2-Carbomethoxy-3-hydroxyquinoxaline-di-N-oxide as a novel ligand for the copper-catalyzed coupling reaction of phenols and aryl halides

Article abstract of DOI:10.1039/c2ob26556g

2-Carbomethoxy-3-hydroxyquinoxaline-di-N-oxide was identified as an efficient novel ligand for the copper-catalyzed coupling of aryl halides with various phenols under mild conditions. The catalytic system shows great functional-group tolerance and excellent reactive selectivity.

Full text of DOI:10.1039/c2ob26556g

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2-Carbomethoxy-3-hydroxyquinoxaline-di-N-oxide as a
novel ligand for the copper-catalyzed coupling reaction
of phenols and aryl halides†
Cite this: Org. Biomol. Chem., 2013, 11,
1502
Yatao Qiu,‡a,b Weijun Jia,‡a Zhiyi Yao,a Fanhong Wua and Sheng Jiang*b
Received 9th May 2012,
Accepted 21st December 2012
2-Carbomethoxy-3-hydroxyquinoxaline-di-N-oxide was identified as an efficient novel ligand for the
copper-catalyzed coupling of aryl halides with various phenols under mild conditions. The catalytic
system shows great functional-group tolerance and excellent reactive selectivity.
DOI: 10.1039/c2ob26556g
www.rsc.org/obc
2-carbomethoxy-3-hydroxyquinoxaline-di-N-oxide as an efficient
novel ligand for the formation of diaryl ethers.
Introduction
The diaryl ether motif is commonly found in many natural
products, polymers, and pharmaceutically active com-
pounds.1,2 Because the classic Ullmann ether synthesis is
carried out under relatively harsh conditions, such as high
temperatures (125–220 °C) and stoichiometric amounts of the
catalyst, namely copper (Cu), with only low to moderate yields,
much effort has been devoted to finding direct and efficient
processes for preparation of biaryl ethers.3 Using transition-
metal catalysts, such as palladium (Pd), copper (Cu), and iron
(Fe), has achieved extraordinary improvement in the formation
of the C–O bond.4–6 Because Pd catalysts are expensive, the
application of Pd-catalyzed methods has thus far been limited
to small-scale production. Cu-catalyzed Ullmann coupling
between an aryl halide and phenol/alcohols is a viable alterna-
tive to Pd-catalyzed diaryl ether synthesis. Recently, a major
progress has been made in modifying the Cu-catalyzed
Ullmann coupling reaction by using several special ligands,
such as 1-naphthoic acid, 1,10-phenanthroline, neocuproine,
triphenylphosphine, 2,6,6-tetramethylheptane-3,5-dione, tetra-
ethyl orthosilicate, N,N-dimethylglycine, diimine ligands,
β-keto esters, tripod ligands and bipyridyl complexes.3
However, only a few ligands were reported for the copper cata-
lyzed coupling of aryl chlorides with phenols.5j,o,s It is essential
to search for other new, less costly, and versatile ligands that
can be used in this Cu-catalyzed protocol. Herein, we report
Results and discussion
By analyzing the structural features of previously reported
ligands of the Cu-catalyzed Ullman reaction, we found that
most of them contained bidentate chelating centers consisting
of coordinating atoms such as oxygen and/or nitrogen atoms,
which might coordinate with a Cu ion to form a transitional
5- or 6-membered ring. The ligands that coordinate with the
metal center constitute the most important factor in deter-
mining the efficiency of the catalytic system. Based on this
survey, 2-carbomethoxy-3-hydroxyquinoxaline-di-N-oxide (L1),
in which the oxygen atom of nitrogen oxide (1), the oxygen
atom of the carbomethoxy group (2), another oxygen atom (3),
and the oxygen atom of the second nitrogen oxide (4; Fig. 1)
might form transitional 6-membered and 5-membered rings
with the Cu ion, was designed as a novel potential tetradentate
ligand to improve Cu-catalyzed cross-couplings.
To evaluate the catalytic activity of the thus-designed
ligand, we first chose iodobenzene as the model substrate to
react with phenol, and the results are summarized in Table 1.
Clearly, 2-carbomethoxy-3-hydroxyquinoxaline-di-N-oxide (L1)
can successfully promote the Cu-catalyzed coupling reac-
tion and produce high yield (90%). Interestingly, due to the
aCollege of Chemical and Environmental Engineering, Shanghai Institute of
Technology, Shanghai 210032, China
bLaboratory of Medicinal Chemistry, Guangzhou Institute of Biomedicine and
Health, CAS, Guangzhou, Guangdong 510530, P.R. China.
E-mail: jiang_sheng@gibh.ac.cn; Fax: +86-20-32290439
†Electronic supplementary information (ESI) available: 1H NMR and 13C NMR
spectra of all compounds. See DOI: 10.1039/c2ob26556g
‡These authors contributed equally to the work.
Fig. 1 Structure of the ligands designed in this study.
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electron-donating (5e) groups. However, the sterically hindered
phenols are slightly disfavored in this reaction. For example,
when 2,4-di-tert-butylphenol was used as the substrate, the
reaction gave considerably lower yield in comparison with that
of less-hindered phenols (compare 5f, 5g, and 5h). Addition-
ally, the relatively lower yield for phenol in comparison with
the electron-donating group of phenol implies that the elec-
tron-donating group of phenol is favored for the coupling reac-
tion (compare 5i and 5j). The poor yield for the reaction of
phenyl bromide with phenol resulted from low conversion
(5a). We also tested the coupling reaction of alkyl alcohols
such as ethanol, n-butanol and isopropanol with aryl bro-
mides. However the yield is very low.
