Palladium-catalyzed ortho-functionalization of azoarenes with aryl acylperoxides

Article abstract of DOI:10.1039/c4ob00993b

With the aid of an azo directing group, Pd-catalyzed ortho-sp² C-H bond activation/functionalization of azoarenes with aryl acyl peroxides has been explored. This transformation provides easy access to regioselectively introducing acyloxyl and aryl groups into azoarenes by simply changing the reaction temperature and solvent. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00993b

Organic &
Biomolecular Chemistry
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Palladium-catalyzed ortho-functionalization of
azoarenes with aryl acylperoxides†
Cite this: Org. Biomol. Chem., 2014,
12, 5866
Cheng Qian,a Dongen Lin,a Yuanfu Deng,a Xiao-Qi Zhang,b Huanfeng Jiang,a
Guang Miao,a Xihao Tanga and Wei Zeng*a
With the aid of an azo directing group, Pd-catalyzed ortho-sp2 C–H bond activation/functionalization of
azoarenes with aryl acyl peroxides has been explored. This transformation provides easy access to regio-
selectively introducing acyloxyl and aryl groups into azoarenes by simply changing the reaction tempera-
ture and solvent.
Received 13th May 2014,
Accepted 9th June 2014
DOI: 10.1039/c4ob00993b
www.rsc.org/obc
Introduction
Regioselective installation of special functional groups into
aromatic molecules is one of the most attractive and challen-
ging hot topics in organic chemistry. Recently, much effort
has been made to develop transition metal-catalyzed C–H
functionalization with the chelation assistance of a directing
group.1 Among them, aromatic sp2 C–H activation/oxygenation
has attracted increasing attention due to that hydroxylated
arenes have been widely employed as fundamental building
blocks of many pharmaceuticals and biologically natural
compounds.2
Recently, several elegant studies have demonstrated that
pyridine,3 amide,4 oxime ether,5 pyrimidine6 group, etc. could
be used as an anchor to form cyclopalladated intermediates,
which could further react with coupling partners including
PhI(OAc)2,3a–h,k–m carboxylic acids,4–6 alcohols,3j,5a and acid
anhydrides7 to realize the C–H activation/oxygenation reac-
tions via C–O bond forming reductive elimination. However,
although significant attention has been focused on the above-
mentioned directing groups, there are rare reported cases of
using the azo group as a directing group to accelerate the C–H
activation/functionalization process.3a,8 More recently, we
found that the Pd(OAc)2/TBHP system could efficiently catalyze
a cascade oxidation/sp2 C–H bond acylation of azoarenes with
aryl methanes or alcohols, and its mechanism was proposed
to be involved in an oxidative addition process between palla-
dacyclic intermediate (A) and acyl radical (B) (Scheme 1a).9
Based on this work and considering that acyl peroxides (C)
could easily produce acyloxyl radical (D) or aryl radical (E) via
Scheme 1 Pd-catalyzed ortho-functionalization of azoarenes.
homolysis under heating conditions,10 herein we reported, for
the first time, that Pd-catalyzed sp2 C–H acyloxylation and
arylation of azoarenes with aryl acylperoxides could concisely
construct ortho-acyloxylated azoarenes (E) (Scheme 1b).
Results and discussion
The acyloxylation of azobezene (1a) (0.15 mmol) with benzoyl
peroxide (2a) (0.30 mmol) was initially chosen as a model reac-
tion to optimize the reaction parameters. At first, this trans-
formation was carried out at 60 °C in the presence of PdCl2
(10 mol%) for 24 h to screen the various solvents (Table 1,
entries 1–7), and we quickly found that CH3CN could provide
us the desired ortho-acyloxylated product (3a) in 43% yield
(entry 7). Subsequently, a further screening of Pd salts indi-
cated that Pd(OAc)2 was the best catalyst which could lead
to the formation of 3a in 82% yield (compare entries 7–9 with
10). To our surprise, when we investigated the effect of the
reaction temperature on this transformation, we accidentally
found that higher reaction temperature (80 °C) could also lead
to the formation of 16% yield of arylated product (4a) besides
3a (59%) (compare entries 10 and 11 with 12). So, we contin-
ued to further optimize the reaction solvent and the reaction
temperature (entries 12–17), and finally the Pd-catalyzed ortho-
functionalization of azobenzene with benzoyl peroxide could
aSchool of Chemistry and Chemical Engineering, South China University of
Technology, Guangzhou 510641, P. R. China. E-mail: zengwei@scut.edu.cn
bJinan University, Guangzhou 510641, P. R. China
†Electronic supplementary information (ESI) available: Detailed experimental
procedures and characterization of products. See DOI: 10.1039/c4ob00993b
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Table 1 Optimization of the Pd-catalyzed ortho-functionalization of
azobenzene with benzoyl peroxidea
Table 2 Pd-catalyzed ortho-acyloxylation of azoarenes with aryl
acylperoxidesa
Entry
PdX2
Solvent
Temp. (°C)
3a/4a yieldb (%)
1
2
3
4
5
6
7
8
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
Pd(TFA)2
Pd(MeCN)2Cl2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
DMSO
CH2Cl2
THF
Toluene
PhCF3
PhCl
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
PhCF3
PhCl
60
60
60
60
60
60
60
60
60
60
40
80
80
Trace/0
26/0
14/0
34/0
37/0
31/0
43/0
60/0
33/0
82/0
67/0
59/16
54/21
48/26
0/70
0/76
0/74
9
10
11
12
13
14
15
16
17
80
PhCl
PhCl
PhCl
120
130
135
a All the reactions were carried out using azobenzene (1a) (0.15 mmol)
and benzoylperoxide (2a) (0.30 mmol) with Pd catalyst (10 mol%) in
solvent (2.0 mL) for 24 h under air conditions in a sealed tube,
followed by flash chromatography on SiO2. b Isolated yield.
afford another sole ortho-aryl product 4a in 76% yield using
chlorobenzene as a solvent at 130 °C for 24 h (entry 16).
After we established an efficient reaction protocol that
enables the ortho-acyloxylation of azobenzene with benzoyl
peroxide, the scope of this transformation with regard to
azoarenes and aryl acylperoxides was first explored. As shown
in Table 2, although the C–H acyloxylation of substituted
azoarenes with peroxides could proceed smoothly and furnish
the corresponding acyloxylated products, the substitution on
the benzene ring of azoarenes and acyl peroxides showed sig-
nificant electronic effects. The substrates with a para-electron
donating group (4-H, 4-MeO and 4-Me) on the azophenyl and
acylphenyl rings afforded the desired products in moderate to
good yields (3a, 3b, 3e and 3p). It is noteworthy that the ortho-
substituted azobenzene (1d) and meta- or ortho-substituted
aryl acyl peroxide (2c and 2d) gave poorer yield of product
(3d, 3n, 3o) because of higher steric hindrance (compare 3b,
3m and 3c with 3d, 3n and 3o). In contrast, the electron-poor
azoarenes or aryl acylperoxides with 4-Cl, 4-Br, 4-F and 4-NO2
groups on the phenyl ring afforded the desired products in
moderate to poor yields (3f–3h and 3q–3s). Unfortunately, the
substrate 1i with the 4-CO2Et group did not produce the corres-
ponding acyloxylated product (3i), possibly due to its low reac-
tivity. Moreover, we also investigated the electronic effect of
various substituents on the regioselectivity of ortho-acyloxyla-
tion of unsymmetric azoarenes, and found that ortho-acyloxyla-
tion reactions took place mainly on the electron-rich azo
aromatic rings, possibly due to the fact that the electron-rich
phenyl ring easily nucleophilically attacks the Pd(II) and leads
a The mixture of azoarenes (1) (0.15 mmol) and peroxides (2) (2.0
equiv.) was stirred in the presence of Pd(OAc)2 (10 mol%) in CH3CN
(2.0 mL) at 60 °C for 24 h under air conditions in a sealed tube,
followed by flash chromatography on SiO2. b Isolated yield. c The ratio
of trans to cis diastereomers was determined by 1H NMR spectroscopy.
d The ratio of trans to cis diastereomers was not provided.
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to the formation of cyclopalladium intermediate via C–H acti-
vation (compare 3j with 3k and 3l). Similarly, for the unsym-
metric aryl acylperoxide 2i, the electron-rich (4-Me-phenyl)-
acyloxy group is also more reactive than the electron-poor
(4-Cl-phenyl)-acyloxy group. It is worth noting that unsym-
metric acylperoxide 2j only produced phenylacyloxylated azo-
benzene 3a in 67% yield. At last, we tried to use acetyl
peroxide 2k as an acyloxyl source, but no desired product (3t)
was observed under our reaction conditions.
