.98 (m, 1H), 7.74-7.68 (m, 2H), 7.56-7.51 (m, 1H), 7.34-7.31 (m, 2H), 2.76 (d, J = 0.9 Hz, 3H), 2.43 (s, 3H); 13C
NMR (CDCl3, 75 MHz) δ 157.0, 148.0, 144.7, 139.2, 136.9, 130.1 129.5, 129.3, 127.4, 127.2, 125.8 123.6, 119.6,
21.3, 19.0; MS (EI): 233 (M+).
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4-Methyl-2-(m-tolyl)quinoline (3ca) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ca (17.4 mg, 75% yield) as a
1
yellowish solid: mp 77-78 oC; H NMR (CDCl3, 300 MHz) δ 8.17-8.14 (m, 1H), 7.99 (t, J = 4.0 Hz, 2H), 7.88 (d, J =
7.7 Hz, 1H), 7.71-7.66 (m, 2H), 7.54-7.49 (m, 1H), 7.38 (t, J = 7.6 Hz, 1H), 7.23 (s, 1H), 2.74 (d, J = 0.9 Hz, 3H), 2.45
(s, 3H); 13C NMR (CDCl3, 75 MHz) δ 157.3, 148.0, 144.7, 139.7, 138.4, 130.2, 130.0, 129.3, 128.6, 128.2, 127.2,
126.0, 124.6, 123.6, 119.9, 21.6, 19.0; MS (EI): 233 (M+).
2-(4-Fluorophenyl)-4-methylquinoline (3da) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3da (18.0 mg, 76% yield) as a
yellowish oil; 1H NMR (CDCl3, 400 MHz) δ 8.17-8.13 (m, 3H), 8.00 (d, J = 8.3 Hz, 1H), 7.74-7.67 (m, 2H), 7.57-7.53
(m, 1H), 7.20 (t, J = 8.7 Hz, 2H), 2.77 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 164.9, 162.5, 155.9, 148.0, 145.0, 135.9
(d, JCꢀF = 4.0 Hz), 130.2, 129.3 (d, JCꢀF = 16.0 Hz), 127.1, 126.1, 123.6, 119.4, 115.7 (d, JCꢀF = 22.0 Hz), 19.0; MS (EI):
237 (M+).
2-(4-Chlorophenyl)-4-methylquinoline (3ea) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ea (18.5 mg, 75% yield) as a
yellowish solid: mp 74-75 oC; 1H NMR (CDCl3, 400 MHz) δ 8.17-8.10 (m, 3H), 8.00 (d, J = 8.3 Hz, 1H), 7.75-7.68 (m,
2H), 7.58-7.48 (m, 3H), 2.77 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 155.7, 145.0, 138.2, 135.4, 130.3, 129.5, 129.3,
128.9, 128.76, 127.3, 126.2, 123.6, 119.3, 19.0; MS (EI): 253 (M+).
2-(4-Bromophenyl)-4-methylquinoline (3fa) 13b
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3fa (23.2 mg, 78% yield) as a
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yellowish solid: mp 68-69 C; H NMR (CDCl3, 400 MHz) δ 8.17-8.10 (m, 3H), 8.00 (d, J = 8.2 Hz, 1H), 7.74-7.68
(m, 2H), 7.55-7.48 (m, 3H), 2.77 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 155.7, 148.1, 145.0, 138.2, 135.2, 135.4,
130.2, 129.5, 128.9, 128.8, 127.3, 126.2, 123.6, 119.3,19.0; MS (EI): 297 (M+).
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4-Methyl-2-(4-(trifluoromethyl)phenyl)quinoline (3ga) 16
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ga (19.8 mg, 69% yield) as a
yellow solid: mp 117-118 oC; 1H NMR (CDCl3, 300 MHz) δ 8.27 (d, J = 10.7 Hz, 2H), 8.20-8.17 (m, 1H), 8.04-8.01
(m, 1H), 7.79-7.62 (m, 4H), 7.62-7.56 (m, 1H), 2.79 (d, J = 1.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 155.4, 148.0,
145.4, 137.1, 131.7 (d, JCꢀF = 52.5 Hz), 129.7, 127.8, 127.5, 126.6, 125.7 (t, JCꢀF = 4.1 Hz), 125.6, 123.7, 120.0, 19.1;
MS (EI): 287 (M+).
4-(4-Methylquinolin-2-yl)benzonitrile (3ha)
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ha (20.7 mg, 85% yield) as a
yellowish solid: mp 146-147 oC; 1H NMR (CDCl3, 300 MHz) δ 8.30-8.27 (m, 2H), 8.17 (d, J = 8.5 Hz, 1H), 8.05-8.02
(m, 1H), 7.82-7.73 (m, 4H), 7.63-7.57 (m, 1H), 2.80 (d, J = 0.8 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 155.0, 144.4,
139.1, 127.6, 133.5, 129.5, 127.9, 127.6, 127.3, 126.8, 125.1, 121.2, 119.8, 21.4, 19.4; MS (EI): 244 (M+);HRMS
(ESI) m/z calcd for C17H13N2 (M+H)+ 245.1073, found 245.1076; IR (KBr) ν 3030, 2921, 2850, 1636, 1465, 1384.