Table 1 Copper-catalyzed O-arylation of phenol with iodobenzene: optimiz-
ation of the reaction conditionsa
Entry
[Cu]
Ligand
Base
Yieldb (%)
1
2
3
4
5
CuI
CuI
CuBr
CuI
CuI
L1
L2
L1
L1
L1
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K3PO4
90
33
82
39
5
Due to their low cost and ready availability, aryl chlorides
are attractive substrates for both industrial production and lab-
oratory preparation of diaryl ethers. Therefore, we further
investigated the potential catalytic efficiency of the present cat-
alytic system for the coupling reaction of aryl chlorides and
phenols. As shown in Table 4, electron-deficient (7a–7i) aryl
chlorides are suitable substrates for this reaction, and they
produce the corresponding diaryl ethers in good to excellent
yields. In the aryl iodide component, the substituent position
of the nitro group slightly influences the yield of the coupling
reaction (7a versus 7b, and 7d–7f versus 7g–7i). For example,
when 1-chloro-4-nitrobenzene reacted with phenol, the yield
was 84%. The yield improved to 97% when 1-chloro-2-nitro-
benzene reacted with phenol (7a and 7b). It is noteworthy that
the reaction of 1-chloro-2-nitrobenzene or 1-chloro-4-nitroben-
zene with sterically hindered phenols, such as 2,4-di-tert-butyl-
phenol, which are difficult cases for the classical Ullmann
coupling method, gave the product of the coupling reaction at
89% and 91% yields, respectively (7e and 7i). Additionally,
high yields were also obtained for other substrates, such as
2-naphthol, 8-hydroxyquinoline and N-(4-hydroxyphenyl)aceta-
mide, when aryl chlorides with electron-withdrawing groups
were used (7c, 7d, and 7f–7i). In addition, very lower yields
were obtained after 20 h when 1-chloro-2-nitrobenzene was
reacted with phenol at 110 °C when the copper catalyst or the
ligand was absent.
As described in Fig. 2, we have formulated a possible mech-
anism for the copper-catalyzed coupling of aryl halides with
various phenols, which is based on the previously proposed
mechanism.1–3 The chelating CuI with 2-carbomethoxy-3-
hydroxyquinoxaline-di-N-oxide (L1) formed a six-membered
and five-membered reactive species 8, and the subsequent oxi-
dative addition of the chelating species with aryl halides led to
the intermediate 9. In the presence of a base, various phenols
reacted with intermediate 8 readily to afford intermediate 11,
followed by reductive elimination to provide the desired
product and regenerate active Cu(I) species 8.
a Reaction conditions: [Cu] (0.01 mmol), ligand (0.02 mmol),
iodobenzene (0.1 mmol), phenol (0.11 mmol), Cs2CO3 (0.25 mmol),
100 °C. b Isolated yield.
absence of an oxygen atom, L2 (1,1,1-trifluoro-3-(pyridin-2-yl)-
propan-2-one) showed much lower efficiency (entries 1 and 2).
After evaluation of the catalytic efficiency of L1 and L2, the
conditions for catalysis, including the source of Cu and the
base, were also optimized. The experimental results showed
that CuI was more efficient than CuBr (entries 1 and 3),
whereas cesium carbonate (Cs2CO3) was the best among the
various bases tested (entries 1, 4, and 5). Thus, the optimized
reaction conditions were as follows: 10 mol% of Cu(I), 20 mol
% of L1, and 2.5 equiv. of Cs2CO3 in 0.5 M DMF (as a solvent)
reacting at a temperature of 100 °C under a nitrogen
atmosphere.
To define the scope of the CuI-catalyzed O-arylation reac-
tion, we applied this process to several different aryl iodides
and phenols or 2-naphthol. As shown in Table 2, both elec-
tron-rich (3e–3i) and electron-deficient (3j–3m) aryl iodides are
suitable substrates for this reaction, which provide the corre-
sponding diaryl ethers in good to excellent yields. A variety of
functional groups, which include methyl, alkoxyl, nitro, and
carbonyl groups, of aryl iodides are tolerant to these reaction
conditions well. The reactivity of phenols containing various
electron-withdrawing and electron-donating substrates was
compared using iodobenzene as an arylating agent (3a–3d).
We also observed that the coupling was favored by electron-
donating groups (3d). To our delight, the steric hindrance of
phenols is also favorable for this reaction. For example, when
2,4-di-tert-butylphenol was used as the substrate, the reaction
gave excellent yields (96%) in comparison with that of less-hin-
dered phenols (compare 3j and 3l). To the best of our knowl-
edge, the examples for Pd- or Cu-catalyzed diaryl ether
synthesis with substrates bearing a o-tert-butyl group were rela-
tively rare. In addition, we also tested reactions of alkyl alco-
hols with aryl iodides, and good yields were obtained (3n–3p).
The proposed catalytic system was further applied to
the coupling reaction of aryl bromides and phenols with
good results. As shown in Table 3, high yields were obtained
for aryl bromides with electron-withdrawing (5b–5d) and
Conclusion
In summary, we have developed an efficient, experimentally
simple, and economically attractive method for the
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Table 2 CuI-catalyzed coupling reaction of aryl iodides with phenols or 2-naphthola
Product
T (h)
Yb (%)
Product
T (h)
Yb (%)
12
90
5
95
12
83
12
89
15
15
74
99
7
75
96
12
12
9
72
70
6
71
63
24
10
20
60
60
24
24
73
71
a Reaction conditions: CuI (0.10 mmol), L1 (0.20 mmol), ArI (1.0 mmol), phenol (1.2 mmol), Cs2CO3 (2.5 mmol), DMF (1.5 mL), 100 °C. b Isolated
yield.
