Rhodium-catalyzed direct C-H amidation of azobenzenes with sulfonyl azides: A synthetic route to sterically hindered ortho-substituted aromatic azo compounds

Article abstract of DOI:10.1021/jo500372d

A rhodium(III)-catalyzed direct ortho-amidation of azobenzenes with sulfonyl azides as the amino source is disclosed. This reaction exhibits a broad substrate scope, high functional group tolerance, and regioselectivity, providing a variety of sterically hindered ortho-substituted azobenzene derivatives in good to excellent yield.

Full text of DOI:10.1021/jo500372d

Note
pubs.acs.org/joc
Rhodium-Catalyzed Direct C−H Amidation of Azobenzenes with
Sulfonyl Azides: A Synthetic Route to Sterically Hindered ortho-
Substituted Aromatic Azo Compounds
Xuefeng Jia* and Jie Han
School of Chemical and Material Science, Shanxi Normal University, Linfen, 041004, China
S
* Supporting Information
ABSTRACT: A rhodium(III)-catalyzed direct ortho-amida-
tion of azobenzenes with sulfonyl azides as the amino source is
disclosed. This reaction exhibits a broad substrate scope, high
functional group tolerance, and regioselectivity, providing a
variety of sterically hindered ortho-substituted azobenzene
derivatives in good to excellent yield.
Scheme 1. Transition-Metal-Catalyzed Direct C−H
t is well-known that aromatic azo compounds are important
materials and have been broadly applied in many fields due
Amidation with Azides
I
to their unique properties. They can be used as light-triggered
switches in surface-modified materials,1 polymers,2 molecular
machines,3 protein probes,4 organic dyes,5 nonlinear optical
devices,6 chemosensors,7 and so forth. Recently, significant
attention has been focused on direct C−H functionalization of
azobenzenes using the azo group as a directing group. Wang et
al. and Zeng et al. reported palladium-catalyzed ortho-acylation
of azobenzenes with α-oxocarboxylic acids,8 aldehydes,9 and
aryl methanes.10 The palladium-catalyzed ortho-alkoxylation
and halogenation of aromatic azo compounds were reported by
Sun et al.11 and Ma and Tian,12 respectively. A rhodium(III)-
catalyzed C−H bond addition of azobenzenes to aldehydes was
also developed.13 Despite the achievements that have been
made with respect to direct C−H functionalization of
azobenzenes, the formation of a C−N bond is rarely studied
in the C−H activation process. To the best of our knowledge,
the direct C−H amidation of azobenzenes with sulfonyl azides
has never been reported. Very recently, transition-metal-
catalyzed direct C−H amidation using sulfonyl azides as the
amino source has attracted a great deal of attention.14 Herein,
we report a highly efficient strategy for the synthesis of
sterically hindered aromatic azo compounds through Rh(III)-
catalyzed ortho-amidation of azobenzenes with sulfonyl azides
via azo-directed C−H activation (Scheme 1).
reaction activity of azobenzene (1a) with p-toluenesulfonyl
azide (2a) could be enhanced by the use of AgNTf2 as additive,
leading to the formation of 3a in 63% yield (entry 4). Screening
of a range of solvents revealed that DCE was found to be the
best solvent of choice compared with THF, toluene, and
DMSO (entries 5−7). The critical improvement of reactivity
was achieved by the use of a slight excess of azobenzene (1a).
The amidation reaction proceeded smoothly at 90 °C in DCE
to give the desired product 3a in 75% yield when the ratio of
1a/2a was switched to 1.5:1 (entry 8). There was no obvious
promotion with an increase in the ratio of 1a/2a to 2:1 (entry
9). Some additives, such as AgBF4, AgNO3, and Ag2O, were
also tested. In the presence of AgBF4, the yield of product 3a
had a slight decrease (entry 10), but the presence of AgNO3
and Ag2O was obviously not favorable for this reaction (entries
We started to optimize the reaction conditions by using
azobenzene (1a) and p-toluenesulfonyl azide (2a) as the
substrate (Table 1). The activities of different metal catalysts in
combination with AgSbF6 were first examined in 1,2-dichloro-
ethane (DCE) at 80 °C for 36 h. Unfortunately, the use of
[Ru(p-cymene)Cl2]2 and [Cp*IrCl2]2 proved unsuccessful in
catalyzing this amidation reaction (entries 1 and 2). However, a
trace amount of desired product 3a was isolated when
[Cp*RhCl2]2 was employed (entry 3). Gratifyingly, the
Received: February 15, 2014
Published: March 31, 2014
© 2014 American Chemical Society
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Note
a
Table 1. Optimization of Reaction Conditions
d
entry
catalyst
additive
solvent
T (°C)
yield (%)
e
1
2
3
4
5
6
7
[Ru(p-cymene)Cl2]2
[Cp*IrCl2]2
AgSbF6
AgSbF6
AgSbF6
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgBF4
DCE
DCE
DCE
DCE
THF
Toulene
DMSO
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
80
80
n. d.
e
n. d.
