Regioselective ortho-nitration of N-phenyl carboxamides and primary anilines using bismuth nitrate/acetic anhydride

Article abstract of DOI:10.1016/j.tet.2013.08.076

An efficient and one-pot synthetic method for the regioselective ortho-nitration of the N-phenyl carboxamides and primary anilines has been developed by using bismuth nitrate and acetic anhydride as the nitrating reagents. Reaction proceeds at room temperature and results in corresponding ortho-nitrated products in moderate to excellent yields. This method provides an operationally simple, regioselective, and efficient access to synthesize o-nitro anilines under the mild conditions.

Full text of DOI:10.1016/j.tet.2013.08.076

Tetrahedron 69 (2013) 9422e9427
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Regioselective ortho-nitration of N-phenyl carboxamides and
primary anilines using bismuth nitrate/acetic anhydride
*
Yang Lu, Yaming Li , Rong Zhang, Kun Jin, Chunying Duan
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 May 2013
Received in revised form 21 August 2013
Accepted 30 August 2013
Available online 5 September 2013
An efficient and one-pot synthetic method for the regioselective ortho-nitration of the N-phenyl car-
boxamides and primary anilines has been developed by using bismuth nitrate and acetic anhydride as
the nitrating reagents. Reaction proceeds at room temperature and results in corresponding ortho-ni-
trated products in moderate to excellent yields. This method provides an operationally simple, re-
gioselective, and efficient access to synthesize o-nitro anilines under the mild conditions.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
ortho-Nitration
Aromatic amines
Bismuth nitrate
Regioselectivity
Synthetic methods
1. Introduction
and the use of directing groups. In addition, there are few reports
on the selective nitration of highly activated aromatics, such as
Aromatic nitro compounds have been widely utilized as the
important fine chemical intermediates for the generation of ex-
plosives, dyes and pharmaceuticals.1 Therefore, the nitration of
aromatics is probably one of the most important processes in or-
ganic chemical industry. The mixed acid system (H2SO4/HNO3) as
the nitrating reagent usually is widely used in the classical elec-
trophilic nitration of the arenes. However, the isomeric mixtures of
nitrated products are often obtained.2 Furthermore, most existing
nitrating reagents are strong oxidants, which limit their application
scope for some easily oxidized substrates, such as anilines and
phenols. Therefore, a mild and operationally simple method for
regioselective nitration has been the focus of the recent researches.
Some notable progresses have been made toward regioselective
nitration in (hetero)arenes over the past several years,3 including
the use of zeolites,4 ipso-nitration of arylboronic acids via inorganic
nitrate5 or tert-butyl nitrite,6 the transition-metal-catalyzed cross-
coupling of (hetero)aryl halides with nitrite salts,7 and the
transition-metal-catalyzed ortho-nitration of aromatic CeH bonds
aided by using a nitrogen donor as the directing group.8 Although
these nitration protocols under mild conditions could improve the
regioselectivity significantly, there are still some limitations, such
as poor substrate scope, expensive catalyst, prefunctionalization
anilines.9
o-Nitroanilines are key intermediates used in the synthesis of
valuable compounds, such as the benzimidazoles10 and 1,2-
diamines.11 Typically, the nitration of anilines can be achieved in
a two-step process: the acetylation of anilines and subsequent ni-
tration with mixed acid. However, mainly para-nitrated product is
obtained through nitration of acetanilide.12 In the past few years,
several methods for ortho-nitration reaction in the field of
transition-metal-free ortho-selective aromatic nitration reactions
has been developed by Suzuki group,13 using phenyl alkyl ethers
and phenyl acetic esters as directing groups. However, using acet-
amido as a directing group, the ortho/para ratio of the nitration of
acetanilides with nitrogen dioxide is 4.4 (Scheme 1).14 Thus, to
develop a methodology enabling ortho-selective nitration of ani-
lines with efficient, experimentally simple, economical and
a broader substrate scope would be a challenging scientific task. In
recent years, various nitrate salts, such as (NH4)2Ce(NO3)6,9a 15
,
Fe(NO3)3$9H2O,16 Ca(NO3)2,17 Ni(NO3)2$6H2O,18 Mg(NO3)2$6H2O,19
21
AgNO3,20 and (Me4 N)NO3 have been utilized as efficient nitrat-
ing agents. The non-regioselective nitration of phenols with bis-
muth nitrate (Bi(NO3)3$5H2O)22 as nitrating reagent has been
reported by Sun and co-workers.23 During our research for a mild
and regioselective nitration of aromatic primary amines, employing
bismuth nitrate with addition of acetic anhydride, we found that
mainly the ortho-nitration of N-phenyl carboxamides was achieved
(Scheme 1). Herein, we report a convenient and mild procedure for
* Corresponding author. Tel./fax: þ86 411 84986295; e-mail address: ymli@dlu-
t.edu.cn (Y. Li).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.076

Y. Lu et al. / Tetrahedron 69 (2013) 9422e9427
9423
the synthesis of o-nitroacetanilides in a one-pot reaction with good
regioselectivity.