2-(4-Methoxyphenyl)-4-methylquinoline (3ia) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ia (16.7 mg, 67% yield) as a
yellowish solid: 110-112 oC; 1H NMR (CDCl3, 300 MHz) δ 8.15-8.10 (m, 3H), 8.00-7.96 (m, 1H), 7.68 (s, 1H), 7.54-
7.44 (m, 2 H), 7.07-7.02 (m, 2H), 3.89 (s, 3H), 2.75 (d, J = 0.9 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 160.7, 156.6,
148.1, 144.6, 130.0, 129.3, 129.2, 128.8, 127.7, 125.7, 123.6, 119.3, 114.1, 55.4, 19.0; MS (EI): 249 (M+).
4-Methyl-2-(4-(methylthio)phenyl)quinoline (3ja)
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ja (17.2 mg, 65% yield) as a
yellowish solid: 135-136 oC; 1H NMR (CDCl3, 400 MHz) δ 8.19-8.11 (m, 3H), 8.01 (d, J = 8.3 Hz, 1H), 7.75-7.71 (m,
2H),7.58-7.54 (m, 1H), 7.41 (d, J = 8.4 Hz, 2H), 2.79 (s, 3H), 2.57 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 156.3,
148.1, 144.8, 140.2, 136.4, 130.1, 129.4, 127.8, 126.4, 125.9, 123.6, 119.3, 112.8, 19.0, 15.5; MS (EI): 265
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(M+);HRMS (ESI) m/z calcd for C17H16NS (M+H)+ 266.0998, found 266.1002; IR (KBr) ν 3030, 2920, 2850, 1634,
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1595, 1494, 1385.
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4-Methyl-2,2'-binaphthalene (3ka) 13b
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ka (23.9mg, 89% yield) as a
yellowish solid: mp 96-97 oC; 1H NMR (CDCl3, 400 MHz) δ 8.35 (d, J = 8.4 Hz, 1H), 8.24 (d, J = 8.4 Hz, 1H), 8.05 (d,
J = 8.3 Hz, 1H), 7.98-7.95 (m, 2H), 7.81-7.76 (m, 2H), 7.64-7.50 (m, 5H), 2.73 (s, 3H); 13C NMR (CDCl3, 100 MHz)
δ 158.8, 147.6, 144.2, 138.5, 133.7, 131.0, 129.9, 129.2, 128.7, 128.1, 127.4, 126.8, 126.3, 126.0, 125.7, 125.5, 125.1,
123.6, 126.4, 18.5; MS (EI): 269 (M+).
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6-Bromo-4-methyl-2-phenylquinoline (3la) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3la (23.2 mg, 78% yield) as
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yellowish solid: 77-79 C; H NMR (CDCl3, 300 MHz) δ 8.15-8.12 (m, 3H), 8.02 (d, J = 8.9 Hz, 1H), 7.79-7.72 (m,
2H), 7.53-7.47 (m, 3H), 2.72 (d, J = 1.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 157.4, 146.7, 144.0, 139.3, 132.7,
131.9, 129.5, 128.8, 127.5, 126.1, 120.4, 120.0, 19.0; MS (EI): 297 (M+).
6-Chloro-4-methyl-2-phenylquinoline (3ma) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ma (20.4 mg, 81% yield) as a
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yellowish solid: mp 78-79 C; H NMR (CDCl3, 400 MHz) δ 8.15-8.09 (m, 3H), 7.96 (d, J = 2.2 Hz , 1H), 7.73 (s,
1H), 7.66-7.63 (m, 1H), 7.55-7.46 (m, 3H), 2.73 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 157.3, 146.5, 144.0, 139.3,
131.8, 130.2, 129.4, 129.0, 128.8, 127.4, 122.8, 120.4, 113.9, 19.0; MS (EI): 253 (M+).
7-Chloro-4-methyl-2-phenylquinoline (3na) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3na (20.1 mg, 79% yield) as a
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yellowish solid: mp 81-83 C; H NMR (CDCl3, 300 MHz) δ 8.17-8.12 (m, 3H), 7.90 (m, 1H), 7.69 (d, J = 1.1 Hz,
1H), 7.56-7.34 (m, 4H), 2.73 (d, J = 1.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 158.0, 144.9, 139.2, 135.1, 129.5,
129.0, 128.8, 128.7, 127.5, 127.4, 126.8, 125.0, 119.9, 19.0; MS (EI): 253 (M+).
4,6-Dimethyl-2-phenylquinoline (3oa) 13b
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3oa (19.3 mg, 83% yield) as a
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yellow solid: mp 81-83 C; H NMR (CDCl3, 300 MHz) δ 8.14-8.11 (m, 2H), 8.07 (d, J = 8.6 Hz, 1H), 7.72 (s, 1H),
7.62 (s, 1H), 7.57-7.43 (m, 4H), 2.72 (d, J = 0.8 Hz, 3H), 2.58 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 157.3, 148.0,
144.7, 138.4, 130.2, 130.0, 129.3, 128.6, 128.2, 126.0, 124.6, 123.6, 119.9, 21.6, 19.0; MS (EI): 233 (M+).