Table 3 Pd-catalyzed ortho-arylation of azoarenes with aryl
acylperoxidesa
Subsequently, the above-mentioned substrates were con-
tinuously employed in the Pd-catalyzed ortho-arylation of
azoarenes using chlorobenzene as a solvent at 130 °C. As
shown in Table 3, the reaction properties including the substi-
tuent electronic effects, the “ortho-substituent” effect and
regioselectivity of unsymmetric azoarenes and acylperoxides
are similar to the ortho-acyloxylation of azoarenes with aryl
acylperoxides.11
ortho-Hydroxy azoarene and ortho-hydroxy hydrazoarene
derivatives belong to useful intermediates in pharmaceutical
and dye industries.12 ortho-Acyloxylated arene 3a could be
easily hydrolyzed and reduced to produce the corresponding
ortho-hydroxyl azobenzene 5 (91% yield) and ortho-phenyl-
acyloxyl hydrazobenzene
6
(82% yield), respectively
(Scheme 2a). Moreover, we further found ortho-acyoxlylated
azobenzene 3a could also be converted to N-phenyl-benzamide
7 (71% yield) and 2-amino-phenol 8 (64% yield) under Zn/
NH4Cl conditions at 80 °C via a cascade reduction/nucleophi-
lic substitution (Scheme 2b).
To further probe the reaction mechanism, we ran the
Pd-catalyzed C–H acyloxyation of azobenzene with benzoyl
peroxide in the presence of TEMPO under our reaction con-
ditions. Unfortunately, no acyloxylated 3a was observed possi-
bly due to the fact that TEMPO suppressed the formation of
phenyl acyloxy radical (Scheme 3a). And also, when acyloxy-
lated product 3a was employed as the starting material and
stirred at 130 °C for 24 h in the presence of Pd(OAc)2, we did
not observe the formation of 4a by the GC-MS method; these
controlled experiments indicated that a radical process was
involved in this reaction system, and the possibility that 3a
could be directly converted to 4a via a decarboxylation process
was also ruled out (Scheme 3b).
Taking previous reports on Pd-catalyzed sp2 C–H acylation
into account,13 and in combination with the results from the
above-mentioned controlled reactions, we proposed a plausible
reaction mechanism for this transformation (see Fig. 1), in
which Pd(OAc)2 reacted with azobenzene (1a) by sp2 C–H acti-
vation to form a palladacyclic intermediate A.13b Then A
reacted with acyloxyl B or phenyl radical C which was in situ-
homolysed from benzoyl peroxide under heating conditions to
produce either Pd(IV)14 or Pd(III)15 species D. Finally, the
species D underwent reductive elimination to afford the acyl-
oxyated or arylated product D with the release of the Pd(II)
species. In addition to the above-mentioned radical mechan-
ism, an alternative reaction pathway involving the oxidation of
Pd(II) to Pd(IV) by aryl acyl peroxide via a two-electron process
cannot be ruled out.
a The mixture of azoarenes (1) (0.15 mmol) and peroxides (2) (2.0
equiv.) was stirred at 130 °C in the presence of Pd(OAc)2 (10 mol %) in
PhCl (2.0 mL) for 24 h under air conditions in a sealed tube, followed
by flash chromatography on SiO2. b Isolated yield. c The ratio of trans to
cis diastereomers was determined by 1H NMR spectroscopy. d The ratio
of trans to cis diastereomers was not provided.
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ting patterns that could not be interpreted or easily visualized
are designated as multiple (m). Low resolution mass spectra
were recorded using a mass spectrometer. High resolution
mass spectra (HRMS) were recorded on an IF-TOF spectro-
meter (Micromass). Gas chromatography mass spectra were
obtained with a model spectrometer.
Scheme 2 Synthetic application of this transformation.
General procedure for the synthesis of 1b–1i
A mixture containing aniline derivatives (5 mmol), CuBr
(0.3 mmol), pyridine (0.9 mmol), and 10 mL of toluene was
stirred vigorously at 60 °C under air for 24 h. After cooling
down to room temperature and concentrating under vacuum,
the residue was purified by flash chromatography (hexanes) to
get the products.
(E)-1,2-Di-p-tolyldiazene
(1b).16 Yellow
solid;
mp
Scheme 3 Control reactions.
1
142–143 °C; 456 mg, 87% yield; H NMR (400 MHz, CDCl3) δ
7.81 (d, J = 8.2 Hz, 4H), 7.30 (d, J = 8.1 Hz, 4H), 2.42 (s, 6H);
13C NMR (100 MHz, CDCl3) δ 150.9, 141.2, 129.7, 122.7, 21.5;
MS (EI, 70 eV) m/z: 210.01 (M+).
(E)-1,2-Di-m-tolyldiazene (1c).16 Yellow solid; mp 55–56 °C;
1
451 mg, 86% yield; H NMR (400 MHz, CDCl3) δ 7.72 (s, 4H),
7.40 (t, J = 7.9 Hz, 2H), 7.28 (d, J = 7.4 Hz, 2H), 2.46 (s, 6H); 13
C
NMR (100 MHz, CDCl3) δ 152.8, 138.9, 131.6, 128.9, 122.9,
120.4, 21.3; MS (EI, 70 eV) m/z: 210.10 (M+).
(E)-1,2-Di-o-tolyldiazene (1d).16 Yellow solid; mp 56–57 °C;
288 mg, 55% yield; 1H NMR (400 MHz, CDCl3) δ 7.61 (d, J =
7.9 Hz, 2H), 7.32 (d, J = 2.8 Hz, 4H), 7.26–7.23 (m, 2H), 2.73 (s,
6H); 13C NMR (100 MHz, CDCl3) δ 151.1, 138.0, 131.3, 130.7,
126.4, 115.9, 17.6; MS (EI, 70 eV) m/z: 209.99 (M+).
Fig. 1 The proposed reaction mechanism.
(E)-1,2-Bis(4-methoxyphenyl)diazene (1e).16 Yellow solid;
mp 142–143 °C; 338 mg, 56% yield; 1H NMR (400 MHz, CDCl3)
δ 7.88 (d, J = 8.9 Hz, 4H), 7.00 (d, J = 8.9 Hz, 4H), 3.88 (s, 6H);
13C NMR (100 MHz, CDCl3) δ 161.5, 147.0, 124.3, 114.1, 55.5;
MS (EI, 70 eV) m/z: 242.06 (M+).
Conclusion
In summary, we have developed a Pd(II)-catalyzed sp2 C–H
functionalization of azoarenes with aryl acylperoxides under
mild conditions. This protocol provided easy access to the syn-
thesis of various ortho-acyloxylated azoarenes and ortho-aryl
azoarene derivatives by simply changing the reaction solvent
and the reaction temperature.
(E)-1,2-Bis(4-chlorophenyl)diazene (1f).16 Yellow solid; mp
166–168 °C; 518 mg, 83% yield; 1H NMR (400 MHz, CDCl3)
δ 7.86 (d, J = 8.6 Hz, 4H), 7.49 (d, J = 8.6 Hz, 4H); 13C NMR
(100 MHz, CDCl3) δ 150.8, 137.2, 129.4, 124.2; MS (EI, 70 eV)
m/z: 250.03 (M+).