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
80
<10
63
80
80
19
e
110
110
90
n. d.
e
n. d.
b
h
8
75(72)
c
f
9
90
78(63)
b
10
90
50
b
e
11
AgNO3
Ag2O
90
n. d.
b
e
12
b
90
n. d.
13
AgNTf2
AgNTf2
AgNTf2
AgNTf2
100
120
90
68
63
b
14
g
15
16
68
g
90
78
a
Reaction conditions: 1a (0.15 mmol), 2a (2.0 equiv), catalyst (5 mol %), additive (20 mol %) in solvent (1.0 mL) at the indicated temperature for
b
c
36 h. Reaction conditions: 1a (1.5 equiv), 2a (0.1 mmol), [Cp*RhCl2]2 (5 mol %), additive (20 mol %) in DCE at 90 °C for 36 h. The reaction
was carried out with 1a (2.0 equiv) and 2a (0.1 mmol). Isolated yield. The formation of product was not detected. 1a (0.15 mmol) and 2a (1.0
equiv) were used as substrate. [Cp*RhCl2]2 (2.5 and 10 mol %) was used. The reaction was carried out on a 10 mmol scale.
d
e
f
g
h
11 and 12). Different reaction temperatures were further
investigated. Raising the temperature diminished the yield of
the product 3a (entries 13 and 14). Finally, the lower yield of
3a was obtained when 2.5 mol % [Cp*RhCl2]2 was used (entry
15), while utilizing [Cp*RhCl2]2 (10 mol %) as the catalyst did
not show higher catalytic activity (entry 16). After screening
several parameters, eventually, the following conditions were
chosen for examination of the reaction scope: [Cp*RhCl2]2 (5
mol %), AgNTf2 (20 mol %), and 1a/2a = 1.5:1 in DCE at 90
°C for 36 h.
Table 2. Rh-Catalyzed ortho-Amidation of Azobenzene with
Different Sulfonyl Azides
a b
,
With the optimized conditions for the amidation of
azobenzene in hand, we next examined the scope of this
methodology. As summarized in Table 2, the C−H amidation
of azobenzene (1a) with various sulfonyl azides could proceed
smoothly and furnish the corresponding ortho-substituted
products. The substituent on the benzene ring of sulfonyl
azides showed obvious electronic effects on reaction activity.
The substrates with a para-electron-withdrawing group (such as
4-F, 4-Cl, 4-Br) afforded the products 3b−3d in good yields
(80−86%), while the substrates with a strong meta-electron-
withdrawing group (−NO2) provided the corresponding
product 3e in 76% yield. Interestingly, the reaction of
azobenzene (1a) with p-trifluoromethylphenylsulfonyl azide
led to the desired azo compound 3f in 90% yield. When the
substrates with a para-electron-donating group (4-t-Bu, 4-
OMe) were used, the ortho-substituted azobenzene derivatives
3h and 3i were obtained with 93% and 92% yields, respectively.
To our delight, this catalytic system could be further extended
to other sulfonyl azides. The 2-naphthyl sulfonyl azide could
give the product 3j in 89% yield under the same conditions.
The 2-thienyl- and n-butyl-substituted sulfonyl azides could
react well with azobenzene to facilitate the desired products 3k
and 3l in excellent yields (94% and 96%, respectively).
a
Reaction conditions: 1a (1.5 equiv), 2 (0.1 mmol), [Cp*RhCl2]2 (5
mol %), AgNTf2 (20 mol %) in 1,2-dichloroethane (1 mL) at 90 °C
b
for 36 h. Isolated yield.
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Note
1
After screening of different sulfonyl azides, the scope of
substituted azobenzenes was then explored with p-toluenesul-
fonyl azide (2a). As can be seen from Table 3, the catalytic
the primary regioisomers, which could be determined by H
NMR, were obtained in lower yields (45% for 4h; 40% for 4i;
50% for 4j, respectively). Finally, azobenzene with a nitro group
at the meta position reacted with p-toluenesulfonyl azide (2a)
to give the corresponding product 4k in 35% yield, which
further showed that a substrate with an electron-withdrawing
group on the phenyl ring of azobenzene was unfavorable to the
reaction.
Table 3. Rh-Catalyzed ortho-Amidation of Substituted
a b c d
, , ,
Azobenzenes with p-Toluenesulfonyl Azide
On the basis of our experimental results and the previous
literature,14 a plausible mechanism for this direct amidation
reaction is proposed in Scheme 2. First, this transformation
Scheme 2. Plausible Reaction Mechanism
a
Reaction conditions: 1 (1.5 equiv), 2a (0.1 mmol), [Cp*RhCl2]2 (5
mol %), AgNTf2 (20 mol %) in 1,2-dichloroethane (1 mL) at 90 °C
b
c
for 36 h. Isolated yield. The reaction was carried out by using 1 (1.5
d
equiv) and 2a (10 mmol). The meta-methyl substituted azobenene
and p-methoxysulfonyl azide were used as substrate.
system proved to be broadly applicable and was found to be
tolerant of electron-withdrawing (F, Cl, OCF3) or electron-
donating (4-OMe, 4-Me, 3-Me) functional groups. Substituents
on the aromatic moiety of the aromatic azo compounds
influenced the efficiency of this amidation reaction significantly.