Cu-catalyzed synthesis of diaryl ethers from various aromatic
iodides, bromides, and chlorides using 2-carbomethoxy-
3-hydroxyquinoxaline-di-N-oxide as the ligand. This method
Experimental
General procedure A
shows broad functional-group tolerance and high selectivity A flask was charged with CuI (19.1 mg, 0.1 mmol, 10 mol%),
in the presence of multiple potentially reactive groups at L1 (47.2 mg, 0.2 mmol, 20 mol%), Cs2CO3 (812.5 mg,
moderate temperatures. This report provides an attractive 2.5 mmol), and any remaining solids (phenol and/or aryl
method for the synthesis of more complex diaryl ethers. halide). The flask was evacuated and backfilled with argon.
Efforts to extend the applications of these ligands to Aryl iodide (1.0 mmol, if liquid), phenol (1.5 mmol, if liquid),
other types of Cu-catalyzed coupling reactions are currently and DMF (1.5 mL) were added to the flask under an argon
underway in our laboratory and will be reported in due atmosphere. Then the mixture was stirred at 100 °C until com-
course.
plete consumption of starting material was monitored by TLC.
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Table 3 CuI-catalyzed coupling reaction of aryl bromide with phenols or 2-naphthola
Product
T (h)
Yb (%)
Product
T (h)
Yb (%)
20a
44
20d
71
12a
15a
93
92
20d
20d
87
54
11c
16a
98
92
20c
20c
55
77
a Reaction conditions: CuI (0.10 mmol), L1 (0.20 mmol), ArBr (1.0 mmol), phenol (1.2 mmol), Cs2CO3 (2.5 mmol), DMF (1.5 mL), 100 °C.
b Isolated yield. c Reaction was carried out at 110 °C. d Reaction was carried out at 100 °C for 12 h and 110 °C for 8 h.
After completion of the reaction, the mixture was diluted with (m, 1H), 7.48–7.26 (m, 6H), 7.17–7.14 (m, 1H), 7.10–7.08
ethyl acetate, passed through a fritted glass filter to remove the (m, 2H) ppm. MS (EI, m/z): 221 (M+ + 1).
inorganic salts and the solvent was removed with the aid of a
N-(4-Phenoxyphenyl)acetamide (3c). Following procedure A,
rotary evaporator. The residue was purified by column chrom- iodobenzene (0.112 mL, 1.0 mmol) was allowed to react
atography on silica gel using petroleum ether/ethyl acetate as with N-(4-hydroxyphenyl)acetamide (226.7 mg, 1.5 mmol) for
an eluent to provide the desired product.
15 h. The crude brown oil was purified by flash chromato-
Diphenyl ether (3a). Following procedure A, iodobenzene graphy on silica gel to provide 74% yield of the desired
(0.112 mL, 1.0 mmol) was allowed to react with phenol product as a brown solid. 1H NMR (400 MHz, CDCl3): δ 7.92
(0.134 mL, 1.5 mmol) for 12 h. The crude brown oil was puri- (br s, 1H), 7.48–7.45 (m, 2H), 7.32–7.28 (m, 2H), 7.08–7.07
fied by flash chromatography on silica gel to provide 90% yield (m, 1H), 6.97–6.94 (m, 4H), 2.15 (s, 3H) ppm. MS (EI, m/z):
of the desired product as a colorless liquid. 1H NMR 228 (M+ + 1).
(400 MHz, CDCl3): δ 7.36–7.32 (m, 4H), 7.12–7.08 (m, 2H),
7.02–7.00 (m, 4H) ppm. MS (EI, m/z): 171 (M+ + 1).
1-Methoxy-4-phenoxybenzene (3d). Following procedure A,
iodobenzene (0.112 mL, 1.0 mmol) was allowed to react with
2-Phenoxynaphthalene (3b). Following procedure A, iodo- 4-methoxyphenol (186.2 mg, 1.5 mmol) for 15 h. The crude
benzene (0.112 mL, 1.0 mmol) was allowed to react with brown oil was purified by flash chromatography on silica gel to
naphthalen-2-ol (216.3 mg, 1.5 mmol) for 12 h. The crude provide 99% yield of the desired product as a yellow oil.
brown oil was purified by flash chromatography on silica gel to 1H NMR (400 MHz, CDCl3): δ 7.34–7.30 (m, 2H), 7.09–7.05
provide 83% yield of the desired product as a white solid. (m, 1H), 7.03–6.97 (m, 4H), 6.93–6.90 (m, 2H), 3.82 (s, 3H)
1H NMR (400 MHz, CDCl3): δ 7.86–7.82 (m, 2H), 7.72–7.70 ppm. MS (EI, m/z): 201 (M+ + 1).
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Table 4 CuI-catalyzed coupling reaction of aryl chloride with phenols or 2-naphthola
Product
T (h)
Yb (%)
Product
T (h)
Yb (%)
5
84
12
72
8
97
12
99
12
12
95
94
12
12
87
91
12
89
a Reaction conditions: CuI (0.10 mmol), L1 (0.20 mmol), ArCl (1.0 mmol), phenol (1.2 mmol), Cs2CO3 (2.5 mmol), DMF (1.5 mL), 110 °C.
b Isolated yield.