(E)-1,2-Bis(4-bromophenyl)diazene (1g).16 Yellow solid; mp
132–134 °C; 480 mg, 54% yield; 1H NMR (400 MHz, CDCl3)
δ 7.82–7.77 (m, 4H), 7.66 (dd, J = 6.5, 4.6 Hz, 4H); 13C NMR
Experimental section
General information
Unless otherwise noted, reactions were conducted in dry sol- (100 MHz, CDCl3) δ 151.1, 132.4, 125.7, 124.4; MS (EI, 70 eV)
vents. Purifications of reaction products were carried out by m/z: 337.45 (M+).
flash chromatography using silica gel (40–63 mm). Infrared
(E)-1,2-Bis(4-fluorophenyl)diazene (1h).16 Yellow solid; mp
spectra (IR) were recorded on a 400 MHz spectrometer and are 102–104 °C; 476 mg, 87% yield; 1H NMR (400 MHz, CDCl3)
reported as wavelength numbers (cm−1). Infrared spectra were δ 8.01–7.91 (m, 4H), 7.22 (t, J = 8.4 Hz, 4H); 13C NMR
recorded by preparing a KBr pellet containing the title com- (100 MHz, CDCl3) δ 165.6, 163.1, 149.0, 124.8, 124.7, 116.1,
pound. 1H and 13C NMR spectra were recorded with tetra- 115.9; MS (EI, 70 eV) m/z: 218.95 (M+).
methylsilane (TMS) as an internal standard at ambient
(E)-Diethyl 4,4′-(diazene-1,2-diyl)dibenzoate (1i).16 Yellow
temperature unless otherwise indicated on 400 MHz for 1H solid; mp 128–130 °C; 417 mg, 51% yield; H NMR (400 MHz,
NMR and 100 MHz for 13C NMR. Chemical shifts are reported CDCl3) δ 8.21 (d, J = 8.4 Hz, 4H), 7.98 (d, J = 8.4 Hz, 4H), 4.43
in parts per million (ppm) and coupling constants are (q, J = 7.1 Hz, 4H), 1.43 (t, J = 7.1 Hz, 6H); 13C NMR (100 MHz,
reported as hertz (Hz). Splitting patterns are designated as CDCl3) δ 165.9, 154.8, 132.7, 130.6, 122.8, 61.3, 14.3; MS
singlet (s), broad singlet (bs), doublet (d), and triplet (t). Split- (EI, 70 eV) m/z: 326.95 (M+).
1
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Procedure for the synthesis of 1j. The mixture of CuBr 7.6 Hz, 1H), 7.49 (t, J = 7.7 Hz, 2H), 2.27 (s, 3H); 13C NMR
(2.9 mg, 0.02 mmol), pyridine (4.8 mg, 0.06 mmol), aniline (100 MHz, CDCl3) δ 166.19, 162.96, 134.26, 129.73, 128.83,
(93 mg,
0.2 mmol) in toluene (4 mL) was vigorously stirred at 60 °C 1770, 1591, 1448, 1371, 1231, 1169, 1011, 890, 838, 700 cm−1
under O2 (1 atm) for 24 h. Then cooling down to room temp- Procedure for the synthesis of 2k. Hydrogen peroxide
erature and concentrating in vacuum, the residue was purified (510 mg, 5 mmol) was added dropwise over 10 min to a cold
by flash chromatography (hexanes) on silica gel to afford 1j. (ice bath) solution of acetyl chloride (780 mg, 10 mmol) in
1
mmol) and 4-methoxybenzenamine (25 mg, 125.58, 16.69; MS (EI, 70 eV) m/z: 180.1 (M+); IR (KBr): 2974,
.
(E)-1-(4-Methoxyphenyl)-2-phenyldiazene (1j).16 Yellow solid; diethyl ether (10 mL). This was followed by the dropwise
mp 56–58 °C; 19 mg, 45% yield; 1H NMR (400 MHz, CDCl3) addition of an aqueous solution of NaOH (400 mg, 10 mmol)
δ 7.94–7.90 (m, 2H), 7.88 (dd, J = 5.2, 3.4 Hz, 2H), 7.49 (dd, over 10 min. The resulting white precipitate was collected by
J = 10.1, 4.7 Hz, 2H), 7.45–7.39 (m, 1H), 7.01–6.98 (m, 2H), filtration and then was purified by flash chromatography
3.85 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 162.1, 152.8, (hexanes–ethyl acetate 40 : 1).10c
147.0, 130.4, 129.0, 124.8, 122.6, 114.2, 55.6; MS (EI, 70 eV)
Acetic peroxyanhydride (2k).19 White oil; 64% yield;
1H NMR (400 MHz, CDCl3) δ 2.10 (s, 6H); 13C NMR (100 MHz,
m/z: 212.3 (M+).
Procedure for the synthesis of 1k. The mixture of CuBr CDCl3) δ 177.66, 20.71; MS (EI, 70 eV) m/z: 118.2 (M+); IR (KBr):
(2.9 mg, 0.02 mmol), pyridine (4.8 mg, 0.06 mmol), p-toluidine 2907, 1812, 1754, 1375, 1352, 1415 cm−1
(93 mg, mmol) and 4-methoxybenzenamine (25 mg,
.
1
0.2 mmol) in toluene (4 mL) was vigorously stirred at 60 °C
under O2 (1 atm) for 24 h. Then cooling down to room temp-
General procedure for the synthesis of 3a–3r
erature and concentrating in a vacuum, the residue was A 10 mL reaction tube was charged with aromatic azo com-
purified by flash chromatography (hexanes) on silica gel to pound (1) (0.15 mmol), aryl acylperoxide (2) (0.30 mmol),
afford 1k.
Pd(OAc)2 (10 mol%), and CH3CN (2.0 mL). After the reaction
(E)-1-(4-Methoxyphenyl)-2-(p-tolyl)diazene
(1k).16 Yellow was carried out at 60 °C for 24 h, it was cooled to room temp-
1
solid; mp 109–111 °C; 20 mg, 44% yield; H NMR (400 MHz, erature and concentrated in vacuum. The residue was purified
CDCl3) δ 7.90 (d, J = 8.9 Hz, 2H), 7.79 (d, J = 8.3 Hz, 2H), 7.29 by flash chromatography (hexanes–ethyl acetate 100 : 1) to
(d, J = 8.1 Hz, 2H), 7.00 (d, J = 8.9 Hz, 2H), 3.88 (s, 3H), 2.42 (s, afford the desired products.
3H); 13C NMR (100 MHz, CDCl3) δ 161.8, 150.8, 147.1, 140.8,
(E)-2-(Phenyldiazenyl)phenyl benzoate (3a). Yellow solid;
1
129.6, 124.5, 122.7, 122.5, 114.1, 55.5, 21.4; MS (EI, 70 eV) m/z: mp 91–93 °C; 36 mg, 82% yield; H NMR (400 MHz, CDCl3) δ
226.2 (M+).
8.27 (d, J = 7.6 Hz, 2H), 7.90–7.84 (m, 1H), 7.71–7.67 (m, 2H),
Procedure for the synthesis of 2i. Hydrogen peroxide 7.65 (d, J = 7.5 Hz, 1H), 7.58–7.49 (m, 3H), 7.38 (q, J = 6.5 Hz,
(250 mg, 10 mmol) was added dropwise over 10 min to a cold 5H); 13C NMR (100 MHz, CDCl3) δ 165.5, 152.7, 149.2, 143.9,
(ice bath) solution of p-toluoylchloride (750 mg, 5 mmol) and 133.6, 132.0, 131.2, 130.3, 128.9, 128.6, 126.5, 123.5, 123.0,
para-chlorobenzoylchloride (850 mg, 5 mol) in diethyl ether 117.8; HR-MS (EI) calcd for [M
(10 mL). This was followed by the dropwise addition of an 325.0947, found 325.0939; IR (KBr): 3063, 2924, 2853, 2361,
aqueous solution of NaOH (200 mg, 10 mmol) over 10 min. 1521, 1418, 1258, 1150, 1077, 1022, 999, 842, 752, 521 cm−1
The resulting white precipitate was collected by filtration, and (E)-5-Methyl-2-(p-tolyldiazenyl)phenyl benzoate (3b). Yellow
then purified by flash chromatography (hexanes–ethyl acetate solid; mp 90–92 °C; 34 mg, 68% yield; 1H NMR (400 MHz,
30 : 1) to get the desired products.10c
CDCl3) δ 8.25 (d, J = 7.5 Hz, 2H), 7.78 (d, J = 8.7 Hz, 1H), 7.65
+
Na]+: C19H14N2O2Na
.
4-Chlorobenzoic 4-methylbenzoic peroxyanhydride (2i). (t, J = 7.4 Hz, 1H), 7.57 (d, J = 8.2 Hz, 2H), 7.53 (t, J = 7.7 Hz,
White solid; mp 119–121 °C; 38% yield; 1H NMR (400 MHz, 2H), 7.16 (dd, J = 13.5, 7.5 Hz, 4H), 2.45 (s, 3H), 2.34 (s, 3H);
CDCl3) δ 8.05–7.99 (m, 2H), 7.96 (d, J = 8.2 Hz, 2H), 7.53–7.47 13C NMR (100 MHz, CDCl3) δ 165.5, 151.0, 149.0, 142.7, 141.9,
(m, 2H), 7.31 (d, J = 8.0 Hz, 2H), 2.45 (s, 3H); 13C NMR 141.4, 133.4, 130.3, 129.6, 129.5, 128.5, 127.3, 123.8, 122.8,
(100 MHz, CDCl3) δ 163.0, 162.3, 145.4, 140.9, 131.1, 129.8, 117.6; HR-MS (EI) calcd for [M
129.6, 129.3, 124.1, 122.5, 21.8; HR-MS (EI) calcd for [M]+: 353.1260, found 353.1272; IR (KBr): 3689, 3031, 2852, 1868,
C15H11ClO4 290.0346, found 290.0341; IR (KBr): 3852, 3739, 1831, 1600, 1492, 1339, 1176, 1144, 1058, 818, 766, 545 cm−1
3618, 2922, 2862, 2360, 1754, 1231, 996, 740, 475 cm−1
(E)-4-Methyl-2-(m-tolyldiazenyl)phenyl benzoate (3c). Yellow
+
Na]+: C21H18N2O2Na
.
