Palladium-catalyzed direct oxidative C-H cross-coupling of azoarenes with alcohols

Article abstract of DOI:10.1002/adsc.201300812

A palladium-catalyzed cascade oxidative C-H cross-coupling of azoarenes with alcohols was developed using tert-butyl hydroperoxide (TBHP) as oxidant. This reaction provides a convenient access to ortho-acylazoarenes under mild conditions in which readily available alcohols were used as the acyl sources.

Full text of DOI:10.1002/adsc.201300812

FULL PAPERS
DOI: 10.1002/adsc.201300812
À
Palladium-Catalyzed Direct Oxidative C H Cross-Coupling of
Azoarenes with Alcohols
Hui Tang,+a Cheng Qian,+a Dongen Lin,a,* Huanfeng Jiang,a and Wei Zenga,*
a
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, Peopleꢀs
Republic of China
E-mail: denlin@scut.edu.cn or zengwei@scut.edu.cn
+
These two authors contributed equally to this work.
Received: September 6, 2013; Revised: October 31, 2013; Published online: February 7, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300812.
Abstract: A palladium-catalyzed cascade oxidative which readily available alcohols were used as the
À
C H cross-coupling of azoarenes with alcohols was acyl sources.
developed using tert-butyl hydroperoxide (TBHP) as
oxidant. This reaction provides a convenient access Keywords: ortho-acylation; alcohols; azoarenes;
to ortho-acylazoarenes under mild conditions in cross-coupling; palladium
Introduction
the oxidation of the corresponding azo-containing
secondary alcohols,[16] and these methodologies suffer
À
Transition metal-catalyzed direct C H cross-coupling from harsh reaction conditions and a relatively limit-
reactions of two organic molecules are among the ed substrate scope. Therefore, developing a straightfor-
most attractive and challenging hot topics in organic ward and concise synthetic strategy to access azo-sub-
chemistry.[1] Recently, much attention has been partic- stituted aryl ketones therefore is still desirable. Re-
ularly focused on the regioselective cross-coupling via cently, Wang realized the Pd-catalyzed direct acyla-
À
C H bond activation with the chelation assistance of tion of azoarenes using prefunctionalized aldehydes
a directing group.[2] In the past decade, most elegant as the acyl sources.[17] Considering that stable and
work has demonstrated that various functional groups readily available alcohols could be converted into al-
containing heteroatoms, such as ketone,[3] nitrile,[4] dehydes by various oxidants including O2 and TBHP,
carboxylic acid,[5] alcohol,[6] triazoene,[7] pyridine,[8] etc.,[18] and also that the direct acylation of N-benzyl-
ester,[9] amide,[4b,10] aldehyde,[9a,11] imine,[12] or oxazo- triflamides, acetanilides and 2-arylpyridines with alco-
line[13] group, etc., could be used as an anchor to form hols in the presence of Pd(II)/oxidants reaction
cyclometalated intermediates, and the corresponding system has been successively reported, respectively,[19]
cyclometalated species would further react with elec- herein we describe a convenient Pd-catalyzed direct
À
À
trophiles or nucleophiles to realize versatile C H C H oxidative cross-coupling of azoarenes with non-
functionalizations. However, although significant prefunctionalized alcohols as ideal in situ generated
À
progress in C H cross-coupling has been achieved acylating agents to provide ortho-acylated azoarenes.
with the assistance of various directing groups, there
are only rare reported examples employing the azo
À
group as a directing group to accelerate the C H acti- Results and Discussion
vation/functionalization process.[14]
Azo-substituted aryl ketones are important struc- Azobenzene (1a) and benzoyl alcohol (2a) were first
tural motifs of photochemical materials and biosen- used as the model substrates to screen the reaction
sors. Moreover, these compounds could be easily con- conditions for the optimization of the catalyst, oxi-
verted into the corresponding amino or hydrazino dant, solvent, and temperature under an argon atmos-
products which are widely utilized in the field of or- phere (Table 1). We were pleased to find that when
ganic synthesis.[15] The present synthetic methods in- the mixture of azobezene (0.15 mmol) and benzoyl al-
volve the coupling of diazonium salts with arenes or cohol (0.15 mmol) was treated with 4.0 equiv. of
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Hui Tang et al.
Table 1. Optimization of the Pd-catalyzed ortho-acylation of
benzene being the best (entry 17). When the reaction
temperature was lowered to 808C, the yield could be
increased up to 81% (compare entries 17 with 18).
Further lowering the reaction temperature or chang-
ing the ratio of 1a/2a resulted in poorer yields (com-
pare entry 18 with entries 19 and 20) (see the Sup-
porting Information for more details).
azobenzene with toluene.[a]
With the optimized reaction conditions in hand, the
scope of this transformation was subsequently investi-
gated with regard to alcohols as the in situ generated
Entry Pd catalyst
Oxidant
Solvent
Yield [%][b]
À
acyl source. As shown in Table 2, the C H cross-cou-
1
2
PdCl2
Pd(TFA)2
TBHP
TBHP
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
37
34
35
trace
40
pling reaction of azobenzene with various alcohols
could proceed smoothly and furnish the correspond-
ing acylated products. A wide range of arylmethanols
with substituents on the benzene rings was investigat-
ed. The results demonstrated that the substitution on
the benzene ring showed significant electronic effects,
the substrates with a para or meta electron-withdraw-
ing group (such as 4-Cl, 4-F, 4-Br, 4-NO2, 3-NO2, 4-
CF3) on the phenyl ring afforded the desired products
in moderate to excellent yields (59–83%, 3-1f–3-1k).
On the contrary, a para or meta electron-donating
group-substituted benzyl alcohol (4-Me, 4-MeO, 3-
MeO) gave a low yield of the corresponding acylated
product (43–56%, 3-1b–3-1d), especially for the 4-hy-
U
3
4
PdCl
PdCl
N
TBHP
TBHP
TBHP
TBHP
DDQ
MnO2
Na2S2O8
O2
5
PdACHTUNGTRENNUNG(OAc)2
6
Pd(PPh3)4
U
30
0
7
–
8
9
Pd
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
G
trace
trace
trace
trace
trace
47
10
11
12
13
14
15
16
17
18
19
20
PhIACTHNGUETRNU(NG OAc)2 DCE
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TCE
CH3NO2 28
EtOAc
PhCF3
PhCl
PhCl
PhCl
PhCl
22
58
À
droxybenzyl alcohol, no C H cross-coupling reaction
68
81[c]
68[d]
68[e]
occurred, and azobenzene 1a was completely recov-
ered (3-1e). Moreover, we also extended the substrate
scope to heteroarylmethanols and aliphatic alcohols,
and obtained the desired acylated azoarenes (3-1l–3-
1o).
