Palladium-catalyzed highly selective ortho-halogenation (I, Br, Cl) of arylnitriles via sp2 C-H bond activation using cyano as directing group

Article abstract of DOI:10.1021/jo302765g

A palladium-catalyzed ortho-halogenation (I, Br, Cl) of arylnitrile is described. The optimal reaction conditions were identified after examining various factors such as catalyst, additive, solvent, and reaction temperature. Using cyano as the directing group, the halogenation reaction gave good to excellent yields. The method is compatible to the arylnitriles with either electron-withdrawing or electron-donating groups. The reaction is available to the substrate in at least gram scale. The present method was successfully applied to the synthesis of the precursors of paucifloral F and isopaucifloral F.

Full text of DOI:10.1021/jo302765g

Note
pubs.acs.org/joc
Palladium-Catalyzed Highly Selective ortho-Halogenation (I, Br, Cl) of
Arylnitriles via sp2 C−H Bond Activation Using Cyano as Directing
Group
Bingnan Du,† Xiaoqing Jiang,† and Peipei Sun*,†,‡
‡
†Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Materials Science and Key Laboratory of Applied
Photochemistry, Nanjing Normal University, Nanjing 210097, China
S
* Supporting Information
ABSTRACT: A palladium-catalyzed ortho-halogenation (I, Br, Cl) of
arylnitrile is described. The optimal reaction conditions were identified
after examining various factors such as catalyst, additive, solvent, and
reaction temperature. Using cyano as the directing group, the
halogenation reaction gave good to excellent yields. The method is
compatible to the arylnitriles with either electron-withdrawing or
electron-donating groups. The reaction is available to the substrate in
at least gram scale. The present method was successfully applied to the
synthesis of the precursors of paucifloral F and isopaucifloral F.
ver the past decade, transition-metal-catalyzed C−H
Suzuki coupling, Negishi coupling, Heck coupling, et al).9
Consequently, efficient and selective methods to access this
class of compounds are highly valuable. Several groups reported
palladium-catalyzed sp2 C−H halogenations directed by
heteroaromatics or other electron-donating directing groups,10
but direct iodination to the aromatic ring was still rare because
of the highly oxidative addition activity of aryl iodides to
transition metals. Also, some methods were unavailable to the
electron-deficient substrates. To develop new method enabling
the high-yielding and selective formation of valuable and
versatile C−X (X = I, Br, Cl) bonds, compatible with a large
scope of diverse arenes, is of prime synthetic value. Since the
cyano is an electron-withdrawing (type II) group, the general
electrophilic aromatic substitution to arylnitriles cannot give
ortho-halogenated arylnitriles. The cyclometalation-based ortho-
C−H activation will provide the possibility for the direct ortho-
halogenation. In this work, we wish to report an efficient
method for the synthesis of o-haloarylnitriles via a Pd-catalyzed,
cyano-directed halogenation of aromatic C−H bond using NXS
(X = I, Br, Cl) as halogenation reagents. As an important
polyfunctional reagent, one of the products was further
successfully used to synthesize a precursor of a natural
compound.
O
functionalization has emerged as a valuable and atom-
economical strategy for organic synthesis. Of particular interest
is the palladium-catalyzed chelation-directed sp2 C−H
activation, which provides various valuable products in a highly
efficient way.1 Utilizing substrates with weakly coordinating
directing groups enables unprecedented breadth in the
functionalization step, owing to the higher reactivity of the
putative cyclopalladated intermediates, which is becoming a
powerful approach for developing synthetically versatile
reactions.2 Thus, some weakly coordinating directing groups
such as carboxyl,3 hydroxyl,4 and carbonyl5 have been adopted
in the cyclometalation in recent years. It is well-known that the
cyano group is not only a coordinating functional group but
also an important precursor for a multitude of transformations
into various functional groups such as carboxylic acids, esters,
amides, amines, aldehydes, tetrazoles, and ketones.6 In our
previous works, palladium-catalyzed cyano-directed sp2 C−C
and C−O bond formation reactions were studied.7 We believe
that expanding the cyano-directed C−H functionalization
should be significant in the synthesis of polyfunctional nitriles
and the related compounds.
Though a plethora of carbon−carbon bond-formation