Substrates with a halogen atom (Cl or F) at the para position of
the phenyl ring proceeded smoothly to give the corresponding
products 4a and 4b in moderate yields (55% and 60%,
respectively). The direct amidation of aromatic azo compounds
bearing a strong electron-withdrawing group (OCF3) was less
efficient compared to those derivatives having a weak electron-
withdrawing group at the para position of the phenyl ring. To
our surprise, substrates bearing an electron-donating group,
such as methyl or methoxy, at the para position of the phenyl
ring furnished the desired product in moderate to good yield
(65% for 4d; 70% for 4e). It should be noted that the yield of
product had a sharp increase when azobenzene derivatives with
a methyl group at the meta position of the phenyl ring was used
as the substrate. The reaction of meta-methyl-substituted
azobenzene with para-methoxysulfonyl azide led to the product
4g in almost quantitative yield (98%) probably due to the
“electron-donating” effect from methyl and methoxy groups.
We also investigated the electronic effect of substituents on the
regioselectivity of the ortho-amidation of unsymmetric azoar-
enes and found that these amidation reactions mainly took
place on the electron-rich azo aromatic rings, and a trace
amount of another regioisomer was observed by TLC. When
unsymmetrical azobenzenes were employed as the substrates,
may begin with formation of the cyclorhodium intermediate A
through the reaction of azobenzene (1a) with the [Cp*RhIII-
(NTf2)2]+ species generated from [Cp*RhCl2]2 and AgNTf2,
which was treated with sulfonyl azide (2a) to provide
intermediate B. Subsequent concerted migratory insertion led
to the formation of a rhodium(III) amido species C. Finally, the
desired product (3a) was obtained and the [Cp*RhIII(NTf2)2]+
species was regenerated to complete the catalytic cycle by
protonolysis of intermediate C.
In summary, a rhodium(III)-catalyzed direct ortho-amidation
of aromatic azo compounds via C−H bond activation with
sulfonyl azides as the amino source has been developed. This
protocol provided a convenient method for synthesis of
sterically hindered ortho-substituted symmetrical and unsym-
metrical azobenzene derivatives, which could tolerate a wide
range of functional groups, such as chloro, bromo, nitro,
methyl, and methoxy groups, on the phenyl ring. The method
was also applicable to heteroaromatic and aliphatic sulfonyl
azides.
EXPERIMENTAL SECTION
■
General Methods. Unless otherwise stated, all manipulations were
performed in a sealed tube with a Teflon-lined cap under an air
atmosphere. Chemicals were commercially available and used without
purification. Sulfonyl azide substrates14e and aromatic azo com-
pounds15 were prepared according to the literature procedure. 1H
NMR and 13C NMR spectra were recorded on a 400 or 300
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The Journal of Organic Chemistry
Note
spectrometer, and chemical shifts are reported in parts per million
2-(4-Trifluoromethylphenylsulfonamido)azobenzene (3f). Yield
90% (36.5 mg); pale yellow solid, mp 107−108 °C; H NMR (400
1
1
(ppm) using (CH3)4Si (for H, δ = 0.00; for 13C, δ = 77.00) as the
MHz, CDCl3): δ 9.71 (s, 1H), 7.88 (d, J = 8.0 Hz, 2H), 7.80−7.76 (m,
3H), 7.73 (dd, J = 1.2, 8.4 Hz, 1H), 7.57 (d, J = 8.0 Hz, 2H), 7.55 (dd,
J = 1.6, 4.8 Hz, 3H), 7.43 (dt, J = 1.6, 8.4 Hz, 1H), 7.23 (t, J = 8.4 Hz,
1H); 13C NMR (100 MHz, CDCl3): δ 151.8, 140.4, 134.5, 133.5,
132.6, 132.0, 129.4, 127.6, 126.2, 126.1, 125.1, 124.4, 123.3, 122.8,
120.7. HRMS (ESI) m/z: Calcd for C19H14F3N3O2S: [M + H]+
406.0832, found 406.0835. IR (KBr, cm−1): 3265, 2920, 1584, 1328,
1174, 1065, 925, 718, 688, 532.
internal standard. The following abbreviations are used to denote the
multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet. Coupling constants (J) were reported in hertz unit (Hz).
Melting points are uncorrected. C, H, and N analyses were measured
on an elemental analyzer. HRMS data were obtained by ESI on a TOF
mass analyzer. IR spectra were recorded as KBr pellets on an FTIR-
8500 spectrometer.