[a]
Unless otherwise noted, the reactions were carried out
using azobenzene (1a) (0.15 mmol) and phenylmethanol
(2a) (0.15 mmol) with palladium catalyst (10 mol%) in
the presence of oxidant (0.60 mmol, 4.0 equiv.) in solvent
(2.0 mL) at 1108C for 30 h under an argon atmosphere in
a sealed reaction tube, followed by flash chromatography
on SiO2.
Isolated yield.
Reaction temperature: 808C.
Reaction temperature: 608C.
1.5 equiv. of 2a were used.
The scope of the transformation with regard to
azoarenes was then explored with benzyl alcohol as
an acylating agent. The results from Table 3 showed
that no deleterious electronic effect of the para-sub-
stituted azoarene was found, and electronic-rich and
electronic-poor azoarenes gave the desired acylated
products in moderate to excellent yields (3-2a, 3-2b,
3-2d–3-2h). Yet, the ortho-substituted azobenzene
gave an inferior product yield to that of the para- or
meta-substituted azobezene due to steric hindrance
[b]
[c]
[d]
[e]
TBHP in DCE (2.0 mL) at 1108C for 30 h in the pres- (compare 3-2c with 3-2a and 3-2b). Moreover, we also
ence of various palladium catalysts (10 mol%) includ- investigated the electronic effect of various substitu-
ing PdCl2, Pd
N
ACHTUTGNERNNUG(PPh3)4, and PdACHTUGNTERN(NUGN OAc)2, etc. ents on the regioselectivity of the ortho-acylation of
(entries 1–6), PdACHTUNGTRENNUNG
desired product (3-1a) (entry 5). Notably, no desired tion reactions took place mainly on the electron-rich
1
3-1a was detected by TLC and H NMR methods in azo aromatic rings (compare 3-2i, 3-2k and 3-2m with
the absence of palladium salts even after 48 h 3-2j, 3-2l and 3-2n, respectively). Finally, we tried to
(entry 7). Encouraged by these positive results, we use 3-azopyridine as substrate, but no ortho-acylation
further investigated the effect of various oxidants on was observed under our reaction conditions (3-2o).
À
this transformation, and found that TBHP was the
We also ran the ortho-regioselective C H oxidative
most suitable oxidant, other oxidants such as DDQ, cross-coupling of azoarene 1a with (2-bromophenyl)-
MnO2 and Na2S2O8, etc., afforded poorer reactivities methanol 2p under our reaction conditions, and got
(compare entries 8–12 with entry 5). Subsequently, the acylated intermediate 3-2p in 60% yield
the effect of the solvent was also investigated (com- (Scheme 1). Then a subsequent Pd-catalyzed intramo-
pare entry 5 with entries 13–17), and TCE, DCE and lecular cyclocoupling reaction[20] of 3-2p could further
trifluorotoluene were the better solvents, with chloro- furnish the corresponding azofluorenone 4, which has
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Palladium-Catalyzed Direct Oxidative C H Cross-Coupling
Table 2. Scope of alcohols.[a,b]
[a]
All the reactions were carried out using azobenzene (1a) (0.15 mmol) and alcohol (2) (1.0 equiv.) with PdACHTUNGTRENNUNG(OAc)2
(10 mol%) in the presence of TBHP (4.0 equiv.) in PhCl (2.0 mL) at 808C for 30 h under an argon atmosphere in
a sealed reaction tube, followed by flash chromatography on SiO2.
Isolated yield.
[b]
potential use as a promising industrial dye or non-
linear optical device.[15d,f]
To further investigate the possible mechanism, the
mixture of phenylmethanol (1.0 mL)/PdACHTUNGTRENNUNG(OAc)2
(10 mol%)/TBHP (4.0 equiv.) in the absence of azo-
benzene was conducted and the reaction progress
monitored using GC-MS. After the reaction had been
carried out at 808C for 12 h, we could observe the for-
mation of benzaldehyde (58% GC yield) (Scheme 2,
a). We further ran the ortho-acylation of azobenzene
with benzaldehyde under our optimized reaction con-
ditions, and got a 75% yield of the ortho-acylated azo-
benzene 3-1a (Scheme 2, b). Moreover, we also ran
À
the Pd-catalyzed oxidative C H cross-coupling of
azobenzene (1a) with phenylmethanol (2a) in the
presence of TEMPO under the same reaction condi-
tions, and no desired 3-1a was observed (Scheme 2,
c). This control experiment indicated that a radical
process was possibly involved in this reaction system.
Scheme 1. Synthetic application of this transformation.
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Table 3. Scope of azoarenes.[a,b]
[a]
Unless otherwise noted, the reactions were carried out using azoarene (1) (0.15 mmol) and phenylmethanol (2)
(1.0 equiv.) with Pd(OAc)2 (10 mol%) in the presence of TBHP (4.0 equiv.) in PhCl (2.0 mL) at 808C for 30 h under an
AHCTUNGTRENNUNG
argon atmosphere in a sealed reaction tube, followed by flash chromatography on SiO2.
Isolated yield.
[b]
Based on the previously reported Pd-catalyzed sp2 a convenient route for the synthesis of ortho-acyl-
[17,21]
À
C H acylation,
and in combination with the re-
ACHTUNGTRENaNUGN zoarene derivatives. Further studies of the transition
À
sults from the above-mentioned control reactions, metal-catalyzed C H ortho-acylation of azoarenes
a possible mechanism for this transformation involves using alkanes as acyl sources are currently underway
the oxidation of alcohols to aldehydes under the reac- in our lab.
tion conditions, then the corresponding aldehydes are
further converted into acyl radicals which can afford
ortho-acylation products probably via a Pd(II)-cata-
lyzed C H activation process.
Experimental Section
[22,23]
À
General Information
Unless otherwise noted, all other commercially available re-
Conclusions
agents and solvents were used without further purification.