1-Methyl-4-phenoxybenzene (3e). Following procedure A,
2-(p-Tolyloxy)naphthalene (3g). Following procedure A,
1-iodo-4-methylbenzene (141.2 mg, 1.0 mmol) was allowed to 1-iodo-4-methylbenzene (141.2 mg, 1.0 mmol) was allowed to
react with phenol (0.134 mL, 1.5 mmol) for 12 h. The crude react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for 10 h. The
brown oil was purified by flash chromatography on silica gel to crude brown oil was purified by flash chromatography on
provide 72% yield of the desired product as a yellow oil. silica gel to provide 60% yield of the desired product as a pale-
1H NMR (400 MHz, CDCl3): δ 7.35–7.31 (m, 2H), 7.17–7.15 yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.84–7.81 (m, 2H),
(m, 2H), 7.10–7.07 (m, 1H), 7.01–6.99 (m, 2H), 6.95–6.93 7.70–7.68 (m, 1H), 7.47–7.39 (m, 2H), 7.28–7.25 (m, 2H),
(m, 2H), 2.35 (s, 3H) ppm. MS (EI, m/z): 185 (M+ + 1).
N-(4-(p-Tolyloxy)phenyl)acetamide (3f). Following procedure (EI, m/z): 235 (M+ + 1).
7.20–7.17 (m, 2H), 7.01–6.98 (m, 2H), 2.37 (s, 3H) ppm. MS
A, 1-iodo-4-methylbenzene (141.2 mg, 1.0 mmol) was allowed
N-(4-(3,5-Dimethylphenoxy)phenyl)acetamide (3h). Follow-
to react with N-(4-hydroxyphenyl)acetamide (226.7 mg, ing procedure A, 1-iodo-3,5-dimethylbenzene (0.145 mL,
1.5 mmol) for 9 h. The crude brown oil was purified by flash 1.0 mmol) was allowed to react with N-(4-hydroxyphenyl)aceta-
chromatography on silica gel to provide 70% yield of the mide (226.7 mg, 1.5 mmol) for 20 h. The crude brown oil was
1
desired product as a brown solid. H NMR (400 MHz, CDCl3): purified by flash chromatography on silica gel to provide 60%
δ 7.58 (br s, 1H), 7.42 (dt, J = 7.2, 2.0 Hz, 2H), 7.11 (d, J = 8.0 yield of the desired product as a pale-yellow oil. 1H NMR
Hz, 2H), 6.93 (dt, J = 7.2, 2.0 Hz, 2H), 6.87 (d, J = 8.4 Hz, 2H), (400 MHz, CDCl3): δ 7.44 (d, J = 8.8 Hz, 2H), 6.95 (d, J = 8.8 Hz,
2.32 (s, 3H), 2.15 (s, 3H) ppm. MS (EI, m/z): 242 (M+ + 1).
2H), 6.72 (s, 1H), 6.59 (s, 2H), 2.27 (s, 6H), 2.17 (s, 3H) ppm.
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Ethyl 4-(naphthalen-2-yloxy)benzoate (3k). Following pro-
cedure A, ethyl 4-iodobenzoate (276.0 mg, 1.0 mmol) was
allowed to react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for
7 h. The crude brown oil was purified by flash chromato-
graphy on silica gel to provide 75% yield of the desired
product as a brown oil. 1H NMR (400 MHz, CDCl3): δ 8.05–8.03
(m, 2H), 7.89–7.85 (m, 2H), 7.76–7.74 (m, 1H), 7.51–7.44
(m, 3H), 7.27–7.25 (m, 1H), 7.06–7.04 (m, 2H), 4.37 (q, J =
14.4 Hz, 2H), 1.39 (t, J = 7.2 Hz, 3H) ppm. MS (EI, m/z):
293 (M+ + 1).
2,4-Di-tert-butyl-1-(4-nitrophenoxy)benzene (3l). Following
procedure A, 1-iodo-4-nitrobenzene (249 mg, 1.0 mmol) was
allowed to react with 2,4-di-tert-butylphenol (206.3 mg,
1.5 mmol) for 12 h. The crude brown oil was purified by flash
chromatography on silica gel to provide 96% yield of the
1
desired product as a colorless oil. H NMR (400 MHz, CDCl3):
δ 8.22–8.18 (m, 2H), 7.47–7.46 (m, 1H), 7.24–7.21 (m, 1H),
7.03–6.99 (m, 2H), 6.82–6.80 (m, 1H), 1.36 (s, 9H), 1.35 (s, 9H)
ppm. 13C NMR (100 MHz, CDCl3): δ 163.7, 151.1, 148.0, 142.5,
140.9, 125.9, 124.7, 124.3, 121.1, 117.2, 34.9, 34.7, 31.5,
30.4 ppm. MS (EI, m/z): 328 (M+ + 1). HRMS (ESI): calcd for
C20H25NO3Na [MNa+] 350.1732, found 350.1729.
1-Methoxy-4-(4-nitrophenoxy)benzene (3m). Following pro-
cedure A, 1-iodo-4-nitrobenzene (249 mg, 1.0 mmol) was
allowed to react with 4-methoxyphenol (186.2 mg, 1.5 mmol)
for 6 h. The crude brown oil was purified by flash chromato-
graphy on silica gel to provide 71% yield of the desired
product as a white solid. 1H NMR (400 MHz, CDCl3): δ 8.17
(d, J = 9.2 Hz, 2H), 7.02 (d, J = 9.2 Hz, 2H), 6.97–6.94 (m, 4H),
3.83 (s, 3H) ppm. MS (EI, m/z): 246 (M+ + 1).