General Procedure for Rhodium(III)-Catalyzed Direct ortho-
Amidation of Azobenzenes with Sulfonyl Azides. To a 25 mL
sealed tube with a Teflon-lined cap were added azobenzene 1 (1.5
equiv), sulfonyl azide 2 (0.1 mmol), [Cp*RhCl2]2 (3.1 mg, 5 mol %),
AgNTf2 (7.76 mg, 20 mol %), and 1,2-dichloroethane (1 mL) under
atmospheric conditions. The reaction mixture was stirred in a
preheated oil bath at 90 °C for 36 h. After the mixture was cooled
to room temperature, the volatiles were removed under reduced
pressure, and the residue was purified by preparative thin layer
chromatography on silica gel using petroleum ether/ethyl acetate (5:1)
as the eluent to give the desired product 3 or 4.
2-(4-Methylphenylsulfonamido)azobenzene (3a). Yield 75% (26.3
mg); pale yellow solid, mp 129−130 °C; 1H NMR (400 MHz,
CDCl3): δ 9.75 (s, 1H), 7.82−7.80 (m, 2H), 7.75−7.70 (m, 2H), 7.67
(d, J = 8.4 Hz, 2H), 7.54−7.51 (m, 3H), 7.39 (t, J = 8.4 Hz, 1H), 7.17
(d, J = 8.0 Hz, 1H), 7.12 (d, J = 8.4 Hz, 2H), 2.28 (s, 3H); 13C NMR
(100 MHz, CDCl3): δ 151.9, 144.0, 140.0, 136.2, 134.5, 132.5, 131.7,
129.7, 129.3, 127.2, 124.3, 122.8, 122.7, 120.2, 21.5. Anal. Calcd for
C19H17N3O2S: C, 64.94; H, 4.88; N, 11.96. Found: C, 64.85; H, 4.91;
N, 12.02. IR (KBr, cm−1): 3253, 3055, 2915, 1580, 1453, 1300, 1150,
1072, 925, 775, 691, 525.
2-(4-Fluorophenylsulfonamido)azobenzene (3b). Yield 80% (28.4
mg); pale yellow solid, mp 117−118 °C; 1H NMR (400 MHz,
CDCl3): δ 9.75 (s, 1H), 7.83−7.75 (m, 5H), 7.71 (dd, J = 1.2, 8.4 Hz,
1H), 7.55−7.53 (m, 3H), 7.42 (dt, J = 1.6, 8.4 Hz, 1H), 7.20 (dt, J =
1.2, 8.4 Hz, 1H), 6.99 (t, J = 8.4 Hz, 2H); 13C NMR (100 MHz,
CDCl3): δ 166.5, 163.9, 151.9, 140.3, 133.9, 132.6, 131.9, 129.9, 129.4,
124.8, 122.8, 120.5, 116.4, 116.2. Anal. Calcd for C18H14FN3O2S: C,
60.83; H, 3.97; N, 11.82. Found: C, 60.68; H, 4.05; N, 11.59. IR (KBr,
cm−1): 3275, 3094, 2932, 1587, 1455, 1325, 1165, 1092, 931, 780, 692,
536.
2-(4-Chlorophenylsulfonamido)azobenzene (3c). Yield 86% (31.9
mg); pale yellow solid, mp 94−95 °C; 1H NMR (400 MHz, CDCl3): δ
9.77 (s, 1H), 7.81 (dd, J = 2.4, 8.0 Hz, 2H), 7.76 (dd, J = 1.6, 8.0 Hz,
1H), 7.72−7.69 (m, 3H), 7.55−7.53 (m, 3H), 7.41 (dt, J = 1.6, 8.4 Hz,
1H), 7.27 (d, J = 8.4 Hz, 2H), 7.20 (dt, J = 1.2, 8.4 Hz, 1H); 13C NMR
(100 MHz, CDCl3): δ 151.9, 140.3, 139.7, 137.5, 133.9, 132.6, 131.9,
129.4, 128.5, 124.9, 123.0, 122.8, 120.6. Anal. Calcd for C18H14-
ClN3O2S: C, 58.14; H, 3.79; N, 11.30. Found: C, 58.43; H, 3.65; N,
11.52. IR (KBr, cm−1): 3258, 3062, 2917, 1575, 1495, 1332, 1160,
1088, 920, 795, 693, 530.
2-(4-Bromophenylsulfonamido)azobenzene (3d). Yield 82% (34.1
mg); pale yellow solid, mp 143−144 °C; 1H NMR (400 MHz,
CDCl3): δ 9.77 (s, 1H), 7.82−7.76 (m, 3H), 7.70 (dd, J = 1.2, 8.4 Hz,
1H), 7.62 (dd, J = 2.0, 7.2 Hz, 2H), 7.63−7.54 (m, 3H), 7.49−7.39
(m, 3H), 7.21 (dt, J = 1.2, 8.4 Hz, 1H); 13C NMR (100 MHz, CDCl3):
δ 151.7, 140.3, 138.0, 133.8, 132.6, 132.3, 131.9, 129.4, 128.6, 124.8,
123.1, 122.8, 120.5. Anal. Calcd for C18H14BrN3O2S: C, 51.93; H,
3.39; N, 10.09. Found: C, 52.11; H, 3.25; N, 9.88. IR (KBr, cm−1):
3265, 3097, 2915, 1578, 1501, 1376, 1330, 1164, 1091, 745, 648, 528.