Purifications of reaction products were carried out by flash
In summary, we have developed a Pd (II)-catalyzed
chromatography using silica gel (40–63 mm). Infrared spec-
À
oxidative C H cross-coupling reaction of azoarenes
tra (IR) were recorded on an FT-IR spectrophotometer and
are reported as wavelength numbers (cmÀ1). Infrared spectra
were recorded by preparing a KBr pellet containing the title
with alcohols using TBHP as an oxidant. This proto-
col allows us to use simple and readily available alco-
hols as in situ generated acyl sources, and provides compound. 1H and 13C NMR spectra were recorded with tet-
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Palladium-Catalyzed Direct Oxidative C H Cross-Coupling
Scheme 2. Control reactions.
ramethylsilane (TMS) as internal standard at ambient tem-
perature unless otherwise indicated on a standard spectrom-
eter operating at 400 MHz for 1H and 100 MHz for 13C.
Chemical shifts are reported in parts per million (ppm) and
coupling constants are reported as Hertz (Hz). Splitting pat-
terns are designated as singlet (s), broad singlet (bs), dou-
blet (d), triplet (t). Splitting patterns that could not be inter-
preted or easily visualized are designated as multiplet (m).
Melting points were determined on a microscopic melting
point apparatus and are uncorrected. Low resolution mass
spectra were taken on an LC-MS instrument. High resolu-
tion mass spectra (HR-MS) were recorded on an IF-TOF
spectrometer (Micromass). All the azobenzene substrates
were prepared according to the previously reported proce-
dures.[24]
2360, 17887, 1754, 1664, 1595, 1454, 1389, 1282, 1232, 1177,
996, 840, 740, 682, 530, 475 cmÀ1.
(E)-[2-(Phenyldiazenyl)phenyl](para-tolyl)methanone (3-
1
1b):[25] Orange liquid; H NMR (400 MHz, CDCl3): d=7.89–
7.83 (m, 1H), 7.59 (t, J=5.9 Hz, 2H), 7.5–7.51 (m, 1H), 7.52
(d, J=1.2 Hz, 2H), 7.41 (ddd, J=8.2, 5.4, 3.0 Hz, 2H), 7.27
(qd, J=4.5, 1.0 Hz, 3H), 7.10 (d, J=8.0 Hz, 2H), 2.28 (s,
3H); 13C NMR (100 MHz, CDCl3): d=196.83, 152.11,
150.27, 143.65, 137.43, 135.94, 131.29, 130.81, 130.59, 129.67,
129.05, 128.89, 128.65, 122.95, 119.69, 21.66; MS (EI, 70 eV):
m/z= 300.13 (M+); IR (KBr): n=3829, 3744, 2923, 2854,
1661, 1602, 1461, 1286, 1150, 1025, 928, 835, 769, 687, 538,
472 cmÀ1.
(E)-(4-Methoxyphenyl)[2-(phenyldiazenyl)phenyl]metha-
1
none (3-1c):[25] Orange liquid; H NMR (400 MHz, CDCl3):
d=7.92 (d, J=7.8 Hz,1H), 7.76 (d, J=8.5 Hz, 2H), 7.65–
7.49 (m, 5H), 7.35 (q, J=4.4 Hz, 3H), 6.86 (d, J=8.5 Hz,
2H), 3.81 (s, 3H); 13C NMR (100 MHz, CDCl3): d=195.78,
163.39, 152.17, 150.16, 137.78, 131.92, 131.43, 131.28, 130.80,
130.43, 128.92, 128.52, 122.94, 119.34, 113.60, 55.45; MS (EI,
70 eV): m/z=316.12 (M+); IR (KBr): n=3779, 3712, 2943,
2824, 1761, 1702, 1501, 1234, 1202, 1017, 825, 785, 678, 558,
476 cmÀ1.
(E)-(3,5-Dimethoxyphenyl)[2-(phenyldiazenyl)phenyl]me-
thanone (3-1d):[25] Orange liquid; 1H NMR (400 MHz,
CDCl3): d=7.94 (d, J=7.8 Hz, 1H), 7.69–7.61 (m, 1H), 7.6–
7.51 (m, 4H), 7.40–7.33 (m, 3H), 6.91 (d, J=2.3 Hz, 2H),
6.57 (s, 1H), 3.75 (s, 6H); 13C NMR (100 MHz, CDCl3): d=
196.74, 160.66, 152.04, 150.45, 140.39, 136.65, 131.36, 130.75,
130.73, 128.93, 128.62, 122.96, 120.52, 107.33, 105.24, 55.58;
MS (EI, 70 eV): m/z= 346.04 (M+); IR (KBr): n=3729,
3446, 2360, 2341, 2026, 1603, 1384, 1130, 1110, 992, 669, 638,
616 cmÀ1.
General Procedure for the ortho-Acylation of
Azobenzenes
A sealed tube was charged with azo compound (0.15 mmol),
alcohol (0.15 mmol), PdACHTNUTRGNENG(U OAc)2 (0.015 mmol), TBHP
(0.60 mmol) and chlorobenzene (2.0 mL) under an argon at-
mosphere. The reaction vessel was placed in an oil bath.
After the mixture had been stirred at 808C for 30 h, it was
cooled to room temperature and concentrated under
vacuum. The corresponding crude product was purified by
flash chromatography (silica gel, ethyl acetate/petroleum
ether 1:20, v/v) to afford the desired acylated products.
(E)-Phenyl[2-(phenyldiazenyl)phenyl]methanone
(3-
1
1a):[25] Orange liquid; H NMR (400 MHz, CDCl3): d=7.94
(d, J=7.9 Hz, 1H), 7.77 (d, J=7.5 Hz, 2H), 7.67–7.62 (m,
1H), 7.58 (d, J=4.2 Hz, 2H), 7.50–7.42 (m, 3H), 7.39–7.30
(m, 5H); 13C NMR (100 MHz, CDCl3): d=197.14, 152.04,
150.38, 138.47, 136.92, 132.76, 131.35, 130.87, 130.82, 129.42,
128.90, 128.81, 128.34, 122.89, 120.06; MS (EI, 70 eV): m/z=
286.11 (M+); IR (KBr): n=3852, 3738, 3618, 2922, 2852,
(E)-(4-Fluorophenyl)[2-(phenyldiazenyl)phenyl]metha-
1
none (3-1f):[25] Orange liquid; H NMR (400 MHz, CDCl3):
d=7.98 (d, J=7.9 Hz, 1H), 7.86–7.79 (m, 2H), 7.64 (dtd, J=
17.0, 7.2, 1.7 Hz, 3H), 7.50 (dd, J=7.8, 1.5 Hz, 2H), 7.43–
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7.35 (m, 3H), 7.07 (t, J=8.6 Hz, 2H); 13C NMR (100 MHz,
CDCl3): d=195.55, 151.96, 150.28, 136.53, 134.85, 132.03,
131.94, 131.52, 130.94, 130.91, 128.98, 128.67, 122.85, 120.29,
115.60, 115.38; MS (EI, 70 eV): m/z=304.01 (M+); IR
(KBr): n=3790, 3492, 2921, 2850, 2360, 2341, 1786, 1738,
1710, 1480, 1450, 848, 762, 750, 577, 480 cmÀ1.