EtOAc, THF, and CH3CN, led bad conversion (Table 1, entries 5e7).
Nitration did not take place in much polar solvents, such as DMSO
and t-BuOH (Table 1, entries 8 and 9). The solvent effect on the
nitration may be explained by the nitronium ionesolvent or sub-
strateesolvent interactions (such as protonation, hydrogen bond-
ing and solvation). Secondly, the effect of amount of acetic
anhydride was investigated. When employed 4.0 equiv Ac2O, 84% of
starting material (1a) was left (Table 1, entry 10). However, when
5.0 equiv even 6.0 equiv Ac2O was employed, the reaction could
proceed smoothly and give 2a in 89% or 92% yields, respectively
(Table 1, entries 11 and 12). A number of other nitrate salts, such as
Cu(NO3)2$3H2O, Ca(NO3)2$4H2O, Ni(NO3)2$6H2O, AgNO3, KNO3,
and NaNO3 were also examined, no or trace amount of nitrated
product was formed.26 This result may suggest that bismuth nitrate
acted here as both a reagent and a Lewis acid catalyst.27 Decreasing
the temperature to 0 ꢀC, the yield of 2a is 92% after 12 h reaction
(Table 1, entry 13). From the results shown above, the optimal ni-
tration conditions were as follows: 1.0 equiv of Bi(NO3)3$5H2O and
6.0 equiv of acetic anhydride with DCM as solvent (Table 1, entry
12).
With the optimized reaction conditions in hand, we explored
the scope of directing groups at the N-phenyl carboxamides (Table
2). Besides the acetamido group, the nitration of other amido
moieties as a directing group were tested. The nitration of sub-
strates bearing iso-propylamido and phenylamido groups gave the
desired ortho-nitrated products 2b and 2d in good yields (Table 2,
entries 2 and 4). Since two aromatic rings of the N-phenyl-
benzamide (1d) show different electron densities, the nitration
mainly took place at the aromatic ring bonded at the nitrogen atom,
while no nitrated product was observed at the electron-poor aro-
matic ring bearing the carbonyl group. This could be a proof of
Bi(NO3)3$5H2O/Ac2O as a relatively mild nitrating system. As pre-
dicted, the nitration of strong electron-withdrawing N-tri-
fluoroacetyl aniline gave relatively lower yield of 43% (Table 2,
entry 3). The nitration of N-methylacetanilide resulted in a mixture
Scheme 1. Synthesis of o-nitroacetanilides in a one-pot reaction.
2. Results and discussion
When studying metal-catalyzed ortho-nitration of CeH bond of
acetanilide with the acetamino group as a directing group, we were
gratified to find that ortho-nitration of acetanilide (1a) took place
via the 1.0 equiv of Bi(NO3)3$5H2O in the presence of 10.0 equiv
acetic anhydride in 1,2-dichloroethane (DCE) at room temperature
and generated the o-nitroacetanilide (2a) in 89% yield and para-
nitrated product (2a0) in 11% yield, respectively (determined and
confirmed by GC and GCeMS, 1H NMR, Table 1, entry 1). The ortho/
para ratios of nitroacetanilide isomers obtained were much higher
than those found in the classical HNO3eAc2O system.24 Notably,
replacing acetic anhydride by acetic acid, only trace amount of
nitrated products were obtained (Table 1, entry 2), indicating that
acetyl nitrate (AcONO2)25 was generated in situ by mixing bismuth
nitrate with acetic anhydride, then the active nitrating species
nitronium ions (NOþ2 ) were formed and then the electrophilic ar-
omatic substitution took place.
Table 1
Optimization of nitration conditionsa
Table 2
Regioselective ortho-nitration of N-phenyl carboxamidesa
Entry
Substrate
Product
Yield (%)b
o:p ratioc
Entry Solvent
Additive (equiv) T (ꢀC) Time (h) GC yield (%)
1a 2a
89 11
2a0
1
2
3
DCE
DCE
DCM
Ac2O [10]
AcOH [10]
Ac2O [10]
23
23
23
23
23
23
23
23
23
23
23
23
0
3
0
1
2
3
4
5
1a (R¼Me)
1b (R¼iPr)
2a
2b
2c
2d
2e
81
84
43
81
91
11.5:1
19:1
1.3:1
13.3:1
49:1
3
2.5
4.5
98
0
0
1
91
75 25
1
9
1c (R¼CF3)
1d (R¼Ph)
4
Cyclohexane Ac2O [10]
5
6
EtOAc
THF
Ac2O [10]
Ac2O [10]
Ac2O [10]
Ac2O [10]
Ac2O [10]
Ac2O [4]
Ac2O [5]
Ac2O [6]
Ac2O [6]
14
26
90
96
100
100
84
0
66
8
4
0
0
8
2
0
0
0
0
1e (R¼4-ClC6C4
14
14
14
14
6
6
2.5
12
7
8
9
10
11
12
13
CH3CN
DMSO
t-BuOH
DCM
DCM
DCM
6
7
93d
40
1.3:1
0.9:1
16
89 11
0
0
92b
92
8
8
DCM
a
All reactions were run using 1.0 equiv of Bi(NO3)3$5H2O and with a starting
material concentration of 0.1 M.
b
Isolated yield¼81%.