Fig. 2 Proposed mechanism.
4-Ethoxyanisole (3n). Following procedure A, 4-iodoanisole
(234.0 mg, 1.0 mmol) was allowed to react with ethanol
(0.087 mL, 1.5 mmol) for 24 h. The crude brown oil was puri-
fied by flash chromatography on silica gel to provide 63% yield
of the desired product as a white solid. 1H NMR (400 MHz,
CDCl3): δ 6.67–6.65 (m, 4H), 3.98 (q, J = 7.2 Hz, 2H), 3.75
(s, 3H), 1.21 (t, J = 7.2 Hz, 3H) ppm. 13C NMR (100 MHz,
CDCl3): δ 153.8, 153.5, 115.4, 114.6, 64.7, 55.7, 15.8 ppm.
4-n-Butoxyanisole (3o). Following procedure A, 4-iodoani-
sole (234.0 mg, 1.0 mmol) was allowed to react with n-butanol
(0.137 mL, 1.5 mmol) for 24 h. The crude brown oil was puri-
fied by flash chromatography on silica gel to provide 73% yield
of the desired product as a colorless liquid. 1H NMR
(400 MHz, CDCl3): δ 6.68–6.65 (m, 4H), 3.93 (t, J = 6.8 Hz, 2H),
3.76 (s, 3H), 1.78–1.70 (m, 2H), 1.62–1.52 (m, 2H), 0.92 (t, J =
7.6 Hz, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 153.8, 153.5,
115.4, 114.6, 68.6, 55.3, 34.9, 18.9, 13.8 ppm.
4-Isopropyloxyanisole (3p). Following procedure A, 4-iodo-
anisole (234.0 mg, 1.0 mmol) was allowed to react with isopro-
panol (0.115 mL, 1.5 mmol) for 24 h. The crude brown oil was
purified by flash chromatography on silica gel to provide 71%
yield of the desired product as a colorless liquid. 1H NMR
(400 MHz, CDCl3): δ 6.88–6.84 (m, 4H), 4.44–4.35 (m, 1H),
3.75 (s, 3H), 1.38 (d, J = 6.4 Hz, 6H) ppm. 13C NMR
(100 MHz, CDCl3): δ 153.5, 153.3, 115.4, 114.6, 64.9, 55.3,
25.3 ppm.
MS (EI, m/z): 256 (M+ + 1). 13C NMR (100 MHz, CDCl3): δ 168.3,
157.5, 153.7, 139.6, 133.1, 124.8, 121.7, 119.6, 116.1, 24.4,
21.3 ppm. HRMS (ESI): calcd for C16H17NO2Na [MNa+]
278.1157, found 278.1153.
2-(3,5-Dimethylphenoxy)naphthalene (3i). Following proce-
dure A, 1-iodo-3,5-dimethylbenzene (0.145 mL, 1.0 mmol) was
allowed to react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for
5 h. The crude brown oil was purified by flash chromatography
on silica gel to provide 95% yield of the desired product as a
1
colorless oil. H NMR (400 MHz, CDCl3): δ 8.40 (dt, J = 9.2, 2.8
Hz, 2H), 7.73–7.65 (m, 4H), 7.38 (d, J = 3.6 Hz, 1H), 7.33–7.29
(m, 1H), 7.27–7.23 (m, 1H), 6.78 (dd, J = 3.4, 0.8 Hz, 1H) ppm.
13C NMR (125 MHz, CDCl3): δ 157.3, 155.5, 139.7, 134.5, 130.2,
129.8, 127.8, 127.2, 126.5, 125.3, 124.6, 120.2, 116.9, 114.2,
21.3 ppm. MS (EI, m/z): 249 (M+ + 1). HRMS (ESI): calcd for
C18H17O [MH+] 249.1279, found 249. 1272.
1-Nitro-4-phenoxybenzene (3j). Following procedure A,
1-iodo-4-nitrobenzene (249 mg, 1.0 mmol) was allowed to react
with phenol (0.134 mL, 1.5 mmol) for 12 h. The crude brown
oil was purified by flash chromatography on silica gel to
provide 89% yield of the desired product as a yellow solid.
1H NMR (400 MHz, CDCl3): δ 8.20 (d, J = 9.2 Hz, 2H), 7.46–7.42
(m, 2H), 7.28–7.24 (m, 1H), 7.09 (m, 2H), 7.01 (d, J = 9.2 Hz,
2H) ppm. MS (EI, m/z): 216 (M+ + 1).
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General procedure B
was allowed to react with naphthalen-2-ol (216.3 mg,
1.5 mmol) for 16 h at 100 °C. The crude brown oil was purified
by flash chromatography on silica gel to provide 92% yield of
the desired product as a yellow oil. 1H NMR (400 MHz, CDCl3):
δ 7.86–7.83 (m, 2H), 7.74–7.71 (m, 1H), 7.49–7.40 (m, 2H),
7.36–7.35 (m, 1H), 7.29–7.24 (m, 2H), 6.72–6.65 (m, 3H), 3.79
(s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 161.2, 158.6, 155.0,
134.5, 130.4, 130.2, 129.9, 127.8, 127.2, 126.6, 124.8, 120.1,
114.5, 111.3, 109.3, 105.2, 55.4 ppm. MS (EI, m/z): 251 (M+ + 1).
HRMS (ESI): calcd for C17H15O2 [MH+] 251.1072, found
251.1070.