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4,6,7-Trimethyl-2-phenylquinoline (3pa)
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3pa (19.5 mg, 79% yield) as
yellowish solid: mp 85-87 oC; 1H NMR (CDCl3, 300 MHz) δ 8.14-8.11 (m, 2H), 8.07 (d, J = 8.6 Hz ,1H), 7.75 (s, 1H),
7.68 (s, 1H), 7.57-7.43 (m, 3H), 2.74 (d, J = 0.8 Hz, 3H), 2.58 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 156.2, 147.2,
143.8, 140.1, 139.4, 135.8, 129.6, 128.9, 128.7, 127.4, 125.7, 123.0, 119.1, 20.3, 19.0; MS (EI): 247 (M+); HRMS
(ESI) m/z calcd for C18H18N (M+H)+ 248.1434, found 248.1436; IR (KBr) ν 2922, 852, 1637, 1551, 1452.
2-Phenylquinoline (3ab) 13b
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ab (15.3 mg, 75% yield) as a
yellowish oil; 1H NMR (CDCl3, 300 MHz) δ 8.25-8.14 (m, 4H), 7.89 (d, J = 8.6 Hz, 1H), 7.85-7.82 (m, 1H), 7.76-7.71
(m, 1H), 7.57-7.44 (m, 4H); 13C NMR (CDCl3, 75 MHz) δ 157.4, 148.3, 139.7, 136.8, 129.7, 129.6, 129.3, 128.8,
127.6, 127.4, 127.2, 126.3, 119.0; MS (EI): 205 (M+).
2,4-Diphenylquinoline (3ac) 17
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ac (22.7 mg, 81% yield) as a
yellow oil; 1H NMR (CDCl3, 300 MHz) δ 8.28 (d, J = 8.4 Hz, 1H), 8.09-8.07 (m, 2H), 7.80-7.76 (m, 1H), 7.68 (s, 1H),
7.64-7.58 (m, 1H), 7.42-7.32 (m, 9H); 13C NMR (CDCl3, 75 MHz) δ 156.8, 149.1, 148.8, 139.6, 138.3, 130.1, 129.5,
129.5, 129.3, 128.8, 128.5, 128.4, 127.5, 126.3, 125.7, 125.6, 119.3; MS (EI): 281 (M+).
2-Phenyl-4-(p-tolyl)quinoline (3ad) 17
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ad (24.5 mg, 83% yield) as a
yellow oil; 1H NMR (CDCl3, 300 MHz) δ 8.13-8.04 (m, 3H), 7.79 (d, J = 8.4 Hz, 1H), 7.66 (s, 1H), 7.57 (t, J = 7.6 Hz,
1H), 7.40-7.28 (m, 6H), 7.20 (m, 2H), 2.32 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 156.8, 149.1, 148.7, 139.6, 138.2,
135.3, 130.0, 129.4, 129.2, 128.7, 127.5, 126.1, 125.8, 125.6, 119.2, 21.2; MS (EI): 295 (M+).
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4-(4-Chlorophenyl)-2-phenylquinoline (3ae) 17
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3ae (23.6 mg, 75% yield) as a
yellow oil; 1H NMR (CDCl3, 300 MHz) δ 8.28-8.25 (m, 1H), 8.21-8.17 (m, 2H), 7.87-7.83 (m, 1H), 7.79-7.70 (m, 2H),
7.57-7.44 (m, 8H); 13C NMR (CDCl3, 75 MHz) δ 156.8, 148.7, 147.8, 193.4, 136.7, 134.6, 130.8, 130.2, 129.6, 129.4,
128.8, 128.7, 127.5, 126.5, 125.4, 125.2, 119.2; MS (EI): 315 (M+).
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4-(4-Methoxyphenyl)-2-phenylquinoline (3af) 17
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 10) give 3af (23.7 mg, 76% yield) as a
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yellow oil; H NMR (CDCl3, 300 MHz) δ 8.16-8.13, (m, 1H), 8.09-8.05 (m, 2H), 7.85-7.81 (m, 1H), 7.67 (s, 1H),
7.63-7.57 (m, 1H), 7.43-7.31 (m, 6H), 6.97-6.92 (m, 2H), 3.76 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 159.8, 156.9,
148.8, 139.7, 130.8, 130.6, 130.1, 129.4, 129.3, 128.8, 127.5, 126.2, 125.9, 125.6, 119.3, 114.0, 55.4 ; MS (EI): 311
(M+).
■ ASSOCIATED CONTENT
Experimental details on the reaction condition studies, along with copies of H, 13C NMR spectra of compounds 3aa-
1
3pa, 3ab-3af. This material is available free of charge via the Internet at http://pubs.acs.org.
■ ACKNOWLEDGMENTS
A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD),
NSFC (21302015), the Jiangsu Planned Projects for Postdoctoral Research Fund (No. 1501094B), and the China Post-
doctoral Science Foundation funded project.
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