.
Procedure for the synthesis of 2j. Acetyl chloride (780 mg, solid; mp 78–79 °C; 33 mg, 65% yield; 1H NMR (400 MHz,
10 mmol) and perbenzoic acid (1520 mg, 11 mmol) were CDCl3) δ 8.27 (t, J = 8.0 Hz, 2H), 7.69–7.61 (m, 2H), 7.51 (dd,
added to 15 mL diethyl ether, the mixture was cooled with an J = 13.2, 5.8 Hz, 3H), 7.44 (s, 1H), 7.37–7.32 (m, 1H), 7.30–7.21
ice–water bath and pyridine (880 mg, 11 mmol) was added (m, 2H), 7.18 (d, J = 7.4 Hz, 1H), 2.44 (s, 3H), 2.24 (s, 3H); 13C
dropwise. After the addition, the reaction mixture was stirred NMR (100 MHz, CDCl3) δ = 165.7, 152.9, 147.2, 143.4, 138.7,
for an additional 45 min, washed twice with 5% HCl, twice 136.4, 133.4, 132.6, 131.8, 130.3, 128.5, 122.9, 120.8, 117.9,
with 5% NaHCO3, and twice with distilled water, respectively, 21.1, 21.0; HR-MS (EI) calcd for [M + Na]+: C21H18N2O2Na
to get the desired product.17
353.1260, found 353.1274; IR (KBr): 3060, 2992, 2853, 2359,
Aceticbenzoic peroxyanhydride (2j).18 White oil; 40% yield; 1784, 1711, 1692, 1659, 1484, 1457, 1380, 1131, 1108, 914, 740,
1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 8.2 Hz, 2H), 7.64 (t, J = 687, 588 cm−1
.
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(E)-3-Methyl-2-(o-tolyldiazenyl)phenyl benzoate (3d). Yellow 7.38–7.32 (m, 3H), 6.92 (dd, J = 13.0, 2.5 Hz, 2H), 3.91 (s, 3H);
solid; mp 71–73 °C; 21 mg, 41% yield; 1H NMR (400 MHz, 13C NMR (100 MHz, CDCl3) δ 162.9, 152.8, 150.9, 133.6, 130.5,
CDCl3) δ 8.14–8.10 (m, 2H), 7.59 (t, J = 7.5 Hz, 1H), 7.48–7.41 130.4, 128.8, 128.6, 122.7, 119.0, 112.8, 108.2, 55.8; HR-MS (EI)
(m, 2H), 7.39 (d, J = 8.1 Hz, 1H), 7.34 (t, J = 7.8 Hz, 1H), 7.24 (s, calcd for [M + Na]+: C20H16N2O3Na 355.1053, found 355.1065;
1H), 7.17 (dd, J = 13.2, 7.7 Hz, 3H), 7.08 (dd, J = 15.1, 7.1 Hz, IR (KBr): 2864, 2812, 2354, 1864, 1832, 1542, 1479, 1097, 983,
1H), 2.55 (s, 3H), 2.37 (s, 3H); 13C NMR (100 MHz, CDCl3) 681, 453, 398 cm−1
δ 165.3, 151.3, 143.7, 142.8, 138.30, 134.7, 133.3, 131.0, 130.2, (E)-2-((4-Methoxyphenyl)diazenyl)-5-methylphenyl benzoate
.
129.4, 129.2, 128.4, 126.1, 121.5, 115.1, 19.3, 17.4; HR-MS (EI) (3l) and (E)-5-methoxy-2-(p-tolyldiazenyl)phenyl benzoate
calcd for [M + Na]+: C21H18N2O2Na 353.1260, found 353.1277; (3k). Red oil; 29 mg, 56% yield; 1H NMR (400 MHz, CDCl3)
IR (KBr): 3704, 2359, 2339, 1785, 1663, 1552, 1483, 1002, 749, δ 8.26 (d, J = 7.6 Hz, 4H), 7.89 (d, J = 8.7 Hz, 1H), 7.77 (d, J =
670, 653, 510 cm−1
.
8.6 Hz, 1H), 7.66 (dd, J = 5.7, 3.1 Hz, 4H), 7.52 (dd, J = 19.4,
(E)-5-Methoxy-2-((4-methoxyphenyl)diazenyl)phenyl benzo- 12.3 Hz, 6H), 7.17 (d, J = 4.0 Hz, 2H), 7.11 (t, J = 10.1 Hz, 2H),
ate (3e). Yellow solid; mp 125–127 °C; 41 mg, 75% yield; 1H 6.96–6.89 (m, 2H), 6.85 (d, J = 8.8 Hz, 2H), 3.90 (s, 3H), 3.82 (s,
NMR (400 MHz, CDCl3) δ 8.27 (d, J = 7.8 Hz, 2H), 7.87 (d, J = 3H), 2.45 (s, 3H), 2.34 (s, 3H); 13C NMR (100 MHz, CDCl3)
8.8 Hz, 1H), 7.71–7.60 (m, 3H), 7.53 (dd, J = 15.6, 7.8 Hz, 2H), δ 162.6, 162.0, 150.7, 148.7, 147.2, 142.3, 141.0, 138.1, 133.5,
6.90 (dd, J = 11.7, 2.5 Hz, 2H), 6.83 (d, J = 8.9 Hz, 2H), 3.90 (s, 133.4, 130.4, 130.3, 129.5, 128.6, 127.3, 124.7, 123.8, 122.7,
3H), 3.81 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 165.4, 162.3, 118.9, 117.6, 114.0, 112.8, 108.1, 55.8, 55.5; HR-MS (EI) calcd
161.7, 150.3, 147.3, 138.2, 133.5, 130.3, 128.4, 124.5, 118.9, for [M + Na]+: C21H18N2O3Na 369.1210, found 369.1189; IR
114.0, 112.8, 108.1, 55.8, 55.4; HR-MS (EI) calcd for [M + Na]+: (KBr): 3740, 3696, 3630, 2923, 2360, 1900, 1860, 1530, 1500,
C21H18N2O4Na 385.1159, found 385.1131; IR (KBr): 3433, 2921, 1462, 1295, 1179, 1104, 710, 540 cm−1
2851, 2361, 1795, 1558, 1345, 1257, 1173, 1069, 685, 550 cm−1
(E)-2-(Phenyldiazenyl)phenyl 4-methylbenzoate (3m). Yellow
(E)-5-Chloro-2-((4-chlorophenyl)diazenyl)phenyl benzoate solid; mp 101–103 °C; 26 mg, 56% yield; H NMR (400 MHz,
.
.
1
(3f). Red oil; 23 mg, 41% yield; 1H NMR (400 MHz, CDCl3) CDCl3) δ 8.15 (d, J = 8.2 Hz, 2H), 7.89–7.84 (m, 1H), 7.74–7.68
δ 8.22 (t, J = 8.4 Hz, 2H), 7.82 (d, J = 8.7 Hz, 1H), 7.68 (t, J = (m, 2H), 7.57–7.50 (m, 1H), 7.38 (td, J = 5.8, 2.5 Hz, 5H), 7.33
7.4 Hz, 1H), 7.63–7.58 (m, 1H), 7.52 (dt, J = 13.6, 7.7 Hz, 2H), (d, J = 8.0 Hz, 2H), 2.46 (s, 3H); 13C NMR (100 MHz, CDCl3)
7.42 (dd, J = 5.0, 2.7 Hz, 2H), 7.33 (dd, J = 9.9, 5.4 Hz, 2H), 7.24 δ 165.5, 152.7, 149.3, 144.4, 144.0, 132.0, 130.6, 130.4, 129.3,
(dd, J = 16.1, 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 165.1, 128.9, 126.4, 123.6, 123.0, 117.7, 21.8; HR-MS (EI) calcd for
150.9, 149.7, 142.4, 137.5, 133.9, 133.5, 130.4, 129.5, 128.7, [M + Na]+: C20H16N2O2Na 339.1104, found 339.1106; IR (KBr):
127.0, 125.8, 124.2, 121.7, 118.7; HR-MS (EI) calcd for 3445, 2027, 1832, 1736, 1648, 1260, 1130, 992, 750, 638,
[M + Na]+: C19H12Cl2N2O2Na 393.0168, found 393.0183; IR 616 cm−1
.