An oven-dried Schlenk tube equipped with a Teflon valve
(Kontes) was charged with a magnetic stir bar, CuI (19.1 mg,
0.1 mmol, 10 mol%), the L1 (47.2 mg, 0.2 mmol, 20 mol%)
and the inorganic base (2.5 mmol): Cs2CO3 (812.5 mg). Any
remaining solids (phenol and/or aryl bromide) were added at
this point. The tube was evacuated and backfilled with argon
(this procedure was repeated three times). Under a counterflow
of argon, phenol (if liquid), aryl bromide (if liquid) and DMF
(1.5 mL) were added using a syringe. Finally, the tube was
sealed and the mixture was heated at the indicated tempera-
ture (100 °C–110 °C) for the indicated period of time. Upon
completion of the reaction, the mixture was allowed to cool to
room temperature and then was diluted with ethyl acetate,
passed through a fritted glass filter to remove the inorganic
salts and the solvent was removed with the aid of a rotary evap-
orator. The residue was purified by column chromatography
on silica gel and the product was dried under vacuum for at
least 1 h.
N-(4-(4-Acetylphenoxy)phenyl)acetamide (5f). Following pro-
cedure B, 1-(4-bromophenyl)ethanone (199.0 mg, 1.0 mmol)
was allowed to react with N-(4-hydroxyphenyl)acetamide
(226.7 mg, 1.5 mmol) at 100 °C for 12 h and 110 °C for 8 h.
The crude brown oil was purified by flash chromatography on
silica gel to provide 71% yield of the desired product as a
1
white solid. H NMR (400 MHz, CDCl3): δ 8.05 (br s, 1H), 7.90
(d, J = 8.8 Hz, 2H), 7.54 (d, J = 9.2 Hz, 2H), 6.99 (d, J = 8.8 Hz,
2H), 6.94 (d, J = 8.8 Hz, 2H), 2.56 (s, 3H), 2.17 (s, 3H) ppm. MS
(EI, m/z): 270 (M+ + 1).
Diphenyl ether (5a/3a). Following procedure B, bromo-
benzene (0.105 mL, 1.0 mmol) was allowed to react with phenol
(0.134 mL, 1.5 mmol) for 20 h at 100 °C. The crude brown oil
was purified by flash chromatography on silica gel to provide
44% yield of the desired product as a colorless oil. 1H NMR
(400 MHz, CDCl3): δ 7.36–7.32 (m, 4H), 7.12–7.08 (m, 2H),
7.02–7.00 (m, 4H) ppm. MS (EI, m/z): 171 (M+ + 1).
1-(4-(4-Methoxyphenoxy)phenyl)ethanone
(5g). Following
procedure B, 1-(4-bromophenyl)ethanone (199.0 mg,
1.0 mmol) was allowed to react with 4-methoxyphenol
(186.2 mg, 1.5 mmol) at 100 °C for 12 h and 110 °C for 8 h.
The crude brown oil was purified by flash chromatography on
silica gel to provide 87% yield of the desired product as a
yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.92–7.90 (m, 2H),
7.02–7.00 (m, 2H), 6.95–6.91 (m, 4H) ppm. MS (EI, m/z): 243
(M+ + 1).
1-(4-(2,4-Di-tert-butylphenoxy)phenyl)ethanone (5h). Follow-
ing procedure B, 1-(4-bromophenyl)ethanone (199.0 mg,
1.0 mmol) was allowed to react with 2,4-di-tert-butylphenol
(206.3 mg, 1.5 mmol) at 100 °C for 12 h and 110 °C for 8 h.
The crude brown oil was purified by flash chromatography on
silica gel to provide 54% yield of the desired product as a col-
orless oil. 1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 8.8 Hz,
2H), 7.45 (d, J = 2.4 Hz, 1H), 7.18 (d, J = 2.4 Hz, 1H), 6.99
(d, J = 8.8 Hz, 2H), 7.80 (d, J = 8.4 Hz, 1H), 2.57 (s, 3H), 1.38
(s, 9H), 1.34 (s, 9H) ppm. 13C NMR (100 MHz, CDCl3): δ 162.5,
151.7, 147.1, 140.7, 130.5, 124.5, 124.1, 120.9, 117.2, 34.9, 34.6,
31.6, 31.5, 30.3, 29.7, 26.3 ppm. MS (EI, m/z): 325 (M+ + 1).
HRMS (ESI): calcd for C22H28O2Na [MNa+] 347.1987, found
347.1984.
1-Methoxy-3-phenoxybenzene (5i). Following procedure B,
1-bromo-3-methoxybenzene (0.126 mL, 1.0 mmol) was allowed
to react with phenol (0.134 mL, 1.5 mmol) for 20 h at 110 °C.
The crude brown oil was purified by flash chromatography on
silica gel to provide 55% yield of the desired product as a
brown oil. 1H NMR (400 MHz, CDCl3): δ 7.38–7.34 (m, 2H),
7.28–7.22 (m, 1H), 7.15–7.11 (m, 1H), 7.06–7.04 (m, 2H),
6.69–6.67 (m, 1H), 6.62–6.60 (m, 2H), 3.80 (s, 3H) ppm. MS (EI,
m/z): 201 (M+ + 1).
2-(4-Nitrophenoxy)naphthalene (5b). Following procedure B,
1-bromo-4-nitrobenzene (202.0 mg, 1.0 mmol) was allowed to
react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for 12 h at
100 °C. The crude brown oil was purified by flash chromato-
graphy on silica gel to provide 93% yield of the desired
product as a yellow oil. 1H NMR (400 MHz, CDCl3): δ 8.24–8.20
(m, 2H), 7.94–7.88 (m, 2H), 7.81–7.78 (m, 1H), 7.56–7.48
(m, 3H), 7.27–7.24 (m, 1H), 7.09–7.05 (m, 2H) ppm. MS
(EI, m/z): 266 (M+ + 1).