2-(3-Nitrophenylsulfonamido)azobenzene (3e). Yield 76% (29.1
mg); pale yellow solid, mp 102−104 °C; 1H NMR (400 MHz,
CDCl3): δ 9.71 (s, 1H), 8.63−8.61 (m, 1H), 8.26−8.23 (m, 1H),
8.01−7.98 (m, 1H), 7.78−7.72 (m, 4H), 7.54−7.51 (m, 4H), 7.49−
7.44 (m, 1H), 7.27−7.23 (m, 1H); 13C NMR (100 MHz, CDCl3): δ
151.7, 148.1, 141.0, 140.8, 133.2, 132.7, 132.4, 132.2, 130.8, 130.3,
129.5, 127.5, 125.7, 122.8, 122.7, 122.4, 121.5. Anal. Calcd for
C18H14N4O4S: C, 56.54; H, 3.69; N, 14.65. Found: C, 56.75; H, 3.87;
N, 14.37. IR (KBr, cm−1): 3282, 3075, 2940, 1588, 1344, 1172, 1094,
834, 671, 534.
2-(Phenylsulfonamido)azobenzene (3g). Yield 75% (25.3 mg);
1
pale yellow solid, mp 108−109 °C; H NMR (300 MHz, CDCl3): δ
9.81 (s, 1H, NH), 7.82−7.79 (m, 4H), 7.74 (dt, J = 0.9, 7.2 Hz, 2H),
7.55−7.51 (m, 3H), 7.46−7.39 (m, 2H), 7.34 (t, J = 6.0 Hz, 2H), 7.16
(dt, J = 0.9, 6.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): δ 151.9, 140.1,
139.1, 134.3, 133.1, 132.5, 131.8, 129.3, 129.0, 127.1, 124.4, 122.8,
122.8, 120.3. HRMS (ESI) m/z: Calcd for C18H16N3O2S [M + H]+
338.0958, found 338.0962. IR (KBr, cm−1): 3248, 1580, 1453, 1335,
1154, 1068, 918, 775, 693, 550.
2-(4-tert-Butylphenylsulfonamido)azobenzene (3h). Yield 93%
1
(36.5 mg); pale yellow solid, mp 132−133 °C; H NMR (400 MHz,
CDCl3): δ 9.74 (s, 1H), 7.81−7.78 (m, 3H), 7.76−7.71 (m, 3H),
7.55−7.51 (m, 3H), 7.41 (dt, J = 1.6, 8.4 Hz, 1H), 7.35 (d, J = 1.6 Hz,
2H), 7.16 (dt, J = 1.2, 8.4 Hz, 1H), 1.21 (s, 9H); 13C NMR (100 MHz,
CDCl3): δ 156.9, 151.9, 140.0, 136.2, 134.6, 132.6, 131.7, 129.3, 127.0,
126.1, 124.2, 122.8, 122.6, 120.2, 35.1, 30.9. HRMS (ESI) m/z: Calcd
for C22H24N3O2S [M + H]+ 394.1584, found 394.1588. IR (KBr,
cm−1): 3249, 2961, 1502, 1338, 1164, 1092, 910, 768, 685, 520.
2-(4-Methoxyphenylsulfonamido)azobenzene (3i). Yield 92%
(33.8 mg); pale yellow solid, mp 108−109 °C; 1H NMR (400
MHz, CDCl3): δ 9.71 (s, 1H), 7.82 (t, J = 2.4 Hz, 2H), 7.74−7.69 (m,
4H), 7.52 (dd, J = 1.2, 4.4 Hz, 3H), 7.38 (t, J = 8.4 Hz, 1H), 7.15 (t, J
= 8.4 Hz, 1H), 6.77 (dd, J = 2.0, 6.8 Hz, 2H), 3.72 (s, 3H); 13C NMR
(100 MHz, CDCl3): δ 163.2, 151.9, 140.1, 134.6, 132.5, 131.7, 130.6,
129.3, 128.2, 124.3, 122.8, 122.6, 120.2, 114.2, 55.5. HRMS (ESI) m/z:
Calcd for C19H18N3O3S [M + H]+ 368.1063, found 368.1068. IR
(KBr, cm−1): 3315, 2925, 2840, 1594, 1495, 1332, 1268, 1152, 1097,
893, 792, 685, 537.