(KBr): 3736, 3673, 3446, 2852, 1699, 1541, 1477, 1402, 1199,
1110, 890, 766, 652, 526 cm−1
(E)-5-Bromo-2-((4-bromophenyl)diazenyl)phenyl
(E)-2-(Phenyldiazenyl)phenyl 3-methylbenzoate (3n). Oil;
27 mg, 42% yield; 1H NMR (400 MHz, CDCl3) δ 7.98 (d, J =
benzoate 8.4 Hz, 2H), 7.79 (d, J = 8.2 Hz, 1H), 7.64 (d, J = 7.0 Hz, 2H),
.
1
(3g). Yellow solid; mp 143–145 °C; 28 mg, 42% yield; H NMR 7.46 (t, J = 7.7 Hz, 1H), 7.38 (d, J = 7.4 Hz, 1H), 7.34–7.29 (m,
(400 MHz, CDCl3) δ 8.22 (t, J = 7.2 Hz, 2H), 7.75 (d, J = 8.6 Hz, 6H), 2.36 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 165.64, 152.77,
1H), 7.71–7.61 (m, 2H), 7.58–7.48 (m, 5H), 7.43 (t, J = 7.0 Hz, 149.33, 144.05, 138.44, 134.37, 132.03, 131.21, 130.88, 128.52,
1H), 7.25–7.18 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 165.2, 127.55, 126.51, 123.57, 117.80, 21.30; HR-MS (EI) calcd for
151.3, 151.0, 149.7, 142.8, 133.5, 132.3, 130.1, 129.5, 128.5, [M + H]+: C20H17N2O2 317.1284, found 317.1287; IR (KBr):
127.0, 125.8, 124.4, 121.7, 118.9; HR-MS (EI) calcd for [M]+: 3357, 2017, 1798, 1725, 1643, 1317, 1287, 1230, 1109, 746, 639,
C19H12Br2N2O2 457.9260, found 457.9261; IR (KBr): 3652, 620 cm−1
3315, 2913, 2894, 1632, 1526, 1436, 1418, 846, 768, 459 cm−1
(E)-2-(Phenyldiazenyl)phenyl
(E)-5-Fluoro-2-((4-fluorophenyl)diazenyl)phenyl
benzoate Yellow solid; mp 99–101 °C; 28 mg, 55% yield; 1H NMR
.
.
4-methoxybenzoate
(3p).
(3h). Yellow solid; mp 78–79 °C; 18 mg, 35% yield; 1H NMR (400 MHz, CDCl3) δ 8.22 (d, J = 8.5 Hz, 2H), 7.87 (d, J = 8.4 Hz,
(400 MHz, CDCl3) δ 8.27 (dt, J = 5.9, 2.8 Hz, 2H), 7.96–7.88 (m, 1H), 7.72 (d, J = 6.6 Hz, 2H), 7.54 (t, J = 7.6 Hz, 1H), 7.39 (s,
1H), 7.76–7.67 (m, 3H), 7.58 (t, J = 7.7 Hz, 2H), 7.21–7.11 (m, 5H), 7.01 (d, J = 8.5 Hz, 2H), 3.91 (s, 3H); 13C NMR (100 MHz,
2H), 7.05 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 165.7 (d, 2J(C,F) CDCl3) δ 165.20, 163.93, 152.73, 149.39, 144.10, 132.51, 132.02,
2
= 8.9 Hz), 165.1 (d, J(C,F) = 9.1 Hz), 163.2, 150.4, 140.6, 133.9, 131.17, 128.98, 126.41, 123.67, 123.05, 117.71, 113.89, 55.54;
130.4, 128.7, 124.9, 119.2, 116.1, 115.8, 113.9, 113.7, 111.4, HR-MS (EI) calcd for [M + Na]+: C20H16N2O3Na 355.1053,
111.1; HR-MS (EI) calcd for [M + Na]+: C19H12F2N2O2Na found 355.0871; IR (KBr): 2922, 2360, 2339, 1739, 1610, 1484,
361.0759, found 361.0769; IR (KBr): 2919, 2851, 2589, 2283, 1452, 1208, 1192, 1056, 835, 741, 544 cm−1
.
1592, 1530, 1513, 1497, 1451, 1093, 1052, 750, 702, 531,
413 cm−1
(E)-2-((4-Methoxyphenyl)diazenyl)phenyl
(E)-2-(Phenyldiazenyl)phenyl 4-fluorobenzoate (3q). Yellow
oil; 20 mg, 42% yield; H NMR (400 MHz, CDCl3) δ 8.33–8.24
(3j). (m, 2H), 7.88 (dd, J = 8.0, 1.4 Hz, 1H), 7.71–7.67 (m, 2H),
1
.
benzoate
Yellow solid; mp 114–115 °C; 31 mg, 63% yield; 1H NMR 7.58–7.51 (m, 1H), 7.43–7.35 (m, 5H), 7.23–7.17 (m, 2H); 13C
(400 MHz, CDCl3) δ 8.27 (d, J = 7.3 Hz, 2H), 7.91 (d, J = 8.8 Hz, NMR (100 MHz, CDCl3) δ 164.9, 164.5, 152.6, 149.0, 143.9,
1H), 7.71–7.60 (m, 3H), 7.53 (dd, J = 15.8, 8.1 Hz, 2H), 133.0, 132.9, 132.0, 131.3, 129.0, 126.6, 123.4, 123.0, 117.9,
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115.9, 115.7; HR-MS (EI) calcd for [M + Na]+: C19H13FN2O2Na 287.1541; IR (KBr): 3434, 2920, 2851, 1636, 1475, 1275, 1219,
343.0853, found 343.0862; IR (KBr): 2921, 2851, 2360, 2338, 765, 697, 476 cm−1
1741, 1504, 1478, 1412, 1195, 1060, 819, 716, 684, 622, (E)-1-(3-Methyl-[1,1′-biphenyl]-2-yl)-2-(o-tolyl)diazene
507 cm−1 Red oil; 19 mg, 40% yield; 1H NMR (400 MHz, CDCl3) δ
.
(4d).
.
(E)-2-(Phenyldiazenyl)phenyl 4-chlorobenzoate (3r). Yellow 7.34–7.27 (m, 7H), 7.25–7.22 (m, 3H), 7.21–7.12 (m, 2H), 2.43
solid; mp 74–76 °C; 24 mg, 48% yield; 1H NMR (400 MHz, (s, 3H), 2.33 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 150.9, 140.2,
CDCl3) δ 8.22–8.17 (m, 2H), 7.88 (dd, J = 8.0, 1.5 Hz, 1H), 138.2, 135.9, 131.2, 130.9, 130.7, 130.3, 129.0, 127.9, 127.8,
7.72–7.66 (m, 2H), 7.56–7.49 (m, 3H), 7.43–7.36 (m, 5H); 13C 126.5, 126.2, 115.2, 19.2, 17.1; HR-MS (EI) calcd for [M + H]+:
NMR (100 MHz, CDCl3) δ 164.6, 152.6, 149.0, 143.8, 140.1, C20H19N2 287.1543, found 287.1543; IR (KBr): 3433, 3056,
132.0, 131.7, 131.3, 129.0, 127.8, 126.7, 123.4, 123.0, 117.9; 2853, 1943, 1734, 1540, 1443, 766, 699, 577, 454 cm−1
HR-MS (EI) calcd for [M + Na]+: C19H12ClN2O2Na 359.0558,
(E)-5-Methoxy-2-((5-methoxy-[1,1′-biphenyl]-2-yl)diazenyl)-
found 359.0567; IR (KBr): 3105, 2956, 1612, 1500, 1209, 615, phenol (4e). Yellow solid; mp 132–134 °C; 37 mg, 75% yield;
593, 495 cm−1 1H NMR (400 MHz, CDCl3) δ 14.55 (s, 1H), 7.57 (d, J = 9.0 Hz,
.
.