1-(4-(Naphthalen-2-yloxy)phenyl)ethanone (5c). Following
procedure B, 1-(4-bromophenyl)ethanone (199.0 mg,
1.0 mmol) was allowed to react with naphthalen-2-ol
(216.3 mg, 1.5 mmol) for 15 h at 100 °C. The crude brown oil
was purified by flash chromatography on silica gel to provide
92% yield of the desired product as a brown solid. 1H NMR
(400 MHz, CDCl3): δ 7.99–7.95 (m, 2H), 7.90–7.86 (m, 2H),
7.77–7.75 (m, 1H), 7.53–7.45 (m, 3H), 7.28–7.25 (m, 1H),
7.08–7.05 (m, 2H), 2.59 (s, 3H) ppm. MS (EI, m/z): 263 (M+ + 1).
N-(4-(4-Nitrophenoxy)phenyl)acetamide (5d). Following pro-
cedure B, 1-bromo-4-nitrobenzene (202.0 mg, 1.0 mmol) was
allowed to react with N-(4-hydroxyphenyl)acetamide (226.7 mg,
1.5 mmol) for 11 h at 110 °C. The crude brown oil was purified
by flash chromatography on silica gel to provide 98% yield of
the desired product as a yellow solid. 1H NMR (400 MHz,
CDCl3): δ 8.17 (d, J = 9.2 Hz, 2H), 7.69 (br s, 1H), 7.57
(d, J = 8.8 Hz, 2H), 7.03 (d, J = 8.8 Hz, 2H), 6.97 (d, J = 9.2 Hz,
2H), 2.20 (s, 3H) ppm. MS (EI, m/z): 273 (M+ + 1).
1-Methoxy-3-phenoxybenzene (5j). Following procedure B,
2-(3-Methoxyphenoxy)naphthalene
(5e). Following
pro- 1-bromo-3-methoxybenzene (0.126 mL, 1.0 mmol) was allowed
cedure B, 1-bromo-3-methoxybenzene (0.126 mL, 1.0 mmol) to react with phenol (4-methoxyphenol; 186.2 mg, 1.5 mmol)
1508 | Org. Biomol. Chem., 2013, 11, 1502–1510
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for 20 h at 110 °C. The crude brown oil was purified by flash by flash chromatography on silica gel to provide 89% yield of
chromatography on silica gel to provide 77% yield of the the desired product as a yellow oil. 1H NMR (400 MHz, CDCl3):
desired product as a yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.95–7.93 (m, 1H), 7.47–7.43 (m, 2H), 7.21–7.18 (m, 1H),
δ 7.21–7.17 (m, 1H), 7.01–6.99 (m, 2H), 6.90–6.88 (m, 2H), 7.14–7.11 (m, 1H), 6.96–6.94 (m, 1H), 6.77–6.75 (m, 1H), 1.42
6.61–6.59 (m, 1H), 6.53–6.52 (m, 2H), 3.81 (s, 3H), 3.77 (s, 3H) (s, 9H), 1.35 (s, 9H) ppm. MS (EI, m/z): 328 (M+ + 1).
ppm. MS (EI, m/z): 231 (M+ + 1).
8-(2-Nitrophenoxy)quinoline (7f). Following procedure C,
1-chloro-2-nitrobenzene (236.3 mg, 1.0 mmol) was allowed to
react with quinolin-8-ol (217.8 mg, 1.5 mmol) for 12 h at
General procedure C
An oven-dried Schlenk tube equipped with a Teflon valve 110 °C. The crude brown oil was purified by flash chromato-
(Kontes) was charged with a magnetic stir bar, CuI (19.1 mg, graphy on silica gel to provide 72% yield of the desired
0.1 mmol, 10 mol%), the L1 (47.2 mg, 0.2 mmol, 20 mol%) product as a yellow oil. 1H NMR (400 MHz, CDCl3): δ 8.89
and the inorganic base (2.5 mmol): Cs2CO3 (812.5 mg). Any (d, J = 4.0 Hz, 1H), 8.17 (d, J = 8.4 Hz, 1H), 8.01 (d, J = 8.0 Hz,
remaining solids (phenol and/or aryl chloride) were added at 1H), 7.62 (d, J = 8.4 Hz, 1H), 7.48–7.42 (m, 3H), 7.22–7.16
this point. The tube was evacuated and backfilled with argon (m, 2H), 6.97 (d, J = 8.4 Hz, 1H) ppm. MS (EI, m/z): 267
(this procedure was repeated three times). Under a counterflow (M+ + 1).
of argon, phenol (if liquid), aryl chloride (if liquid) and DMF
8-(4-Nitrophenoxy)quinoline (7g). Following procedure C,
(1.5 mL) were added using a syringe. Finally, the tube was 1-chloro-4-nitrobenzene (236.3 mg, 1.0 mmol) was allowed to
sealed and the mixture was heated at the indicated tempera- react with quinolin-8-ol (217.8 mg, 1.5 mmol) for 12 h at
ture (110 °C) for the indicated period of time. Upon com- 110 °C. The crude brown oil was purified by flash chromato-
pletion of the reaction, the mixture was allowed to cool to graphy on silica gel to provide 99% yield of the desired
room temperature and then was diluted with ethyl acetate, product as a yellow oil. 1H NMR (400 MHz, CDCl3): δ 8.89–8.88
passed through a fritted glass filter to remove the inorganic (m, 1H), 8.26–8.24 (m, 1H), 8.17 (d, J = 8.8 Hz, 2H), 7.77–7.75
salts and the solvent was removed with the aid of a rotary evap- (m, 1H), 7.59–7.55 (m, 1H), 7.49–7.46 (m, 1H), 7.44–7.42
orator. The residue was purified by column chromatography (m, 1H), 7.02 (d, J = 9.2 Hz, 2H) ppm. MS (EI, m/z): 267
on silica gel and the product was dried under vacuum for at (M+ + 1).
least 1 h.