2-(2-Naphthylsulfonamido)azobenzene (3j). Yield 89% (34.4
mg); pale yellow solid, mp 93−94 °C; 1H NMR (400 MHz,
CDCl3): δ 9.94 (s, 1H), 8.42 (s, 1H), 7.82−7.69 (m, 8H), 7.56−7.49
(m, 5H), 7.37 (t, J = 8.4 Hz, 1H), 7.12 (t, J = 8.4 Hz, 1H); 13C NMR
(100 MHz, CDCl3): δ 151.9, 140.0, 136.0, 134.9, 134.2, 132.6, 131.9,
131.7, 129.4, 129.3, 129.2, 128.9, 128.8, 127.9, 127.5, 124.4, 123.0,
122.8, 122.0, 120.2. Anal. Calcd for C22H17N3O2S: C, 68.20; H, 4.42;
N, 10.85. Found: C, 67.98; H, 4.51; N, 10.77. IR (KBr, cm−1): 3263,
3062, 2922, 2853, 1586, 1464, 1295, 1152, 1092, 927, 767, 684, 543.
2-(2-Thienylsulfonamido)azobenzene (3k). Yield 94% (32.2 mg);
1
pale yellow solid, mp 132−134 °C; H NMR (300 MHz, CDCl3): δ
9.83 (s, 1H, NH), 7.86−7.79 (m, 4H), 7.56 (dd, J = 4.2, 9.6 Hz, 4H),
7.46 (dd, J = 4.8, 7.2 Hz, 1H), 7.27−7.19 (m, 1H), 6.92 (t, J = 3.6 Hz,
1H), 4.12 (dd, J = 7.2, 14.4 Hz, 1H); 13C NMR (75 MHz, CDCl3): δ
151.9, 140.4, 139.6, 134.2, 132.8, 132.6, 131.8, 129.3, 127.3, 124.8,
122.9, 122.6, 120.6. Anal. Calcd for C16H13N3O2S2: C, 55.96; H, 3.82;
N, 12.24. Found: C, 56.05; H, 3.94; N, 12.05. IR (KBr, cm−1): 3255,
3105, 3075, 1586, 1407, 1253, 1083, 927, 834, 714, 683.
2-(Butylsulfonamido)azobenzene (3l). Yield 96% (30.4 mg); pale
1
yellow solid, mp 72−74 °C; H NMR (400 MHz, CDCl3): δ 9.61 (s,
1H), 7.92−7.87 (m, 3H), 7.78 (dd, J = 1.2, 8.4 Hz, 1H), 7.57−7.51
(m, 3H), 7.47 (dt, J = 1.2, 8.4 Hz, 1H), 7.23 (t, J = 8.4 Hz, 1H), 3.17−
3.14 (m, 2H), 1.81−1.73 (m, 2H), 1.36 (q, J = 7.2 Hz, 2H), 0.81 (t, J =
7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): δ 151.9, 139.2, 134.9,
132.9, 131.8, 129.4, 123.9, 123.2, 122.8, 118.6, 51.7, 25.4, 21.3, 13.4.
Anal. Calcd for C16H19N3O2S: C, 60.54; H, 6.04; N, 13.24. Found: C,
60.73; H, 6.18; N, 13.05. IR (KBr, cm−1): 3264, 2953, 2865, 1502,
1378, 1335, 1154, 923, 782, 648, 531.
2-(4-Methylphenylsulfonamido)-4,4′-dichloroazobenzene (4a).
1
Yield 55% (23.1 mg); pale yellow solid, mp 165−167 °C; H NMR
(300 MHz, CDCl3): δ 9.82 (s, 1H), 7.78−7.69 (m, 6H), 7.52 (dd, J =
2.1, 6.6 Hz, 2H), 7.21 (d, J = 8.1 Hz, 2H), 7.12 (dd, J = 2.1, 8.4 Hz,
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Note
1H), 2.35 (s, 3H); 13C NMR (75 MHz, CDCl3): δ 150.2, 144.5, 138.9,
138.0, 135.9, 135.4, 129.9, 129.8, 129.7, 127.2, 124.4, 124.2, 124.0,
119.5, 21.5. Anal. Calcd for C19H15Cl2N3O2S: C, 54.29; H, 3.60; N,
10.00. Found: C, 54.45; H, 3.38; N, 10.12. IR (KBr, cm−1): 3248,
3086, 2926, 1578, 1534, 1356, 1143, 1085, 978, 834, 650.
Hz, 2H), 6.67 (dd, J = 2.7, 9.0 Hz, 1H), 3.86 (s, 3H), 2.45 (s, 3H),
2.33 (s, 3H); 13C NMR (75 MHz, CDCl3): δ 162.6, 149.9, 144.0,
141.5, 136.3, 135.54, 134.1, 129.9, 129.7, 127.2, 126.9, 122.3, 110.6,
103.5, 55.7, 29.7, 21.5. Anal. Calcd for C21H21N3O3S: C, 63.78; H,
5.35; N, 10.63. Found: C, 63.59; H, 5.44; N, 10.72. IR (KBr, cm−1):
3278, 3062, 2922, 2849, 1508, 1378, 1142, 1087, 837, 698, 548.
2-(4-Methylphenylsulfonamido)-4-methoxy-4′-bromoazo-
benzene (4i). Yield 40% (18.4 mg); pale yellow solid, mp 143−145
2-(4-Methylphenylsulfonamido)-4,4′-difluoroazobenzene (4b).