(E)-2-(Phenyldiazenyl)phenyl 4-nitrobenzoate (3s). Yellow 3H), 7.50 (d, J = 6.5 Hz, 2H), 7.47–7.39 (m, 4H), 6.93 (t, J =
1
solid; mp 154–156 °C; 12 mg, 23% yield; H NMR (400 MHz, 8.9 Hz, 2H), 6.62 (d, J = 2.7 Hz, 1H), 6.49 (d, J = 2.6 Hz, 1H),
CDCl3) δ 8.43 (d, J = 8.6 Hz, 2H), 8.37 (d, J = 8.7 Hz, 2H), 7.89 3.89 (s, 3H), 3.84 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 163.0,
(d, J = 8.0 Hz, 1H), 7.67 (d, J = 7.9 Hz, 2H), 7.57 (t, J = 7.7 Hz, 161.1, 156.9, 146.0, 144.5, 139.2, 130.7, 127.4, 123.4, 114.4,
1H), 7.45–7.34 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 163.6, 109.4, 100.8, 55.6, 55.5; HR-MS (EI) calcd for [M − H]−:
152.6, 150.9, 148.6, 143.6, 134.8, 132.1, 131.5, 131.4, 129.0, C20H17N2O3 333.1245, found 333.1252; IR (KBr): 3852, 3739,
127.1, 123.8, 123.1, 122.9, 118.2; HR-MS (EI) calcd for [M]+: 2925, 2360, 1605, 1485, 1203, 1030, 835, 831, 757, 670,
C19H13N3O4 347.0901, found 347.0902; IR (KBr): 3435, 2920, 526 cm−1
.
1744, 1641, 1613, 1348, 1258, 837, 686, 500 cm−1
.
(E)-1-(5-Chloro-[1,1′-biphenyl]-2-yl)-2-(4-chloro phenyl)-
1
diazene (4f). Yellow solid; mp 91–93 °C; 23 mg, 47% yield; H
NMR (400 MHz, CDCl3) δ 7.85 (t, J = 7.7 Hz, 1H), 7.72 (dd, J =
General procedure for the synthesis of 4a–4r
A 10 mL reaction tube was charged with aromatic azo com- 13.7, 8.7 Hz, 2H), 7.58 (d, J = 2.2 Hz, 1H), 7.51–7.39 (m, 8H);
pound (1) (0.15 mmol), aryl acylperoxide (2) (0.30 mmol), 13C NMR (100 MHz, CDCl3) δ 151.0, 150.8, 147.7, 142.9, 137.4,
Pd(OAc)2 (10 mol%), and PhCl (1.0 mL). After the reaction was 137.1, 136.9, 130.7, 129.4, 129.3, 128.2, 127.8, 127.8, 124.5,
carried out at 130 °C for 24 h, it was cooled to room tempera- 124.2, 117.3; HR-MS (EI) calcd for [M]+: C18H12Cl2N2 326.0372,
ture and concentrated in vacuum. The residue was purified by found 326.0371; IR (KBr): 3694, 3683, 3472, 2921, 2850, 1725,
flash chromatography (hexanes) to afford the desired products. 1710, 1690, 1403, 1383, 1257, 1171, 960, 883, 656, 572, 482,
(E)-1-([1,1′-Biphenyl]-2-yl)-2-phenyldiazene
solid; mp 78–80 °C; 30 mg, 76% yield; 1H NMR (400 MHz,
(4a).20 Yellow 414 cm−1
.
(E)-1-(5-Bromo-[1,1′-biphenyl]-2-yl)-2-(4-bromo phenyl)-
CDCl3) δ 7.76 (dt, J = 21.8, 10.1 Hz, 3H), 7.59 (d, J = 7.5 Hz, diazene (4g). Yellow solid; mp 143–142 °C; 22 mg, 38% yield;
1H), 7.54 (t, J = 7.3 Hz, 1H), 7.48–7.38 (m, 9H); 13C NMR 1H NMR (400 MHz, CDCl3) δ 7.71–7.66 (m, 1H), 7.58 (dd, J =
(100 MHz, CDCl3) δ 152.8, 149.7, 141.1, 138.8, 130.9, 130.8, 20.6, 12.0 Hz, 4H), 7.53–7.49 (m, 2H), 7.37 (d, J = 8.8 Hz, 5H);
130.8, 129.0, 128.0, 127.6, 127.2, 123.2, 115.9; MS (EI, 70 eV) 13C NMR (100 MHz, CDCl3) δ 151.4, 148.1, 143.1, 137.3, 133.7,
m/z: 258.1 (M+); IR (KBr): 3687, 3498, 2879, 1792, 1834, 1823, 132.4, 131.1, 130.7, 127.8, 127.8, 124.7, 124.4, 117.5; HR-MS
1532, 1512, 982, 534 cm−1
(E)-1-(5-Methyl-[1,1′-biphenyl]-2-yl)-2-(p-tolyl)diazene
.
(EI) calcd for [M + H]+: C18H13Br2N2 414.2811, found 414.2802;
(4b). IR (KBr): 3682, 3637, 2340, 1765, 1725, 1493, 1479, 1414, 1270,
Yellow solid; mp 76–78 °C; 30 mg, 70% yield; 1H NMR 1147, 749, 688, 484 cm−1
.
(400 MHz, CDCl3) δ 7.68 (dd, J = 8.0, 5.1 Hz, 3H), 7.47 (d, J =
(E)-1-(5-Fluoro-[1,1′-biphenyl]-2-yl)-2-(4-fluoro phenyl)-
7.6 Hz, 2H), 7.44–7.36 (m, 4H), 7.30 (d, J = 8.0 Hz, 1H), 7.21 (d, diazene (4h). Yellow solid; mp 77–78 °C; 15 mg, 34% yield; 1H
J = 12.8 Hz, 2H), 2.47 (s, 3H), 2.40 (s, 3H); 13C NMR (100 MHz, NMR (400 MHz, CDCl3) δ 7.82 (ddd, J = 19.2, 8.8, 5.5 Hz, 3H),
CDCl3) δ 151.1, 147.8, 141.1, 140.9, 139.0, 131.3, 130.9, 129.6, 7.47 (dd, J = 7.7, 2.4 Hz, 4H), 7.32 (ddd, J = 12.7, 5.9, 3.5 Hz,
128.8, 127.5, 127.1, 123.1, 122.7, 115.7, 21.4, 21.4; HR-MS (EI) 2H), 7.17 (dt, J = 14.9, 5.7 Hz, 3H); 13C NMR (100 MHz, CDCl3)
2
2
calcd for [M + H]+: C20H19N2 287.1543, found 287.1548; IR δ 165.5 (d, J(C,F) = 17.9 Hz), 163.0 (d, J(C,F) = 17.4 Hz), 149.3,
(KBr): 3711, 3546, 2921, 1828, 1600, 1457, 1103, 766, 580, 145.9, 143.7, 137.8, 130.7, 127.7, 125.2, 125.1, 118.0, 117.9,
540 cm−1
.
117.3, 117.0, 116.1, 115.9, 115.3, 115.0; HR-MS (EI) calcd for
(E)-1-(4-Methyl-[1,1′-biphenyl]-2-yl)-2-(m-tolyl)diazene (4c). [M + H]+: C18H13F2N2 295.1041, found 295.1039; IR (KBr):
Yellow solid; mp 70–72 °C; 24 mg, 57% yield; 1H NMR 3673, 3446, 1649, 1541, 1222, 1199, 1101, 1081, 995, 893, 765,
(400 MHz, CDCl3) δ 7.62–7.56 (m, 2H), 7.54 (s, 1H), 7.50–7.44 700, 578, 524 cm−1
.