(E)-[2-(Phenyldiazenyl)phenyl](thiophen-3-yl)methanone
(3-1l): Orange liquid; H NMR (400 MHz, CDCl3): d=7.91
1
(d, J=7.9 Hz, 1H), 7.73 (s, 1H), 7.68–7.52 (m, 5H), 7.49 (d,
J=5.0 Hz, 1H), 7.37 (d, J=6.1 Hz, 3H), 7.25 (s, 1H);
13C NMR (100 MHz, CDCl3): d=190.55, 152.20, 150.19,
143.50, 137.84, 134.03, 131.40, 130.80, 130.75, 128.97, 128.45,
127.61, 126.16, 122.95, 119.56; HR-MS (ESI): m/z=
293.0731, calcd. for [M+H]+ C17H12N2OS: 293.0743; IR
(KBr): n=3264, 3061, 2956, 2821, 1814, 1673, 1550, 1445,
1300, 1094, 1068, 934, 867, 636, 612, 545, 507, 472 cmÀ1.
(E)-(4-Chlorophenyl)[2-(phenyldiazenyl)phenyl]metha-
1
none (3-1g):[25] Orange liquid; H NMR (400 MHz, CDCl3):
d=7.96 (d, J=8.0 Hz, 1H), 7.71 (d, J=8.5 Hz, 2H), 7.66
(td, J=7.8, 1.6 Hz, 1H), 7.57 (dt, J=7.4, 6.8 Hz, 2H), 7.46
(dd, J=7.8, 1.4 Hz, 2H), 7.36 (dd, J=15.8, 8.0 Hz, 5H);
13C NMR (100 MHz, CDCl3): d=195.86, 151.90, 150.32,
139.16, 136.85, 136.17, 131.58, 131.03, 130.98, 130.71, 129.00,
128.71, 128.69, 122.87, 120.56; MS (EI, 70 eV): m/z=320.07
(M+); IR (KBr): n=3063, 2925, 2855, 1669, 1587, 1481,
1398, 1290, 1150, 1092, 1031, 928, 844, 771, 683, 531,
475 cmÀ1.
(E)-(4-Bromophenyl)[2-(phenyldiazenyl)phenyl]metha-
none (3-1h):[25] Orange solid; mp 92–948C; 1H NMR
(400 MHz, CDCl3): d=7.96 (d, J=7.9 Hz, 1H), 7.65 (dd, J=
16.2, 7.9 Hz, 3H), 7.56 (dd, J=11.3, 7. Hz, 2H), 7.51 (d, J=
8.4 Hz, 2H), 7.46 (d, J=7.4 Hz, 2H), 7.37 (p, J=6.1 Hz,
3H); 13C NMR (100 MHz, CDCl3): d=151.90, 150.34,
137.28, 136.10, 131.67, 131.58, 131.05, 130.97, 130.82, 129.00,
128.72, 127.87, 122.87, 120.57; MS (EI, 70 eV): m/z=365.90
(M+H)+; IR (KBr): n=3061, 2924, 2853, 2362, 1914, 1669,
1480, 1432, 1302, 1068, 928, 875, 686, 642, 587, 530,
492 cmÀ1.
(E)-[2-(phenyldiazenyl)phenyl][4-(trifluoromethyl)phe-
nyl]methanone (3-1i): Orange liquid; 1H NMR (400 MHz,
CDCl3): d=8.01 (d, J=7.9 Hz, 1H), 7.89 (d, J=8.1 Hz, 2H),
7.77–7.70 (m, 1H), 7.65 (dd, J=5.0, 4.5 Hz, 4H), 7.40 (d, J=
7.1 Hz, 3H), 7.38–7.33 (m, 2H); 13C NMR (100 MHz,
CDCl3): d=196.00, 151.78, 150.46, 141.46, 135.53, 134.00,
131.69, 131.47, 131.08, 129.45, 129.00, 128.98, 125.41, 125.37,
122.79, 122.26, 120.85; HR-MS (ESI): m/z=355.1052, calcd.
for [M+H]+ C20H13F3N2O: 355.1053; IR (KBr): n=3727,
3623, 2924, 2853, 2360, 2341, 1672, 1325, 1310, 1260, 1129,
749, 687, 669 cmÀ1.
(E)-(4-Nitrophenyl)[2-(phenyldiazenyl)phenyl]methanone
(3-1j):[25] Orange solid; mp 75–778C; 1H NMR (400 MHz,
CDCl3): d=8.19 (d, J=8.8 Hz, 2H), 8.02 (d, J=7.6 Hz, 1H),
7.89 (d, J=8.9 Hz, 2H), 7.7–7.67 (m, 1H), 7.68–7.59 (m,
2H), 7.45–7.30 (m, 5H); 13C NMR (100 MHz, CDCl3): d=
195.21, 151.48, 150.51, 149.82, 143.27, 134.45, 131.96, 131.74,
131.25, 129.83, 129.09, 128.98, 123.64, 122.76, 122.14; MS
(EI, 70 eV): m/z=331.02 (M+); IR (KBr): n=3728, 3705,
2923, 2852, 2360, 2341, 1661, 1548, 1344, 750, 684, 669,
650 cmÀ1.