1
Yield 60% (29.2 mg); pale yellow solid, mp 160−161 °C; H NMR
(400 MHz, CDCl3): δ 10.41 (s, 1H), 7.84 (dt, J = 2.0, 6.8 Hz, 2H),
7.79−7.73 (m, 3H), 7.42 (dd, J = 2.4, 7.5 Hz, 1H), 7.26−7.20 (m,
4H), 6.85−6.80 (m, 1H), 2.35 (s, 3H); 13C NMR (100 MHz, CDCl3):
δ 166.0, 163.5, 148.2, 144.4, 136.0, 129.9, 127.2, 126.1, 125.9, 124.8,
124.7, 116.5, 111.4, 106.4, 21.6. Anal. Calcd for C19H15F2N3O2S: C,
58.91; H, 3.90; N, 10.85. Found: C, 59.05; H, 3.81; N, 10.92. IR (KBr,
cm−1): 3284, 3095, 2924, 1598, 1535, 1178, 1092, 972, 848, 735, 645.
2-(4-Methylphenylsulfonamido)-4,4′-di(trifluoromethoxy)azo-
benzene (4c). Yield 46% (23.9 mg); pale yellow solid, mp 115−116
°C; 1H NMR (400 MHz, CDCl3): δ 9.04 (s, 1H), 7.78 (d, J = 9.2 Hz,
2H), 7.66 (d, J = 8.0 Hz, 2H), 7.58 (d, J = 8.4 Hz, 3H), 7.40 (d, J = 8.4
Hz, 1H), 7.31 (dd, J = 1.2, 8.8 Hz, 1H), 7.16 (d, J = 8.0 Hz, 2H), 2.35
(s, 3H); 13C NMR (100 MHz, CDCl3): δ 152.8, 150.0, 145.7, 144.5,
140.7, 135.8, 134.1, 130.6, 129.8, 127.1, 125.5, 124.2, 122.2, 119.1,
114.5, 113.1, 21.5. Anal. Calcd for C21H15F6N3O4S: C, 48.56; H, 2.91;
N, 8.09. Found: C, 48.69; H, 3.02; N, 7.94. IR (KBr, cm−1): 3252,
3107, 2895, 1580, 1364, 1258, 1092, 854, 738, 640, 551.
1
°C; H NMR (400 MHz, CDCl3): δ 10.48 (s, 1H), 7.74−7.71 (m,
3H), 7.64 (dt, J = 2.8, 8.8 Hz, 4H), 7.19−7.14 (m, 3H), 6.67 (dd, J =
2.8, 8.8 Hz, 1H), 3.86 (s, 3H), 2.33 (s, 3H); 13C NMR (100 MHz,
CDCl3): δ 163.2, 150.6, 144.2, 136.3, 135.9, 134.0, 132.5, 129.7, 127.7,
127.2, 125.1, 123.8, 110.8, 103.4, 55.8, 21.5. Anal. Calcd for
C20H18BrN3O3S: C, 52.18; H, 3.94; N, 9.13. Found: C, 52.32; H,
3.87; N, 9.02. IR (KBr, cm−1): 3280, 3061, 2855, 1574, 1158, 1085,
968, 842, 647, 552.
2-(4-Methylphenylsulfonamido)-4-methoxy-4′-chloroazo-
benzene (4j). Yield 50% (20.7 mg); pale yellow solid, mp 142−143
1
°C; H NMR (400 MHz, CDCl3): δ 10.48 (s, 1H), 7.74−7.71 (m,
5H), 7.47 (dd, J = 2.0, 6.8 Hz, 4H), 7.19 (s, 1H), 7.18 (d, J = 6.8 Hz,
2H), 6.67 (dd, J = 2.8, 8.8 Hz, 1H), 3.86 (s, 3H), 2.33 (s, 3H); 13C
NMR (100 MHz, CDCl3): δ 163.2, 150.3, 144.2, 136.7, 136.3, 135.9,
134.0, 129.7, 129.6, 129.5, 127.2, 123.5, 110.8, 103.4, 55.8, 21.5.
HRMS (ESI) m/z: Calcd for C20H19ClN3O3S [M + H]+ 416.0830,
found 416.0836. IR (KBr, cm−1): 3281, 3058, 2925, 1575, 1358, 1162,
1086, 975, 834, 658, 560.
2-(4-Methylphenylsulfonamido)-4,4′-dimethylazobenzene (4d).
1
Yield 65% (24.6 mg); pale yellow solid, mp 161−162 °C; H NMR
2-(4-Methylphenylsulfonamido)-5,5′-dinitroazobenzene (4k).