2-(4-Nitrophenoxy)naphthalene (7h/5b). Following pro-
1-Nitro-2-phenoxybenzene (7b). Following procedure C, cedure C, 1-chloro-4-nitrobenzene (236.3 mg, 1.0 mmol) was
1-chloro-2-nitrobenzene (236.3 mg, 1.0 mmol) was allowed to allowed to react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for
react with phenol (0.134 mL, 1.5 mmol) for 8 h at 110 °C. The 12 h at 110 °C. The crude brown oil was purified by flash
crude brown oil was purified by flash chromatography on chromatography on silica gel to provide 87% yield of the
silica gel to provide 97% yield of the desired product as a desired product as a yellow oil. 1H NMR (400 MHz, CDCl3):
1
yellow solid. H NMR (400 MHz, CDCl3): δ 7.95–7.93 (m, 1H), δ 8.24–8.20 (m, 2H), 7.94–7.88 (m, 2H), 7.81–7.78 (m, 1H),
7.52–7.48 (m, 1H), 7.40–7.36 (m, 2H), 7.21–7.17 (m, 2H), 7.56–7.48 (m, 3H), 7.27–7.24 (m, 1H), 7.09–7.05 (m, 2H) ppm.
7.06–6.99 (m, 3H) ppm. MS (EI, m/z): 216 (M+ + 1).
MS (EI, m/z): 266 (M+ + 1).
N-(4-(2-Nitrophenoxy)phenyl)acetamide (7c). Following pro-
2,4-Di-tert-butyl-1-(4-nitrophenoxy)benzene (7i). Following
cedure C, 1-chloro-2-nitrobenzene (236.3 mg, 1.0 mmol) was procedure C, 1-chloro-4-nitrobenzene (236.3 mg, 1.0 mmol)
allowed to react with N-(4-hydroxyphenyl)acetamide (226.7 mg, was allowed to react with 2,4-di-tert-butylphenol (206.3 mg,
1.5 mmol) for 12 h at 110 °C. The crude brown oil was purified 1.5 mmol) for 12 h at 110 °C. The crude brown oil was purified
by flash chromatography on silica gel to provide 95% yield of by flash chromatography on silica gel to provide 91% yield of
the desired product as a yellow oil. 1H NMR (400 MHz, CDCl3): the desired product as a yellow oil. 1H NMR (400 MHz, CDCl3):
δ 7.93–7.91 (m, 1H), 7.76 (m, 1H), 7.51–7.45 (m, 3H), 7.19–7.15 δ 8.22–8.18 (m, 2H), 7.47–7.46 (m, 1H), 7.24–7.21 (m, 1H),
(m, 1H), 6.98–6.94 (m, 3H), 2.16 (s, 3H) ppm. MS (EI, m/z): 273 7.03–6.99 (m, 2H), 6.82–6.80 (m, 1H), 1.36 (s, 9H), 1.35 (s, 9H)
(M+ + 1).
ppm. 13C NMR (100 MHz, CDCl3): δ 163.7, 151.1, 148.0, 142.5,
2-(2-Nitrophenoxy)naphthalene (7d). Following procedure 140.9, 125.9, 124.7, 124.3, 121.1, 117.2, 34.9, 34.7, 31.5,
C, 1-chloro-2-nitrobenzene (236.3 mg, 1.0 mmol) was allowed 30.4 ppm. MS (EI, m/z): 328 (M+ + 1). HRMS (ESI): calcd for
to react with naphthalen-2-ol (216.3 mg, 1.5 mmol) for 12 h at C20H25NO3Na [MNa+] 350.1732, found 350.1729.
110 °C. The crude brown oil was purified by flash chromato-
graphy on silica gel to provide 94% yield of the desired
product as a yellow oil. 1H NMR (400 MHz, CDCl3): δ 8.01–7.99
(m, 1H), 7.90–7.84 (m, 2H), 7.75–7.73 (m, 1H), 7.54–7.44
Acknowledgements
(m, 3H), 7.38 (m, 1H), 7.30–7.21 (m, 2H), 7.08–7.06 (m, 1H)
ppm. MS (EI, m/z): 266 (M+ + 1).
We thank the National Natural Science Foundation (Grant
2,4-Di-tert-butyl-1-(2-nitrophenoxy)benzene (7e). Following No. 20972160 and 21172220), the National Basic Research
procedure C, 1-chloro-2-nitrobenzene (236.3 mg, 1.0 mmol) Program of China (Grant No. 2009CB940900), and CSA-Guang-
was allowed to react with 2,4-di-tert-butylphenol (206.3 mg, dong Joint Foundation (Grant No. 2011B090300069) for their
1.5 mmol) for 12 h at 110 °C. The crude brown oil was purified financial support.
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Organic & Biomolecular Chemistry
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This journal is © The Royal Society of Chemistry 2013