Above experimental results prompted us to investigate this
model reaction in more detail. Firstly, different solvents were
screened (Table 1, entries 3e9). It was found that dichloromethane
(DCM) gave 2a in yield of 91%. Nonpolar solvent, cyclohexane,
resulted in a lower regioselectivity due to a weak interaction be-
tween the hydrogen atom of the amide group with the nitro group
(see Scheme 3 for details). The use of some polar solvents, such as
a
Reaction conditions: N-Phenyl carboxamide (0.2 mmol), Bi(NO3)3$5H2O
(0.2 mmol), Ac2O (1.2 mmol) and DCM (1.0 mL) were stirred at 23 ꢀC for 2.5e5 h
under air.
b
Isolated yield.
c
o:p ratio is determined by GC analysis of the crude reaction mixtures.
d
Total yield, the o/p ratio is calculated by 1H NMR. Bi(NO3)3$5H2O (0.35 mmol),
Ac2O (2.1 mmol).

9424
Y. Lu et al. / Tetrahedron 69 (2013) 9422e9427
Table 3
of regioisomers with lower selectivity (Table 2, entry 6). Such
a decrease in ortho-selectivity could attribute to the following
reasons. First, methyl group at the amide may force it to rotate out
of the plane of the phenyl group. This may render the intra-
molecular nitro-transfer step less favorable (intermediate 1ab in
Scheme 3), thus favoring the competing intermolecular nitration
process. Second, the N-methyl group may render the phenyl group
more electron-rich, also favoring the undesired intermolecular ni-
tration process. The nitration of the N-phenylmaleimide with
strong steric hindrance and poor electron generated N-(o-nitro-
phenyl) maleimide (2g) in 40% yield (Table 2, entry 7).
Scope of primary anilinesa
Entry Substrate
Product
Yield (%)b o:p ratioc
1
94
19:1
Since the aniline could be acetylated with acetic anhydride, we
attempted to make the acetylation and nitration in a ‘one-pot’ using
bismuth nitrate/acetic anhydride as a mild nitrating reagent. It was
pleased to find that the o-nitroacetanilide (2a) was obtained in 94%
yield (Table 3, entry 1). Considering amino group consumed acetic
anhydride during the acetylation, the amount of Ac2O was also
examined.26 We further explored the substrate scope of the
substituted primary anilines. A variety of functional groups were
well tolerated under the reaction conditions. When primary ani-
lines with methyl, chloro, bromo, and methoxy activating groups at
the para-position, the ortho-nitrated products (2iel) were obtained
in excellent yields (Table 3, entries 2e5). Even p-acetyl aniline gave
the o-nitrated product in yield of 74% (Table 3, entry 6). Un-
fortunately, when a strong electron-withdrawing nitro group
existed at para-position, only trace amount of desired product was
formed (2n) even at higher temperatures or longer reaction time,
which could attribute to the deactivating effect on the electrophilic
aromatic substitution reaction. Next we explored the ortho-
substituted anilines. The nitration reaction of 2-methylaniline gave
the 2-methyl-6-nitroacetanilide (2o) in 72% yield (Table 3, entry 8),
and 2-chloroaniline produced the ortho-nitro product in moderate
yield (Table 3, entry 9). While the nitration of 2-methoxy aniline
(Table 3, entry 10) mainly gave corresponding 4-nitro substituted
compound, 6-nitro isomer was not obtained. Since there are two
ortho-positions existed at the m-methyl or m-bromo anilines, the
yields of ortho-nitrated products (e.g., 2r, 2s) were lower (Table 3,
entries 11 and 12).
2
3
4
5
6
7
1i (R¼Me)
1j (R¼Cl)
2i
2j
2k
2l
2m
2n
98
96
91
86
74
Trace
1k (R¼Br)
1l (R¼OMe)
1m (R¼COMe)
1n (R¼NO2)
8d
9d
1o (R¼Me)
1p (R¼Cl)
2o
2p
72
48
4.6:1
1.2:1
10d
71
a:b 4:1
11d
12d
1r (R¼Me)
1s (R¼Br)
2r
2s
61
66
a:b:c 7.6:2.6:1
10.3:3:1
We further explored the reactions of multi-substituted anilines.
When phenyl ring bearing two chloro groups at ortho- and para-
positions, the product (2t) was obtained in 56% yield (Table 3, entry
13). The relatively low yield of this reaction might be due to the
electronic effect of two chloro groups, and part of amino group may
be oxidized into the nitro and isocyanate groups, which were
detected by GCeMS. When the 3- and 5-positions at aniline were
substituted with the strong electron-donating methoxy groups, the
yield of the ortho-nitrated product (2u) was decreased dramati-
cally, ascribed to the complicated reaction mixtures (Table 3, entry
13d
56
14d
15
38
30
14). Regrettably, nitration of
a-naphthylamine largely took place at
0.7:1
the para-position. The regioselectivity was dominated by steric
effect and only poor yield of ortho-nitrated product (2v) was ob-
tained (Table 2, entry 15). Besides the effect of directing group, the
nitration position of multi-substituted anilines is also influenced by
electron properties and steric hindrance of other groups.
a
To examine the practicality and synthetic potential of the one-
pot ortho-nitration using bismuth nitrate/acetic anhydride as mild
nitrating reagent, we finally carried out nitration of aniline and
hydrolytic reaction to produce o-nitroaniline (2aa) (Scheme 2). A
2 mmol scale reaction of aniline successfully afforded in 81% yield
of 2a under the optimal conditions and the target hydrolytic re-
action product 2aa was obtained in a 77% overall yield.