(300 MHz, CDCl3): δ 9.98 (s, 1H), 7.73−7.63 (m, 5H), 7.53 (s, 1H),
7.33 (d, J = 8.1 Hz, 2H), 7.14 (d, J = 8.1 Hz, 2H), 6.99 (dd, J = 1.2, 8.1
Hz, 1H), 2.47 (s, 3H), 2.39 (s, 3H), 2.31 (s, 3H); 13C NMR (75 MHz,
CDCl3): δ 150.0, 143.9, 143.2, 142.1, 138.1, 136.3, 133.9, 129.9, 129.6,
127.1, 125.2, 123.3, 122.6, 120.3, 21.9, 21.6, 21.5. Anal. Calcd for
C21H21N3O2S: C, 66.47; H, 5.58; N, 11.07. Found: C, 66.58; H, 5.45;
N, 11.24. IR (KBr, cm−1): 2963, 2856, 1665, 1605, 1582, 1499, 1330,
1154, 1085, 905, 825, 658.
1
Yield 35% (15.4 mg); pale yellow solid, mp 213−215 °C; H NMR
(400 MHz, CDCl3): δ 9.87 (s, 1H), 8.70 (d, J = 2.4 Hz, 1H), 8.67 (t, J
= 2.0 Hz, 1H), 8.45 (dd, J = 1.6, 6.0 Hz, 1H), 8.30 (dd, J = 2.8, 9.2 Hz,
1H), 8.25 (d, J = 8.8 Hz, 1H), 7.87−7.79 (m, 4H), 7.30 (d, J = 8.4 Hz,
2H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 151.9, 149.2,
145.3, 143.4, 140.3,137.8, 135.6, 130.6, 130.2, 129.2, 127.8, 127.3,
126.5, 118.6, 118.5, 117.3, 21.6. Anal. Calcd for C19H15N5O6S: C,
51.70; H, 3.43; N, 15.87. Found: C, 51.82; H, 3.51; N, 15.76. IR (KBr,
cm−1): 3295, 2948, 2871, 1532, 1389, 1165, 1089, 825, 654.
2-(4-Methylphenylsulfonamido)-4,4′-dimethoxyazobenzene (4e).
1
Yield 45% (28.8 mg); pale yellow solid, mp 114−115 °C; H NMR
(400 MHz, CDCl3): δ 10.54 (s, 1H), 7.78 (d, J = 8.8 Hz, 2H), 7.70
(dd, J = 5.6, 8.8 Hz, 3H), 7.19 (d, J = 2.4 Hz, 1H), 7.16 (d, J = 8.0 Hz,
2H), 7.00 (d, J = 8.8 Hz, 2H), 6.65 (dd, J = 2.4, 8.8 Hz, 1H), 3.90 (s,
3H), 3.84 (s, 3H), 2.31 (s, 3H); 13C NMR (100 MHz, CDCl3): δ
162.3, 162.0, 146.1, 143.9, 136.3, 135.3, 134.2, 129.7, 127.2, 126.4,
124.2, 114.4, 110.6, 103.6, 55.7, 55.6, 21.5. HRMS (ESI) m/z: Calcd
for C21H22N3O4S [M + H]+ 412.1326, found 412.1327. IR (KBr,
cm−1): 3265, 3098, 2954, 1592, 1248, 1175, 1086, 945, 832, 740, 652,
539.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H and 13C NMR spectra of all products. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jxfliu@163.com.
■
2-(4-Methylphenylsulfonamido)-5,5′-dimethylazobenzene (4f).
1
Yield 95% (36.0 mg); pale yellow solid, mp 107−108 °C; H NMR
(300 MHz, CDCl3): δ 9.49 (s, 1H), 7.66−7.59 (m, 5H), 7.54 (d, J =
1.5 Hz, 1H), 7.44 (d, J = 7.8 Hz, 1H), 7.33 (d, J = 7.8 Hz, 1H), 7.22
(dd, J = 1.5, 8.1 Hz, 1H), 7.11 (d, J = 7.8 Hz, 2H), 2.49 (s, 3H), 2.34
(s, 3H), 2.29 (s, 3H); 13C NMR (75 MHz, CDCl3): δ 152.1, 143.8,
140.3, 139.2, 136.1, 134.4, 133.2, 132.4, 132.0, 129.6, 129.1, 127.1,
123.2, 122.4, 120.8, 120.1, 29.7, 21.5, 20.8. HRMS (ESI) m/z: Calcd
for C21H22N3O2S [M + H]+ 380.1427, found 380.1432. IR (KBr,
cm−1): 3278, 2923, 2854, 1512, 1385, 1165, 1082, 812, 642.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Science Foundation
(No. 872011, 872022) and the Startup Fund for Advanced
Talents (No. 833158) of Shanxi Normal University.
2-(4-Methoxyphenylsulfonamido)-5,5′-dimethylazobenzene
1
(4g). Yield 98% (38.7 mg); pale yellow solid, mp 102−104 °C; H
REFERENCES
■
NMR (300 MHz, CDCl3): δ 9.46 (s, 1H), 7.68 (dd, J = 1.8, 7.8 Hz,
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(dd, J = 1.8, 7.2 Hz, 2H), 3.73 (s, 3H), 2.48 (s, 3H), 2.34 (s, 3H); 13C
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396.1376, found 396.1378. IR (KBr, cm−1): 3275, 2920, 2855, 1532,
1172, 1085, 940, 835, 742, 653, 540.
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