(m, 3H), 7.41 (t, J = 7.2 Hz, 2H), 7.39–7.32 (m, 3H), 7.24 (d, J =
(E)-Ethyl 6-((4-(ethoxycarbonyl)phenyl)diazenyl)-[1,1′-biphe-
4.9 Hz, 1H), 2.46 (s, 3H), 2.40 (s, 3H); 13C NMR (100 MHz, nyl]-3-carboxylate (4i). Yellow solid; mp 115–117 °C; 18 mg,
CDCl3) δ 153.0, 149.6, 138.9, 138.8, 138.3, 138.0, 131.6, 130.9, 29% yield; 1H NMR (400 MHz, CDCl3) δ 8.30 (d, J = 1.6 Hz,
130.6, 128.8, 127.5, 127.0, 124.0, 120.2, 116.1, 21.3, 21.1; 1H), 8.13 (dd, J = 13.8, 5.2 Hz, 3H), 7.83 (d, J = 8.5 Hz, 2H),
HR-MS (EI) calcd for [M + H]+: C20H19N2 287.1543, found 7.77 (d, J = 8.4 Hz, 1H), 7.51–7.42 (m, 5H), 4.42 (dq, J = 14.4,
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7.1 Hz, 4H), 1.42 (dt, J = 9.5, 7.1 Hz, 6H); 13C NMR (100 MHz, 123.2, 122.8, 120.4, 115.9, 114.6, 114.4; HR-MS (EI) calcd for
CDCl3) δ 165.9, 155.0, 152.0, 141.3, 137.8, 132.6, 132.3, 130.8, [M + H]+: C18H14FN2 277.1136, found 277.1135; IR (KBr):
130.6, 129.2, 127.8, 123.1, 116.0, 61.4, 61.3, 14.3, 14.3; HR-MS 2935, 2910, 2835, 1503, 1489, 1439, 1021, 998, 676, 654, 531,
(EI) calcd for [M + Na]+: C24H22N2O4Na 425.1472, found 493 cm−1
.
425.1487; IR (KBr): 3125, 2989, 1735, 1634, 1468, 1246, 1106,
1056, 846, 526 cm−1
(E)-1-(4′-Chloro-[1,1′-biphenyl]-2-yl)-2-phenyl diazene (4r).
Red oil; 25 mg, 56% yield; H NMR (400 MHz, CDCl3) δ 7.87
1
.
(E)-1-(5-Methoxy-[1,1′-biphenyl]-2-yl)-2-phenyl diazene (4j). (d, J = 7.1 Hz, 1H), 7.77 (t, J = 7.3 Hz, 3H), 7.54 (d, J = 3.7 Hz,
Red oil; 27 mg, 63% yield; 1H NMR (400 MHz, CDCl3) δ 8.23 (t, 2H), 7.47 (dd, J = 13.1, 6.1 Hz, 4H), 7.40 (s, 3H); 13C NMR
J = 10.4 Hz, 1H), 7.92 (d, J = 8.7 Hz, 2H), 7.88 (d, J = 7.5 Hz, (100 MHz, CDCl3) δ 152.8, 149.5, 140.0, 137.3, 132.1, 131.1,
2H), 7.51 (dd, J = 13.8, 6.9 Hz, 3H), 7.42 (d, J = 7.2 Hz, 2H), 130.9, 130.6, 129.3, 129.1, 128.4, 127.8, 123.2, 122.2, 116.0;
7.24–7.17 (m, 1H), 7.02 (d, J = 8.7 Hz, 2H), 3.89 (s, 3H); 13C HR-MS (EI) calcd for [M + H]+: C18H14ClN2 293.0840, found
NMR (100 MHz, CDCl3) δ 162.0, 147.0, 130.3, 129.0, 124.7, 293.0849; IR (KBr): 3433, 2924, 2360, 2340, 1744, 1589, 1260,
122.5, 114.2, 55.5; HR-MS (EI) calcd for [M + H]+: C19H17ON2 1176, 1056, 749, 655, 524 cm−1
289.1335, found 289.1330; IR (KBr): 3433, 3007, 2838, 2360,
.
Synthetic application for this transformation
1741, 1601, 1501, 1255, 1143, 1028, 837, 806, 751, 548 cm−1
.
(E)-1-(4-Methoxyphenyl)-2-(5-methyl-[1,1′-biphenyl]-2-yl)diazene (a) A mixture of 3a (0.15 mmol, 1 equiv.) and K2CO3
(4l) and (E)-1-(5-methoxy-[1,1′-biphenyl]-2-yl)-2-(p-tolyl)- (0.24 mmol, 1.6 equiv.) in NMP (2.0 mL) was heated at 100 °C
1
diazene (4k). Yellow solid; mp 76–78 °C; 70% yield; H NMR for 3 h under N2. It was cooled to room temperature and then
(400 MHz, CDCl3) δ 8.26 (d, J = 7.7 Hz, 3H), 7.89 (d, J = 8.6 Hz, purified by flash chromatography (hexanes) to get the desired
1H), 7.77 (d, J = 8.7 Hz, 1H), 7.66 (d, J = 8.7 Hz, 3H), 7.52 (dd, products.21
J = 15.5, 8.4 Hz, 5H), 7.17 (s, 2H), 7.12 (s, 1H), 6.91 (d, J =
(E)-2-(Phenyldiazenyl)phenol (5).22 Solid; mp 121–123 °C;
1
9.3 Hz, 1H), 6.85 (d, J = 8.7 Hz, 2H), 3.90 (s, 1.5H), 3.82 (s, 3H), 27 mg, 91% yield; H NMR (400 MHz, CDCl3) δ 12.92 (s, 1H),
2.45 (s, 3H), 2.34 (s, 1.5H); 13C NMR (100 MHz, CDCl3) δ 165.6, 7.95 (dd, J = 7.9, 1.6 Hz, 1H), 7.88 (dd, J = 8.2, 1.2 Hz, 2H),
165.5, 162.6, 162.0, 150.9, 148.7, 147.2, 142.3, 141.9, 141.0, 7.56–7.47 (m, 3H), 7.39–7.33 (m, 1H), 7.10–7.01 (m, 2H); 13C
133.5, 133.4, 130.3, 130.3, 129.6, 129.5, 128.5, 127.3, 124.7, NMR (100 MHz, CDCl3) δ 152.7, 137.3, 133.2, 133.2, 131.1,
123.8, 122.7, 118.9, 117.6, 114.0, 112.8, 108.1, 55.8, 55.5, 21.4, 129.3, 122.2, 119.9, 118.2; MS (EI, 70 eV) m/z: 198.1 (M+); IR
21.3; HR-MS (EI) calcd for [M]+: C20H18N2O 302.1419, found (KBr): 3411, 2977, 2898, 1649, 1449, 1057, 882, 770, 685,
302.1413; IR (KBr): 3687, 3541, 2913, 1815, 1584, 1435, 1128, 434 cm−1
754, 579, 526 cm−1
(b) A suspension of the azo compound 3a (0.2 mmol,
.
.
(E)-1-(4′-Methyl-[1,1′-biphenyl]-2-yl)-2-phenyl diazene (4m). 1 equiv.) and zinc dust (0.2 mmol, 1 equiv.) in methanol
Yellow solid; mp 78–79 °C; 29 mg, 70% yield; 1H NMR (3 mL) and ammonium chloride (0.4 mmol, 2 equiv.) was
(400 MHz, CDCl3) δ 7.80 (d, J = 7.4 Hz, 2H), 7.73 (d, J = 8.0 Hz, stirred under a nitrogen atmosphere at room temperature.
1H), 7.58 (d, J = 7.6 Hz, 1H), 7.52 (dd, J = 13.6, 5.9 Hz, 1H), After the completion of the reaction (monitored by TLC), the
7.49–7.40 (m, 5H), 7.37 (d, J = 7.9 Hz, 2H), 7.22 (d, J = 7.4 Hz, reaction mixture was filtered through a celite pad and washed
1H), 2.43 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 152.9, 149.8, with solvent. The combined filtrate and washings were concen-
141.0, 137.0, 135.8, 130.8, 129.0, 128.4, 127.8, 127.5, 123.2, trated, and the residue was dissolved in chloroform (5 mL) or
120.4, 115.9, 21.2; HR-MS (EI) calcd for [M + H]+: C19H17N2 diethyl ether and was washed with saturated brine solution
273.1386, found 273.1381; IR (KBr): 3738, 3615, 2921, 2850, (5 mL) and water. The organic layer was dried over anhydrous
1785, 1764, 1450, 1410, 1382, 1216, 961, 926, 513, 503 cm−1
(E)-1-(3′-methyl-[1,1′-biphenyl]-2-yl)-2-phenyl diazene (4n). by flash chromatography (hexanes–ethyl acetate 10 : 1).23
Oil; 23 mg, 43% yield; 1H NMR (400 MHz, CDCl3) δ 7.72 (d, J =
2-(2-Phenylhydrazinyl)phenyl benzoate (6). Solid; mp
.