Reaction conditions: Primary anilines (0.2 mmol), Bi(NO3)3$5H2O (0.2 mmol),
Ac2O (1.2 mmol), and DCM (1.0 mL) were stirred at 23 ꢀC for 1e5 h under air.
b
Isolated yield.
c
o:p ratio determined by GC analysis of the crude reaction mixtures.
d
Ac2O (1.4 mmol).
On the basis of above results, the possible mechanism is
depicted in Scheme 3. Firstly, under the applied reaction condi-
tions, AcONO2 is generated in suit, next the reaction involves
electrophilic attack of its nitronium moiety at 1a,28 giving a charged
intermediate 1ab, which rearranges through a six-membered cyclic
Scheme 2. Synthesis of 2-nitroaniline.

Y. Lu et al. / Tetrahedron 69 (2013) 9422e9427
9425
transition state to form the arenium intermediate 1ac for ortho-
substitution. Finally, the arenium ion loses the Hþ to produce cor-
responding o-nitrated product 2a with a necessary base.
petroleum ether/EtOAc (4:1) as eluent to give the product (2a;
29 mg, 0.16 mmol) as a yellow solid in 81% yield.
4.2.1. N-(2-Nitrophenyl)acetamide (2a). Yellow solid (29 mg, 81%
yield), mp: 93e94 ꢀC. Column chromatography (petroleum ether/
EtOAc¼4:1, Rf¼0.48). The NMR data are consistent with those re-
ported in the literature.32 1H NMR (400 MHz, CDCl3):
d 10.33 (br s,
1H, NH), 8.77 (d, J¼8.4 Hz, 1H, AreH), 8.21 (d, J¼8.4 Hz, 1H, AreH),
7.65 (t, J¼7.8 Hz, 1H, AreH), 7.18 (t, J¼7.8 Hz, 1H, AreH), 2.30 (s, 3H,
COCH3); 13C NMR (100 MHz, CDCl3):
d 169.1, 136.4, 136.0, 134.9,
125.8, 123.3, 122.2, 25.7; GCeMS (EI, m/z): 180 [M]þ.
4.2.2. N-(2-Nitrophenyl)isobutyramide (2b). Yellow solid (35 mg,
84% yield), mp: 72e73 ꢀC. Column chromatography (petroleum
ether/EtOAc¼5:1, Rf¼0.60). The NMR data are consistent with those
reported in the literature.33 1H NMR (400 MHz, CDCl3):
d 10.48 (br s,
Scheme 3. Possible mechanism for regioselective ortho-nitration of acetanilide.
1H, NH), 8.82 (d, J¼8.4 Hz, 1H, AreH), 8.23 (d, J¼8.4 Hz, 1H, AreH),
7.65 (t, J¼7.8 Hz, 1H, AreH), 7.18 (t, J¼7.8 Hz, 1H, AreH), 2.67
(heptet, J¼6.7 Hz, 1H, CH), 1.32 (d, J¼6.8 Hz, 6H, CH3). 13C NMR
3. Conclusion
(100 MHz, CDCl3):
d 176.3, 136.4, 136.2, 135.4, 125.9, 123.2, 122.3,
37.8, 19.6; GCeMS (EI, m/z): 208 [M]þ.
In summary, we have developed an efficient method for the
regioselective ortho-nitration of N-phenyl carboxamides and pri-
mary anilines using the commercially available, inexpensive bis-
muth nitrate and acetic anhydride as the nitrating reagents.
Furthermore, a wide range of primary anilines can be applied in
a one-pot reaction to afford the desired o-nitroacetanilides in good
to excellent yields. The mild reaction conditions provide a potential
ortho-nitration methodology in both academic and industry.
4.2.3. 2,2,2-Trifluoro-N-(2-nitrophenyl)acetamide (2c). White solid
(20 mg, 43% yield), mp: 88e89 ꢀC. Column chromatography (pe-
troleum ether/EtOAc¼5:1, Rf¼0.63). The NMR data are consistent
with those reported in the literature.29 1H NMR (400 MHz, CDCl3):
d
11.41 (br s, 1H, NH), 8.75 (d, J¼8.6 Hz, 1H, AreH), 8.33 (d,
J¼8.6 Hz, 1H, AreH), 7.78 (t, J¼8.0 Hz, 1H, AreH), 7.38 (t, 8.0 Hz,
1H, AreH); 13C NMR (100 MHz, CDCl3):
d
155.4 (q, J¼39 Hz), 137.1,
136.6, 132.3, 126.4, 125.8, 122.4, 115.5 (q, J¼287 Hz); GCeMS (EI, m/
z): 234 [M]þ.