(E)-1-[2-(Phenyldiazenyl)phenyl]ethanone
(3-1m):[26]
1
Orange liquid; H NMR (400 MHz, CDCl3): d=7.94 (d, J=
7.7 Hz, 2H), 7.78 (d, J=7.9 Hz,1H), 7.68 (d, J=7.5 Hz,
1H), 7.62 (d, J=7.3 Hz, 1H), 7.56 (q, J=9.4 Hz, 5H), 2.65
(s, 3H); 13C NMR (100 MHz, CDCl3): d=202.63, 152.35,
150.34, 138.23, 131.74, 131.56, 130.75, 129.28, 128.25, 123.27,
118.53, 32.64; MS (EI, 70 eV): m/z=224.02 (M+); IR (KBr):
n=3469, 3062, 2923, 2851, 2360, 2341, 1959, 1765, 1642,
1423, 1357, 772, 745, 689, 657, 548, 438 cmÀ1.
(E)-1-[2-(Phenyldiazenyl)phenyl]propan-1-one (3-1n):[27]
1
Orange liquid; H NMR (400 MHz, CDCl3): d=7.89 (d, J=
8.1 Hz, 2H), 7.79 (d, J=7.5 Hz, 1H), 7.60–7.48 (m, 6H),
2.91 (q, J=7.3 Hz, 2H), 1.20 (t, J=7.3 Hz, 3H); 13C NMR
(100 MHz, CDCl3): d=206.30, 152.34, 150.01, 138.52, 131.64,
131.02, 130.80, 129.24, 127.94, 123.21, 119.04, 38.16, 8.48; MS
(EI, 70 eV): m/z=238.11 (M+); IR (KBr): n=3729, 3433,
2920, 2367, 2339, 1593, 1275, 1261, 1208, 750, 686, 503 cmÀ1.
(E)-1-[2-(Phenyldiazenyl)phenyl]butan-1-one
(3-1o):[25]
Orange liquid; 1H NMR (400 MHz, CDCl3): d=7.92–7.87
(m, 2H), 7.81–7.75 (m, 1H), 7.59–7.47 (m, 6H), 2.89 (t, J=
7.3 Hz, 2H), 1.81–1.67 (m, 2H), 0.94 (t, J=7.4 Hz, 3H);
13C NMR (100 MHz, CDCl3): d=205.81, 152.37, 150.01,
138.90, 131.63, 131.03, 130.79, 129.23, 127.94, 123.22, 118.56,
46.94, 17.92, 13.86; MS (EI, 70 eV): m/z= 252.04 (M+); IR
(KBr): n=3742, 3501, 3063, 2962, 2873, 2362, 1692, 1592,
1457, 1385, 1204, 1151, 1077, 992, 770, 686, 543 cmÀ1.
(E)-[5-Methyl-2-(para-tolyldiazenyl)phenyl]ACTHNUTRGNEUG(N phenyl)-
methanone (3-2a):[25] Orange liquid; 1H NMR (400 MHz,
CDCl3): d=7.85 (d, J=8.2 Hz, 1H), 7.76 (d, J=7.1 Hz, 2H),
7.44 (dd, J=14.9, 7.6 Hz, 2H), 7.39–7.28 (m, 5H), 7.10 (d,
J=8.1 Hz, 2H), 2.47 (s, 3H), 2.32 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=197.53, 150.18, 148.49, 141.69, 141.39,
138.61, 136.69, 132.61, 131.49, 129.53, 129.34, 129.16, 128.27,
122.75, 120.20, 21.45; MS (EI,70 eV): m/z=314.14 (M+); IR
(KBr): n=3472, 2921, 2853, 2361, 1663, 1593, 1448,
1277,1208, 1146, 961, 826, 744, 698, 644, 544 cmÀ1.
(E)-[4-Methyl-2-(meta-tolyldiazenyl)phenyl]ACTHNUTRGNEUG(N phenyl)-
methanone (3-2b): Orange liquid; 1H NMR (400 MHz,
CDCl3): d=7.76 (d, J=7.6 Hz, 2H), 7.70 (s, 1H), 7.52 (d,
J=7.7 Hz, 1H), 7.46 (t, J=7.3 Hz, 1H), 7.37 (dd, J=16.8,
9.0 Hz, 3H), 7.26–7.14 (m, 3H), 7.10 (s, 1H), 2.51 (s, 3H),
2.28 (s, 3H); 13C NMR (100 MHz, CDCl3): d=197.35,
152.28, 150.53, 141.52, 139.07, 138.74, 134.39, 132.50, 132.01,
131.52, 129.43, 129.08, 128.66, 128.24, 122.59, 120.87, 119.58,
21.49, 21.16; HR-MS (ESI): m/z=315.1519, calcd. for [M+
H]+ C21H18N2O: 315.1492; IR (KBr): n=3736, 3502, 3055,
2822, 2853, 1721, 1716, 1562, 1521,1471, 883, 825, 749, 702,
687, 660, 516, 452 cmÀ1.
(E)-(3-Nitrophenyl)[2-(phenyldiazenyl)phenyl]methanone
(3-1k): Orange solid; mp 128–1308C; 1H NMR (400 MHz,
CDCl3): d=8.57 (s, 1H), 8.30 (d, J=8.1 Hz, 1H), 8.04 (dd,
J=14.8, 7.9 Hz, 2H), 7.73 (t, J=7.5 Hz, 1H), 7.63 (dd, J=
19.8, 7.5 Hz, 2H), 7.55 (t, J=8.0 Hz, 1H), 7.43 (d, J=
7.7 Hz, 2H), 7.35 (dt, J=14.7, 6.5 Hz, 3H); 13C NMR
(100 Hz, CDCl3): d=194.65, 151.58, 150.51, 148.30, 140.03,
134.50, 134.47, 131.85, 131.70, 131.23, 129.56, 129.06, 128.93,
126.77, 123.73, 122.77, 121.94; HR-MS (ESI): m/z=
354.0847, calcd. for [M+Na]+ C19H13N3O3: 354.0849; IR
(KBr): n=3753, 3700, 2978, 2908, 2878, 2378, 2321, 1654,
1532, 1312, 780, 676, 652, 610 cmÀ1.