magnesium sulfate and concentrated. The residue was purified
7.7 Hz, 2H), 7.67 (d, J = 8.0 Hz, 1H), 7.51 (d, J = 7.6 Hz, 1H), 86–88 °C; 50 mg, 82% yield; 1H NMR (400 MHz, CDCl3)
7.45 (t, J = 7.4 Hz, 1H), 7.37 (d, J = 7.5 Hz, 4H), 7.25–7.22 (m, δ 8.15–8.08 (m, 2H), 7.55 (dd, J = 10.6, 4.3 Hz, 1H), 7.42 (t, J =
2H), 7.18 (d, J = 9.5 Hz, 1H), 7.13 (d, J = 7.3 Hz, 1H), 2.34 (s, 7.7 Hz, 2H), 7.12 (dd, J = 13.3, 5.5 Hz, 2H), 7.04 (m, 3H),
3H); 13C NMR (100 MHz, CDCl3) δ 152.92, 149.79, 141.20, 6.80–6.72 (m, 4H), 5.71 (s, 1H), 5.46 (s, 1H); 13C NMR
138.73, 137.17, 131.63, 130.83, 130.76, 129.06, 128.25, 128.01, (100 MHz, CDCl3) δ 164.7, 148.5, 140.5, 137.0, 133.9, 130.2,
127.98, 127.48, 123.25, 115.92, 21.51; HR-MS (EI) calcd for 129.4, 128.7, 127.0, 122.4, 120.1, 119.6, 113.6, 112.4; HR-MS
[M + H]+: C19H17N2 273.1386, found 273.1386; IR (KBr): 3687, (EI) calcd for [M + Na]+: C19H16O2N2Na 327.1109, found
3642, 3605, 2931, 2819, 1797, 1748, 1449, 1435, 1368, 1209, 327.1075; IR (KBr): 3338, 2974, 2895, 2269, 1923, 1657, 1387,
943, 916, 498, 476 cm−1
(E)-1-(4′-Fluoro-[1,1′-biphenyl]-2-yl)-2-phenyl diazene (4q).
.
1050, 881, 695 cm−1
(c) A suspension of the azo compound 3a (0.2 mmol,
.
1
Red oil; 22 mg, 53% yield; H NMR (400 MHz, CDCl3) δ 7.92 1 equiv.) and zinc dust (0.2 mmol, 1 equiv.) in methanol
(d, J = 7.2 Hz, 1H), 7.82–7.70 (m, 2H), 7.58–7.52 (m, 3H), 7.45 (3 mL) and ammonium chloride (0.4 mmol, 2 equiv.) was
(dt, J = 8.5, 5.5 Hz, 5H), 7.12 (t, J = 8.7 Hz, 2H); 13C NMR stirred under a nitrogen atmosphere at 80 °C. After the com-
2
(100 MHz, CDCl3) δ 163.6, 161.2, 152.8 (d, J(C,F) = 11.7 Hz), pletion of the reaction (monitored by TLC), the reaction
149.6, 140.1, 132.4, 132.3, 131.3, 130.8, 130.7, 129.1, 128.1, mixture was filtered through a celite pad and washed with
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solvent. The combined filtrate and washings were concen-
trated, and the residue was dissolved in chloroform (5 mL) or
diethyl ether and was washed with saturated brine solution
(5 mL) and water. The organic layer was dried over anhydrous
magnesium sulfate and concentrated. The residue was purified
by flash chromatography (hexanes–ethyl acetate 10 : 1).23
N-Phenyl-benzamide (7).24 Solid; mp 163–165 °C; 28 mg,
3 (a) A. R. Dick, K. L. Hull and M. S. Sanford, J. Am. Chem.
Soc., 2004, 126, 2300; (b) A. R. Dick, J. W. Kampf and
M. S. Sanford, J. Am. Chem. Soc., 2005, 127, 12790;
(c) L. V. Desai, K. J. Stowers and M. S. Sanford, J. Am. Chem.
Soc., 2008, 130, 13285; (d) J. M. Racowski, A. R. Dick and
M. S. Sanford, J. Am. Chem. Soc., 2009, 131, 10974;
(e) N. Chernyak, A. S. Dudnik, C. Huang and V. Gevorgyan,
J. Am. Chem. Soc., 2010, 132, 8270; (f) D. Kalyani and
M. S. Sanford, Org. Lett., 2005, 7, 4149; (g) K. J. Stowers and
M. S. Sanford, Org. Lett., 2009, 11, 4584; (h) F. R. Gou,
X. C. Wang, P. F. Huo, H. P. Bi, Z. H. Guang and
Y. M. Liang, Org. Lett., 2009, 11, 5726; (i) D. A. Alonso,
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16, 5274; ( j) S. H. Kim, H. S. Lee, S. H. Kim and J. N. Kim,
Tetrahedron Lett., 2008, 49, 5863; (k) C. Huang,
N. Chernyak, A. Dudnik and V. Gevorgyan, Adv. Synth.
Catal., 2011, 353, 1285; (l) P. Y. Choy, C. P. Lau and
F. Y. Kwong, J. Org. Chem., 2011, 76, 80; (m) P. Y. Choy and
F. Y. Kwong, Org. Lett., 2013, 15, 270.
1
71% yield; H NMR (400 MHz, CDCl3) δ 7.93 (s, 1H), 7.8–7.82
(m, 2H), 7.64 (d, J = 7.6 Hz, 2H), 7.53 (m, 1H), 7.50–7.43 (m,
2H), 7.36 (dd, J = 10.8, 5.1 Hz, 2H), 7.15 (t, J = 7.4 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 165.8, 137.9, 135.0, 131.8, 129.0,
128.7, 127.0, 124.5, 120.2; MS (EI, 70 eV) m/z: 197.13 (M+); IR
(KBr): 3342, 2991, 2374, 1762, 1654, 1440, 1243, 924, 639,
498 cm−1
.
2-Aminophenol (8).25 Solid; mp 172–173 °C; 14 mg, 64%
1
yield; H NMR (400 MHz, CDCl3) δ 8.91 (s, 1H), 6.65 (dd, J =
7.7, 1.1 Hz, 1H), 6.59 (dd, J = 7.7, 1.7 Hz, 1H), 6.54 (td, J = 7.5,
1.2 Hz, 1H), 6.40 (td, J = 7.5, 1.7 Hz, 1H), 4.45 (s, 2H); MS (ESI):
m/z = 109 [M+].
4 G. W. Wang, T. T. Yuan and X. L. Wu, J. Org. Chem., 2008,
73, 4717.
The mechanism studies about this transformation
5 (a) L. V. Desai, L. H. Kami and M. S. Sanford, J. Am. Chem.
Soc., 2004, 126, 9542; (b) L. V. Desai, H. A. Malik and
M. S. Sanford, Org. Lett., 2006, 8, 1141.
6 S. Gu, C. Chen and W. Chen, J. Org. Chem., 2009, 74,
7203.
(a) A 10 mL reaction tube was charged with azobenzene (1a)
(0.15 mmol), benzoylperoxide (2a) (0.30 mmol), TEMPO
(0.15 mmol), Pd(OAc)2 (10 mol%), and CH3CN (2.0 mL). After
the reaction was carried out at 60 °C for 24 h, it was cooled to
room temperature. The reaction was monitored by GC-MS, and
no acyloxylated 3a was observed.
(b) A 10 mL reaction tube was charged with acyloxylated
product (3a) (0.15 mmol), Pd(OAc)2 (10 mol%), and PhCl
(1.0 mL). After the reaction was carried out at 130 °C for 24 h,
it was cooled to room temperature. The reaction was moni-
tored by GC-MS, and no 4a was observed.
7 W. Wang, F. Luo, S. Zhang and J. Cheng, J. Org. Chem.,
2010, 75, 2415.
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7122; (f) H. Li, P. Li, Q. Zhao and L. Wang, Chem.
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Acknowledgements
We thank the NSFC (no. 21372085) and GNSF (no.
10351064101000000) for financial support.
9 (a) F. Xiong, C. Qian, D. E. Lin, W. Zeng and X. X. Lu, Org.
Lett., 2013, 15, 5444; (b) H. Tang, C. Qian, D. E. Lin,
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Notes and references
1 For selected reviews on transition-metal catalyzed C–H
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Wiley-VCH, Weinheim, 2003.
2-(5-methoxy-biphenyl-2-ylazo)-phenol (4e) in 75% yield.
Possibly, the hydroxyl group is from H2O-containing aryl
acyl peroxide which was generally wetted with ca. 30%
H2O; (b) For the substrate 2e, no (4′-methoxy-biphenyl-
2-yl)-phenyl-diazene (4p) was observed possibly due to the
fact that the methoxyl group (MeO–) can stabilize the aryl
carboxyl radicals and retard the decarboxylation (see
ref. 10c).
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Paper
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