4. Experimental section
4.1. General information
4.2.4. N-(2-Nitrophenyl)benzanilide (2d). Yellow solid (39 mg, 81%
yield), mp: 93e94 ꢀC. Column chromatography (petroleum ether:
EtOAc¼10:1, Rf¼0.42). The NMR data are consistent with those
All reagents unless otherwise noted were obtained from com-
mercial sources and used without further purification. All these
reactions were monitored by TLC with silica gel GF254 precoated
plates and the products were isolated by column chromatography
on silica gel (300e400 mesh size) by using petroleum ether
(60e90 ꢀC) and ethyl acetate as eluents. All compounds were
characterized by 1H NMR, 13C NMR, and Mass spectroscopy. 1H NMR
and 13C NMR spectra were recorded on INOVA 400 instrument with
operating frequency of 400 and 100 MHz, respectively. Chemical
shifts for 1H NMR were reported in ppm relative to TMS. The fol-
lowing abbreviations are used to set multiplicities: s¼singlet,
d¼doublet, t¼triplet, dd¼doublet of doublets, br¼broad. Coupling
constants (J) were reported in Hertz (Hz). Gas chromatography
analyses were performed with an FID detector. GCeMS data were
also performed. Starting materials N-phenyl carboxamides 1b, 1d,
1e, 1f,29 1c,30 and 1g31 were prepared according to the reported
procedures.
reported in the literature.34 1H NMR (400 MHz, CDCl3):
d 11.37 (br s,
1H, NH), 9.02 (d, J¼8.4 Hz, 1H, AreH), 8.29 (d, J¼8.4 Hz, 1H, AreH),
8.00 (d, J¼7.2 Hz, 2H, AreH), 7.72 (t, J¼7.4 Hz, 1H, AreH), 7.62 (t,
J¼7.2 Hz, 1H, AreH), 7.55 (t, J¼7.2 Hz, 2H, AreH), 7.23 (t, J¼7.4 Hz,
1H, AreH); 13C NMR (100 MHz, CDCl3):
d 165.9, 136.6, 136.4, 135.5,
134.2, 132.8, 129.2, 127.6, 126.1, 123.5, 122.3; GCeMS (EI, m/z): 242
[M]þ.
4.2.5. 4-Chloro-N-(2-nitrophenyl)benzamide (2e). Yellow solid
(50 mg, 91% yield), mp: 146e147 ꢀC. Column chromatography
(petroleum ether/EtOAc¼5:1, Rf¼0.62). The NMR data are consis-
tent with those reported in the literature.35 1H NMR (400 MHz,
CDCl3):
d
11.34 (br s, 1H, NH),
d
8.97 (d, J¼8.6 Hz, 1H, AreH), 8.28 (d,
J¼8.6 Hz, 1H, AreH), 7.93 (d, J¼8.2 Hz, 2H, AreH), 7.72 (t, J¼8.4 Hz,
1H, AreH), 7.52 (d, J¼8.2 Hz, 2H, AreH), 7.23 (t, J¼8.4 Hz, 1H,
AreH); 13C NMR (100 MHz, CDCl3):
d 164.8, 139.3, 136.5, 135.3,
132.6, 132.4, 129.5, 128.9, 126.1, 123.7, 122.2; GCeMS (EI, m/z): 276
[M]þ.
4.2. Representative procedure for the regioselective ortho-
nitration of N-phenyl carboxamides and primary anilines
4.2.6. N-Methyl-N-(2-nitrophenyl)acetamide (2f) and N-methyl-N-
(4-nitrophenyl)acetamide (2f0). Yellow oil (36 mg, 93% yield). Col-
umn chromatography (petroleum ether/EtOAc¼1:2, Rf¼0.43). N-
Methyl-N-(4-nitrophenyl)acetamide (2f0) exists in cis and trans
conformers.36 Approx. 1.6:1 mixture of cis and trans conformers. 1H
A flame-dried reaction vessel with a magnetic stirring bar was
charged with acetanilide (1a; 27 mg, 0.2 mmol), Bi(NO3)3$5H2O
(97 mg, 0.2 mmol), dichloromethane (1 mL), and Ac2O (114
mL,
1.2 mmol) in sequence. The mixture was stirred at room tempera-
ture under air for 3 h. The reaction mixture was cooled to ambient
temperature and poured into a saturated solution of NaHCO3. The
resulting mixture was extracted with ethyl acetate (3ꢁ20 mL). The
combined organic layer was dried with Na2SO4 and then concen-
trated under vacuum. After evaporation, the residue was purified
by column chromatography on silica gel (300e400 mesh size) using
NMR (400 MHz, CDCl3): Major component (2f):
d
8.30 (d, J¼8.8 Hz,
1H, AreH), 8.02 (d, J¼8.8 Hz, 1H, AreH), 7.74 (t, J¼7.8 Hz, 1H, AreH),
7.59 (t, J¼7.8 Hz,1H, AreH), 3.22 (s, 3H, NeCH3),1.83 (s, 3H, COCH3);
Minor component (2f0):
AreH), 7.46 (d, J¼7.6 Hz, AreH), 7.42 (d, J¼6.8 Hz, AreH), 7.34 (d,
J¼7.6 Hz, AreH), 3.45 (s, NeCH3, trans conformer), 3.36 (s, NeCH3,
cis conformer), 2.26 (s, COCH3, trans conformer), 2.04 (s, COCH3, cis
d
7.98 (d, J¼8.0 Hz, AreH), 7.70e7.63 (m,

9426
Y. Lu et al. / Tetrahedron 69 (2013) 9422e9427
conformer), 13C NMR (100 MHz, CDCl3):
d
170.0, 150.0, 146.8, 137.6,
138.5, 136.3, 129.8, 126.5, 122.9, 23.9, 19.2; GCeMS (EI, m/z): 194
[M]þ.