(E)-[3-Methyl-2-(ortho-tolyldiazenyl)phenyl]ACTHNUTRGNEUG(N phenyl)-
methanone (3-2c): Orange liquid, 1H NMR (400 MHz,
CDCl3): d=7.65 (d, J=7.6 Hz, 2H), 7.45 (dt, J=14.9,
7.5 Hz, 2H), 7.37 (t, J=7.3 Hz, 1H), 7.30 (d, J=8.1 Hz,
524
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FULL PAPERS
Palladium-Catalyzed Direct Oxidative C H Cross-Coupling
1H), 7.28–7.20 (m, 4H), 7.15 (d, J=7.5 Hz, 1H), 7.07 (t, J=
7.6 Hz, 1H), 2.76 (s, 3H), 2.27 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=196.58, 150.25, 150.12, 138.94, 138.09, 137.22,
132.52, 132.44, 131.33, 131.29, 131.15, 129.93, 129.01, 128.16,
126.49, 125.96, 115.64, 18.43, 17.28; HR-MS (ESI): m/z=
315.1486, calcd. for [M+H]+ C21H18N2O: 315.1492; IR
(KBr): n=3845, 3727, 3533, 2360, 2339, 1641, 1384, 1261,
1089, 749, 669, 493 cmÀ1.
431.1602; IR (KBr): n=2923, 2852, 1720, 1668, 1589, 1450,
1402, 1364, 1244, 1147, 1096, 1016, 856, 766, 687, 635 cmÀ1.
(E)-[5-Methoxy-2-(phenyldiazenyl)phenyl]ACTHNUTRGENUG(N phenyl)-
methanone (3-2i): Orange solid; mp 120–1228C; 1H NMR
(400 MHz, CDCl3): d=7.97 (d, J=8.9 Hz, 1H), 7.79 (d, J=
7.8 Hz, 2H), 7.48 (t, J=7.3 Hz, 1H), 7.42–7.33 (m, 4H), 7.29
(d, J=6.3 Hz, 3H), 7.14 (d, J=8.9 Hz, 1H), 7.05 (s, 1H),
3.92 (s, 3H); 13C NMR (100 MHz, CDCl3): d=196.91,
161.86, 152.06, 144.39, 138.88, 138.32, 132.78, 130.68, 129.34,
128.82, 128.34, 122.58, 122.16, 116.74, 112.93, 55.84; HR-MS
(ESI): m/z=317.1285, calcd. for [M+H]+ C20H16N2O2:
317.1285; IR (KBr): n=3059, 2923, 2849, 1663, 592, 1474,
1292,1240,1098, 1031,960, 891, 849, 815, 770, 691, 628, 553,
520 cmÀ1.
(E)-{5-Methoxy-2-[(4-methoxyphenyl)diazenyl]phenyl}-
ACHTUNGTRENNUNG
(phenyl)methanone (3-2d):[25] Orange liquid; 1H NMR
(400 MHz, CDCl3): d=7.93 (d, J=8.9 Hz, 1H), 7.78 (d, J=
7.5 Hz, 2H), 7.47 (t, J=7.3 Hz, 1H), 7.36 (t, J=7.8 Hz, 4H),
7.13 (dd, J=8.9, 2.7 Hz, 1H), 7.03 (d, J=2.7 Hz, 1H), 6.79
(d, J=8.9 Hz, 2H), 3.91 (s, 3H), 3.80 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=197.13, 161.81, 161.33, 146.44, 144.56,
138.43, 138.26, 133.62, 132.68, 130.16, 129.30, 128.47, 128.30,
124.43, 122.00, 116.77, 113.99, 112.88, 55.80, 55.48; MS (EI,
70 eV): m/z=346.13 (M+); IR (KBr): n=3723, 3397, 2921,
2851, 2363, 1745, 1712, 1699, 1652, 1574, 1473, 1419, 1316,
837, 749, 692, 515 cmÀ1.
(E)-{2-[(4-methoxyphenyl)diazenyl]phenyl}ACTHNUTRGNEUG(N phenyl)-
methanone (3-2j): Orange solid; mp 93–958C; 1H NMR
(400 MHz, CDCl3): d=7.91 (d, J=8.0 Hz, 1H), 7.76 (d, J=
7.5 Hz, 2H), 7.63 (t, J=7.1 Hz, 1H), 7.59–7.52 (m, 2H), 7.45
(dd, J=14.1, 8.1 Hz, 3H), 7.35 (t, J=7.6 Hz, 2H), 6.81 (d,
J=8.9 Hz, 2H), 3.81 (s, 3H); 13C NMR (100 MHz, CDCl3):
d=197.36, 162.35, 150.57, 146.48, 138.60, 136.45, 132.61,
130.77, 130.21, 129.36, 128.75, 128.27, 124.86, 120.02, 114.05,
55.52; HR-MS (ESI): m/z=317.1292, calcd. for [M+H]+
C20H16N2O2: 317.1285; IR (KBr): n=3735, 3433, 3062, 2921,
2849, 2360, 2339, 1734, 1663, 1597, 1581, 1314, 1285, 1252,
1141, 764, 623, 548, 515 cmÀ1.
(E)-{5-Fluoro-2-[(4-fluorophenyl)diazenyl]phenyl}-
ACHTUNGTRENNUNG
(phenyl)methanone (3-2e): Orange liquid; 1H NMR
(400 MHz, CDCl3): d=7.99 (dd, J=8.8, 5.1 Hz, 1H), 7.79
(d, J=7.8 Hz, 2H), 7.54 (t, J=7.4 Hz, 1H), 7.49–7.26 (m,
6H), 7.03 (t, J=8.6 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d=195.47, 165.15, 163.29, 162.62, 148.42, 146.54, 139.22,
139.15, 137.85, 133.14, 129.37, 128.49, 124.96, 124.87, 122.11,
122.02, 117.98, 117.75, 116.08, 115.88, 115.85, 115.64; HR-
MS (ESI): m/z=323.0996, calcd. for [M+H]+ C19H12F2N2O:
323.0991; IR (KBr): n=3072, 2924, 1730, 1656, 1592, 1491,
1309, 1274, 1226, 1128, 1083, 843, 749, 701, 638, 551 cmÀ1.