134.6, 134.3, 131.0, 129.6, 129.3, 128.1, 127.4, 125.7, 125.2, 125.1, 39.4,
36.8, 22.8, 22.2; GCeMS (EI, m/z): 194 [M]þ.
4.2.14. N-(2-Chloro-6-nitrophenyl)acetanilide (2p). White solid
(21 mg, 48% yield), mp: 190e191 ꢀC (lit44 190e191 ꢀC). The crude
product was purified by preparative HPLC on a C18 reversed-phase
4.2.7. N-(2-Nitrophenyl)maleimide (2g). White solid (18 mg, 40%
yield), mp: 130e131 ꢀC. Column chromatography (petroleum ether/
EtOAc¼2:1, Rf¼0.44). The NMR data are consistent with those re-
column (5
mm, 10*250 mm) using 65% (v/v) aqueous methanol
ported in the literature.37 1H NMR (400 MHz, CDCl3):
d 8.17 (d,
solution as eluent with the use of a UV detector at 254 nm. 1H NMR
J¼8.0 Hz, 1H, AreH), 7.77 (t, J¼8.0 Hz, 1H, AreH), 7.62 (t, J¼8.0 Hz,
(400 MHz, DMSO-d6):
d
10.27 (br s, 1H, NH), 7.91 (d, J¼8.0 Hz, 2H,
1H, AreH), 7.44 (d, J¼8.0 Hz, 1H, AreH), 6.94 (s, 2H, CH); 13C NMR
AreH), 7.50 (t, J¼8.0 Hz, 1H, AreH), 2.07 (s, 3H, COCH3); 13C NMR
(100 MHz, CDCl3):
d
168.6, 145.5, 135.1, 134.4, 131.0, 129.9, 126.0,
(100 MHz, DMSO-d6): d 168.6, 147.2, 134.1, 131.4, 128.2, 127.6, 123.6,
125.2; GCeMS (EI, m/z): 218 [M]þ.
22.6; GCeMS (EI, m/z): 214 [M]þ.
4.2.8. N-(4-Methyl-2-nitrophenyl)acetamide
(2i). Yellow
solid
4.2.15. N-(2-Methoxy-4-nitrophenyl)acetamide (2q). Yellow solid
(30 mg, 71% yield); mp: 136e138 ꢀC (lit45 139.5e140.5 ꢀC). Column
chromatography (petroleum ether/EtOAc¼1:1, Rf¼0.40). 1H NMR
(38 mg, 98% yield), mp: 95e96 ꢀC. Column chromatography (pe-
troleum ether/EtOAc¼4:1, Rf¼0.45). The NMR data are consistent
with those reported in the literature.38 1H NMR (400 MHz, CDCl3):
(400 MHz, CDCl3):
d
8.57 (d, J¼9.0 Hz,1H, AreH), 8.02 (br s,1H, NH),
d
10.22 (br s, 1H, NH), 8.63 (d, J¼8.6 Hz, 1H, AreH), 8.01 (s, 1H,
AreH), 7.46 (d, J¼8.6 Hz, 1H, AreH), 2.39 (s, 3H, CH3), 2.28 (s, 3H,
COCH3); 13C NMR (100 MHz, CDCl3):
169.1, 137.1, 136.4, 133.6,
132.6, 125.7, 122.3, 25.7, 20.7; GCeMS (EI, m/z): 194 [M]þ.
7.90 (dd, J¼9.0, 2.4 Hz, 1H, AreH), 7.74 (d, J¼2.4 Hz, 1H, AreH), 4.00
(s, 3H, OMe), 2.27 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3):
d
d 168.8, 147.3, 143.1, 134.0, 118.4, 117.9, 105.3, 56.5, 25.2; GCeMS (EI,
m/z): 210 [M]þ.
4.2.9. N-(4-Chloro-2-nitrophenyl)acetanilide
(2j). Yellow solid
4.2.16. N-(5-Methyl-2-nitrophenyl)acetamide (2r). Yellow solid
(24 mg, 61% yield), mp: 84e85 ꢀC. Column chromatography (pe-
troleum ether/EtOAc¼4:1, Rf¼0.55). 1H NMR (400 MHz, CDCl3):
(41 mg, 96% yield), mp: 99e100 ꢀC. Column chromatography (pe-
troleum ether/EtOAc¼4:1, Rf¼0.4). The NMR data are consistent
with those reported in the literature.39 1H NMR (400 MHz, CDCl3):
d
10.42 (br s, 1H, NH), 8.60 (s, 1H, AreH), 8.11 (d, J¼8.4 Hz, 1H,
d
10.26 (br s, 1H, NH), 8.78 (d, J¼9.2 Hz, 1H, AreH), 8.20 (s, 1H,
AreH), 6.97 (d, J¼8.4 Hz, 1H, AreH), 2.44 (s, 3H, CH3), 2.29 (s, 3H,
AreH), 7.61 (d, J¼9.2 Hz, 1H, AreH), 2.31 (s, 3H, COCH3); 13C NMR
COCH3); 13C NMR (100 MHz, CDCl3):
d 169.2, 148.2, 135.0, 134.3,
(100 MHz, CDCl3):
d
169.1, 136.5, 136.1, 133.7, 128.5, 125.4, 123.5,
125.9, 124.3, 122.2, 25.8, 22.3; GCeMS (EI, m/z): 194 [M]þ.
25.77; GCeMS (EI, m/z): 214 [M]þ.
4.2.17. N-(5-Bromo-2-nitrophenyl)acetamide (2s). Yellow solid
(34 mg, 66% yield), mp: 142e143 ꢀC (lit44 140 ꢀC). Column chro-
matography (petroleum ether/EtOAc¼4:1, Rf¼0.52). 1H NMR
4.2.10. N-(4-Bromo-2-nitrophenyl)acetamide (2k). Yellow solid
(47 mg, 91% yield), mp: 106e107 ꢀC. Column chromatography
(petroleum ether/EtOAc¼4:1, Rf¼0.33). The NMR data are consis-
tent with those reported in the literature.40 1H NMR (400 MHz,
(400 MHz, CDCl3):
d
10.41 (br s,1H, NH), 9.06 (d, J¼2.0 Hz,1H, AreH),
8.09 (d, J¼9.0 Hz, 1H, AreH), 7.31 (dd, J¼9.0, 2.0 Hz, 1H, AreH), 2.31
CDCl3):
d
10.27 (br s, 1H, NH), 8.72 (d, J¼9.2 Hz, 1H, AreH), 8.35 (s,
(s, 3H, COCH3); 13C NMR (100 MHz, CDCl3):
d 169.2, 135.8, 134.9,
1H, AreH), 7.74 (d, J¼9.2 Hz, 1H, AreH), 2.30 (s, 3H, COCH3); 13C
131.7, 127.0, 126.6, 124.8, 25.8; GCeMS (EI, m/z): 258 [M]þ.
NMR (100 MHz, CDCl3):
d 169.1, 138.9, 136.6, 134.1, 128.3, 123.7,
115.4, 25.8; GCeMS (EI, m/z): 258 [M]þ.
4.2.18. N-(2,4-Dichloro-6-nitrophenyl)acetamide (2t). White solid
(28 mg, 56% yield), mp: 180e181 ꢀC. Column chromatography
(petroleum ether/EtOAc¼4:1, Rf¼0.63). The NMR data are consis-
tent with those reported in the literature.46 1H NMR (400 MHz,
4.2.11. N-(4-Methoxy-2-nitrophenyl)acetamide (2l). Yellow solid
(36 mg, 86% yield), mp: 115e116 ꢀC. Column chromatography
(petroleum ether/EtOAc¼2:1, Rf¼0.37). The NMR data are consis-
tent with those reported in the literature.41 1H NMR (400 MHz,
CDCl3):
d
7.86 (d, J¼1.6 Hz, 1H, AreH), 7.73 (br s, 1H, NH), 7.70 (d,
J¼1.6 Hz, AreH), 2.24 (s, 1H, COCH3); 13C NMR (100 MHz, CDCl3):
CDCl3):
J¼3.0 Hz, 1H, AreH), 7.23 (dd, J¼9.2, 3.0 Hz, 1H, AreH), 3.86 (s, 3H,
OCH3), 2.27 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3):
168.9,
d
10.05 (br s, 1H, NH), 8.63 (d, J¼9.2 Hz, 1H, AreH), 7.66 (d,
d 168.2, 146.0, 134.1, 132.7, 132.2, 127.2, 124.2, 23.7; GCeMS (EI, m/
z): 248 [M]þ.
d
155.1, 137.2, 128.6, 124.0, 123.6, 108.6, 56.1, 25.6; GCeMS (EI, m/z):
4.2.19. N-(3,5-Dimethoxy-2-nitrophenyl)acetamide
(2u). Yellow
210 [M]þ.