(E)-{5-Chloro-2-[(4-chlorophenyl)diazenyl]phenyl}-
(E)-[5-methoxy-2-(para-tolyldiazenyl)phenyl]ACHTUGNTERN(UNNG phenyl)-
1
methanone (3-2k): Orange solid; mp 108–1108C; H NMR
(400 MHz, CDCl3): d=7.95 (d, J=8.9 Hz, 1H), 7.78 (d, J=
7.3 Hz, 2H), 7.46 (t, J=7.4 Hz, 1H), 7.36 (t, J=7.6 Hz, 2H),
7.28 (d, J=8.2 Hz, 2H), 7.15–7.02 (m, 4H), 3.90 (s, 3H),
2.31 (s, 3H); 13C NMR (100 MHz, CDCl3): d=197.01,
161.63, 150.19, 144.47, 141.26, 138.63, 138.40, 132.72, 129.50,
129.32, 128.31, 122.57, 122.07, 116.74, 112.92, 55.82, 21.41;
HR-MS (ESI): m/z=331.1456, calcd. for [M+H]+
C21H18N2O2: 331.1441; IR (KBr): n=2921, 2851, 2361, 2339,
1665, 1594, 1449, 1416, 1314, 1284, 1234, 1177, 1149, 1101,
1030, 962, 828, 749, 700, 553, 507 cmÀ1.
ACHTUNGTRENNUNG
(phenyl)methanone (3-2f):[25] Orange solid; mp 121–1228C;
1H NMR (400 MHz, CDCl3): d=7.81 (d, J=8.6 Hz, 1H),
7.68 (d, J=7.8 Hz, 2H), 7.56–7.47 (m, 2H), 7.43 (t, J=
7.3 Hz, 1H), 7.30 (dd, J=17.1, 8.4 Hz, 4H), 7.24–7.16 (m,
2H); 13C NMR (100 MHz, CDCl3): d=195.37, 150.26,
148.42, 138.53, 137.88, 137.70, 137.39, 133.20, 130.98, 129.39,
129.28, 128.81, 128.52, 124.17, 121.12; MS (EI, 70 eV): m/z=
354.03 (M+); IR (KBr): n=3062, 2923, 1661, 1583, 1474,
1397, 1267, 1146, 1081, 853, 905, 830, 801, 702, 642,
539 cmÀ1.
(E)-{2-[(4-Methoxyphenyl)diazenyl]-5-methylphenyl}-
AHCTUNGTREG(NNUN phenyl)methanone (3-2l): Orange solid; mp 94–968C;
1H NMR (400 MHz, CDCl3): d=7.83 (d, J=8.2 Hz,1H),
7.78–7.74 (m, 2H), 7.51–7.31 (m, 7H), 6.80 (d, J=9.0 Hz,
2H), 3.80 (s, 3H), 2.47 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=197.58, 162.10, 148.59, 146.47, 140.93, 138.67,
136.43, 132.54, 131.45, 129.32, 129.12, 128.24, 124.66, 120.16,
114.00, 55.49, 21.40; HR-MS (ESI): m/z=331.1450, calcd.
for [M+H]+ C21H18N2O2: 331.1441; IR (KBr): n=2919,
2849, 2361, 2338, 1659, 1596, 1499, 1443, 1384, 1249, 1209,
1175, 1140, 1101, 836, 694, 501 cmÀ1.
(E)-{5-Bromo-2-[(4-bromophenyl)diazenyl]phenyl}-
ACHTUNGTRENNUNG(phenyl)methanone (3-2g): Orange solid; mp 158–1598C;
1H NMR (400 MHz, CDCl3): d=7.82 (d, J=8.6 Hz, 1H),
7.79–7.71 (m, 4H), 7.51 (t, J=7.3 Hz, 1H), 7.46 (d, J=
8.5 Hz, 2H), 7.39 (t, J=7.6 Hz, 2H), 7.28 (d, J=8.5 Hz,
2H); 13C NMR (100 MHz, CDCl3): d=195.20, 150.64,
148.81, 138.68, 137.89, 133.97, 133.20, 132.28, 131.73, 129.38,
128.51, 126.29, 125.73, 124.37, 121.21; HR-MS (ESI): m/z=
464.9203, calcd. for [M+Na]+ C19H12Br2N2O: 464.9209; IR
(KBr): n=3433, 2360, 2340, 1660, 1275, 1261, 750, 483 cmÀ1.
(E)-Ethyl 3-benzoyl-4-{[4-(ethoxycarbonyl)phenyl]diazen-
(E)-Ethyl 4-[(2-benzoylphenyl)diazenyl]benzoate (3-2m):
1
Orange solid; mp 113–1158C; H NMR (400 MHz, CDCl3):
d=8.00 (d, J=8.5 Hz, 2H), 7.96 (d, J=8.2 Hz, 1H), 7.81–
7.73 (m, 2H), 7.71–7.60 (m, 3H), 7.53–7.42 (m, 3H), 7.38 (t,
J=7.6 Hz, 2H), 4.37 (q, J=7.1 Hz, 2H), 1.39 (t, J=
7.1 Hz,3H); 13C NMR (100 MHz, CDCl3): d=196.96, 165.90,
154.40, 150.21, 138.42, 137.36, 132.91, 132.44, 131.58, 130.92,
130.36, 129.39, 128.97, 128.41, 122.60,119.89, 61.27, 14.29;
HR-MS (ESI): m/z=359.1395, calcd. for [M+H]+
C22H18N2O3: 359.1390; IR (KBr): n=2920, 2850, 1868, 1792,
1772, 1748, 1714, 1447, 1401, 1364, 1271, 860, 752, 697, 631,
544 cmÀ1.
1
yl}benzoate (3-2h): Orange solid: mp 122–1238C; H NMR
(400 MHz, CDCl3): d=8.37–8.26 (m, 2H), 8.00 (dd, J=13.0,
8.4 Hz, 3H), 7.76 (d, J=7.4 Hz, 2H), 7.50 (dd, J=16.1,
8.0 Hz, 3H), 7.40 (t, J=7.7 Hz, 2H), 4.41 (dq, J=24.6,
7.1 Hz, 4H), 1.41 (dt, J=14.1, 7.1 Hz, 6H); 13C NMR
(100 MHz, CDCl3): d=195.95, 165.77, 165.24, 154.33, 152.53,
137.99, 137.29, 133.19, 133.01, 132.88, 132.04, 130.43, 130.29,
129.46, 128.53, 122.85, 119.75, 61.68, 61.35, 14.28; HR-MS
(ESI): m/z=431.1601, calcd. for [M+H]+ C25H22N2O5:
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FULL PAPERS
Hui Tang et al.