solid (18 mg, 38% yield), mp: 148e149 ꢀC. Column chromatography
(petroleum ether/EtOAc¼2:1, Rf¼0.37). 1H NMR (400 MHz, CDCl3):
4.2.12. N-(4-Acetyl-2-nitrophenyl)acetamide (2m). Yellow solid
(33 mg, 74% yield), mp: 144e145 ꢀC (lit42 140e141 ꢀC). Column
chromatography (petroleum ether/EtOAc¼1:1, Rf¼0.59). 1H NMR
d
9.19 (br s, 1H, NH), 7.69 (d, J¼2.2 Hz, 1H, AreH), 6.28 (d, J¼2.2 Hz,
1H, Ar-H), 3.89 (s, 3H, OCH3), 3.87 (s, 3H, OCH), 2.22 (s, 3H, COCH3);
13C NMR (100 MHz, CDCl3):
d 169.0, 163.7, 155.6, 135.4 (over-
(400 MHz, CDCl3):
d
10.57 (br s, 1H, NH), 8.94 (d, J¼8.9 Hz, 1H,
lapping), 97.8, 95.8, 56.8, 56.1, 25.9; GCeMS (EI, m/z): 240 [M]þ.
AreH), 8.81 (d, J¼1.9 Hz, 1H, AreH), 8.22 (dd, J¼8.9, 1.9 Hz, 1H,
AreH), 2.65 (s, 3H, p-COCH3), 2.35 (s, 3H, COCH3); 13C NMR
4.2.20. N-(2-Nitronaphthalen-1-yl)acetamide (2v). Yellow solid
(14 mg, 30% yield), mp: 204e205 ꢀC (lit47 202e203 ꢀC). Column
chromatography (petroleum ether: EtOAc¼1:1, Rf¼0.46). 1H NMR
(100 MHz, CDCl3):
d 194.9, 169.3, 138.5, 135.7, 135.3, 131.8, 126.4,
122.0, 26.6, 26.0; GCeMS (EI, m/z): 222 [M]þ.
(400 MHz, DMSO-d6):
d 10.54 (br s, 1H, NH), 8.31e8.20 (m, 1H,
4.2.13. N-(2-Methyl-6-nitrophenyl)acetamide (2o). White solid
(28 mg, 72% yield), mp: 154e155 ꢀC. Column chromatography
(petroleum ether/EtOAc¼4:1, Rf¼0.38). The NMR data are consis-
tent with those reported in the literature.43 1H NMR (400 MHz,
AreH), 8.17e8.07 (m, 1H, AreH), 8.04 (d, J¼8.8 Hz, 1H, AreH), 7.95
(d, J¼8.8 Hz, 1H, AreH), 7.81e7.72 (m, 2H, AreH), 2.18 (s, 3H); 13C
NMR (100 MHz, DMSO-d6): d 169.0, 142.7, 134.8, 129.1, 128.8, 128.3,
127.9, 127.6, 127.1, 124.8, 120.5, 22.9; GCeMS (EI, m/z): 230 [M]þ.
CDCl3):
J¼8.0 Hz, 1H, AreH), 7.27 (t, J¼8.0 Hz, 1H, AreH), 2.32 (s, 3H,
COCH3), 2.22 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3):
168.5, 145.1,
d
8.35 (br s, 1H, NH), 7.82 (d, J¼8.0 Hz, 1H, AreH), 7.51 (d,
4.2.21. o-Nitroaniline (2aa). Yellow solid (213 mg, 77% yield), mp:
69e70 ꢀC. Column chromatography (petroleum ether/EtOAc¼4:1,
d

Y. Lu et al. / Tetrahedron 69 (2013) 9422e9427
9427
Rf¼0.47). 1H NMR (400 MHz, CDCl3):
8.09 (d, J¼8.6 Hz, 1H, AreH),
d
14. Suzuki, H.; Ishibashi, T.; Murashima, T.; Tsukamoto, K. Tetrahedron Lett. 1991, 32,
6591.
15. Sridhar Rao, A.; Srinivas, P.; Suresh Babu, K.; Madhusudana Rao, J. Tetrahedron
7.35 (t, J¼7.7 Hz, 1H, AreH), 6.82 (d, J¼8.6 Hz, 1H, AreH), 6.69 (t,
J¼7.7 Hz, 1H, AreH), 6.12 (br s, 2H, NH2); 13C NMR (100 MHz,
Lett. 2005, 46, 8141.
16. (a) Naveen, T.; Maity, S.; Sharma, U.; Maiti, D. J. Org. Chem. 2013, 78, 5949; (b)
Taniguchi, T.; Ishibashi, H. Org. Lett. 2010, 12, 124; (c) Taniguchi, T.; Fujii, T.;
Ishibashi, H. Org. Biomol. Chem. 2011, 9, 653; (d) Taniguchi, T.; Fujii, T.; Ishibashi,
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CDCl3):
d 144.9, 135.8, 132.2, 126.1, 118.9, 116.9; GCeMS (EI, m/z):
138 [M]þ.
Acknowledgements
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This work was supported by the National Natural Science
Foundation of China (Project No. 21176039, 20876021, and
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Supplementary data
Supplementary data (experimental procedures and copies of
NMR spectra) associated with this article can be found in the online
version, at http://dx.doi.org/10.1016/j.tet.2013.08.076. These data
include MOL files and InChiKeys of the most important compounds
described in this article.
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