(E)-Ethyl 3-benzoyl-4-(phenyldiazenyl)benzoate (3-2n): References
1
Orange liquid; H NMR (400 MHz, CDCl3): d=8.34 (d, J=
8.4 Hz, 1H), 8.29 (s, 1H), 8.00 (d, J=8.4 Hz, 1H), 7.80 (d,
J=7.6 Hz, 2H), 7.52 (dd, J=14.0, 7.2 Hz, 3H), 7.47–7.32 (m,
5H), 4.45 (q, J=7.1 Hz, 2H), 1.45 (t, J=7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3): d=196.14, 165.37, 152.78,
152.06, 138.04, 136.86, 133.03, 132.27, 132.01, 131.96, 130.16,
129.48, 129.00, 128.45, 123.16, 119.92, 61.58, 14.30; HR-MS
(ESI): m/z=359.1410, calcd. for [M+H]+ C22H18N2O3:
359.1390; IR (KBr): n=2931, 2876, 1968, 1893, 1768, 1732,
1711, 1523, 1412, 1401, 1365, 1257, 980, 860, 688, 577, 523,
497 cmÀ1.
(E)-(2-Bromophenyl)[2-(phenyldiazenyl)phenyl]metha-
none (3-2p): Orange liquid; 1H NMR (400 MHz, CDCl3):
d=8.57 (s, 1H), 8.30 (d, J=8.1 Hz, 1H), 8.04 (dd, J=14.8,
7.9 Hz, 2H), 7.73 (t, J=7.5 Hz, 1H), 7.69–7.59 (m, 2H), 7.55
(t, J=8.0 Hz, 1H), 7.43 (d, J=7.7 Hz, 2H), 7.35 (dt, J=14.7,
6.5 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=194.65,
151.58, 150.51, 148.30, 140.03, 134.50, 134.47, 131.85, 131.70,
131.23, 129.56, 129.06, 128.93, 126.77, 123.73, 122.77, 121.94;
HR-MS (ESI): m/z=365.0297, calcd. for [M+H]+
C19H13BrN2O: 365.0284; IR (KBr): n=3021, 2918, 2868,
1978, 1673, 1504, 1478, 1313, 1043, 845, 634, 577, 534,
497 cmÀ1.
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À
[2] For selected reviews on transition metal-catalyzed C H
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2010, 110, 1082; c) G. Song, F. Wang, X. Li, Chem. Soc.
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[3] Selected examples: a) F. W. Patureau, T. Besset, F. Glo-
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Shi, J. Q. Yu, Science 2010, 327, 315; b) B. F. Shi, Y. H.
Zhang, J. K. Lam, D. H. Wang, J. Q. Yu, J. Am. Chem.
Soc. 2010, 132, 460.
[6] Selected examples: a) M. Mewald, J. A. Schiffner, M.
Oestreich, Angew. Chem. 2012, 124, 1797; Angew.
Chem. Int. Ed. 2012, 51, 1763; b) Y. Lu, D. H. Wang,
K. M. Engle, J. Q. Yu, J. Am. Chem. Soc. 2010, 132,
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Am. Chem. Soc. 2011, 133, 12406.
Synthesis of (E)-1-(Phenyldiazenyl)-9H-fluoren-9-one
(4)
[7] C. Wang, H. Chen, Z. Wang, J. Chen, Y. Huang,
Angew. Chem. 2012, 124, 7354; Angew. Chem. Int. Ed.
2012, 51, 7242.
Anhydrous KOAc (19.6 mg, 0.20 mmol), DavePhos (4 mg,
0.01 mmol) and K2CO3 (27.6 mg, 0.20 mmol) were succes-
sively added to a solution of PdACHTUNTRGNEUNG(PPh3)4 (11.5 mg, 0.01 mmol)
[8] Selected examples: a) Y. Li, B. J. Li, W. H. Wang, W. P.
Huang, X. S. Zhang, K. Cheng, Z. J. Shi, Angew. Chem.
2011, 123, 2163; Angew. Chem. Int. Ed. 2011, 50, 2115;
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Soc. 2010, 132, 10272; d) A. Garcia-Rubia, M. A. Fer-
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Eur. J. 2011, 17, 3567; e) A. Garcia-Rubia, B. Urone,
R. G. Arrays, J. C. Carretero, Angew. Chem. 2011, 123,
11119; Angew. Chem. Int. Ed. 2011, 50, 10927; f) X.
Wang, L. Truesdale, J. Q. Yu, J. Am. Chem. Soc. 2010,
132, 3648.
[9] Selected examples: a) T. Besset, N. Kuhl, F. W. Patur-
eau, F. Glorius, Chem. Eur. J. 2011, 17, 7167; b) S. H.
Park, J. Y. Kim, S. Chang, Org. Lett. 2011, 13, 2372.
[10] Selected examples: a) H. X. Dai, A. F. Stepan, M. S.
Plummer, Y. H. Zhang, J. Q. Yu, J. Am. Chem. Soc.
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in DMA (1.5 mL) and the resulting suspension was stirred
at room temperature for 15 min, then a solution of the cor-
responding acylated intermediate 3-2p (36.4 mg, 0.10 mmol)
in DMA (0.5 mL) was introduced. The system was heated at
1108C for 24 h. Then, the solvent was removed under
vacuum, and the corresponding residue was purified by flash
chromatography on silica gel (eluent: petroleum ether/ethyl
acetate=100:1) to afford 4 as an orange liquid; yield: 35%.
1H NMR (400 MHz, CDCl3): d=8.06 (d, J=7.2 Hz, 2H),
7.70 (d, J=7.3 Hz, 1H), 7.64–7.49 (m, 7H), 7.44 (d, J=
7.9 Hz, 1H), 7.34 (t, J=7.3 Hz, 1H); 13C NMR (100 MHz,
CDCl3): d=192.31, 153.01, 150.56, 145.54, 143.78, 135.18,
134.55, 134.38, 131.90, 129.51, 129.22, 128.21, 124.30, 123.62,
121.56, 120.36, 116.91; HR-MS (ESI): m/z=285.1037, calcd.
for [M+H]+ C19H12N2O: 285.1022; IR (KBr): n=3861, 3742,
3649, 3620, 2361, 1741, 1707, 1646, 1515, 1378, 1250, 1143,
759, 678, 520 cmÀ1.
Acknowledgements
The authors thank the NCET (No. 10-0371), NSFC (No.
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