reactions have been discovered by the transition-metal-
catalyzed C−H functionalization, application of this strategy
to create carbon−heteroatom bonds, in particular carbon−
halogen bonds, is still underdeveloped. Aryl halides are
extremely valuable starting materials for synthetic elaboration.
For example, they are used as precursors for the synthesis of
organometallic reagents and for nucleophilic substitution
reactions.8 In recent decades, aryl halides, especially aryl
iodides and aryl bromides, have also found widespread utility as
substrates to construct complex structures in organic syntheses
via transition-metal-catalyzed coupling reactions (such as
The reaction of benzonitrile and N-iodosuccinimide (NIS)
was initially selected to optimize the reaction conditions.
Without catalyst, the reaction did not take place at all.
Pd(OAc)2 seemed to be the efficient catalyst for this
transformation to give the only ortho-iodinated product, 2-
iodo-benzonitrile, while other palladium species such as
Pd(TFA)2, PdCl2, Pd(acac)2, and Pd(PPh3)4 were substantially
less effective (entries 7−10, Table 1). A 5 mol % catalyst
Received: December 20, 2012
© XXXX American Chemical Society
A
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Note
a
14−18), while in DCE the highest yield was obtained (entry 4).
At 70 °C, the reaction proceeded smoothly and finished in 12
h. Decreasing the temperature to 50 °C led to a lower yield of
72% (entry 19). Besides, I2 was also tested as iodic source.
However, a mixture with a low yield was obtained under above
reaction conditions.
Table 1. Optimization of the ortho-Halogenation Reaction
b
entry
catalyst
additive (equiv)
solvent
DCE
yield (%)
To test the scope of this ortho-iodination reaction, we
explored variously substituted arylnitriles under the established
reaction conditions (Table 2). For most of the substrates we
employed, the reaction gave the corresponding products with
high selectivity and good yields. It seemed that the substrates
with different substitution patterns on the aryl ring had no
evident effect on this transformation. For example, the reactions
proceeded smoothly with similar yields when methyl, methoxyl,
and nitro groups existed, respectively, on the substrates. The
presence of a methyl group in the ortho-position of the cyano
group did not bring decrease of the yield by “ortho-substituent
effect”, which generally existed in many palladium-catalyzed
coupling reactions (2b). An interesting regioselectivity could be
found in that when a meta-substituent existed at arylnitrile, the
iodination did not take place between cyano and that
substituent because of the steric hindrance. It is worth noting
that in the presence of nitro, a strongly electron-withdrawing
group, the reaction still gave a yield of 79% (2f). Moreover,
with 1-naphthonitrile, an iodination product on the 8-position
was obtained with moderate yield (2k) and no 2-position
iodination product was found, which may be because a more
stable cyclopalladated intermediate could be generated on 8-
position. Several disubstituted benzonitrile derivatives were also
tested, and high yields were achieved (2i, 2j).
1
2
3
4
PTSA (0.5)
PTSA (0)
0
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(TFA)2
PdCl2
DCE
22
PTSA (1)
DCE
80
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PivOH (0.5)
CF3COOH (0.5)
CH3COOH (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
PTSA (0.5)
DCE
84
c
5
d
DCE
85
6
DCE
70
7
DCE
56
8
DCE
trace
trace
trace
58
9
Pd(acac)2
Pd(PPh3)4
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
DCE
10
11
12
13
14
15
16
17
18
DCE
DCE
DCE
63
DCE
32
toluene
dioxane
DMF
CH3COOH
CH3CN
DCE
43
35
55
38
10
e
19
72
a
Reaction conditions: unless otherwise specified, all reactions were
carried out with benzonitrile (0.5 mmol), NIS (0.55 mmol), catalyst (5
mol %), and additive (0.5 equiv) in 2.0 mL of solvent under air
atmosphere at 70 °C for 12 h. Isolated yields. 10 mol % catalyst was
used. 3 mol % catalyst was used. The reaction performed at 50 °C.
b
c
d
e
We next examined the bromination and chlorination of
arylnitriles under the same reaction conditions (Table 3).
Similar to the iodination described above, for the most of the
substrates we used the reaction gave good yields. Good
tolerances to the chemically active functional groups were also
revealed. For example, the bromo and ester groups on
arylnitriles remained after this palladium-catalyzed reaction
(3g, 3m, 4m, 5m, 3n). It is worth noting that when 1.1 equiv of
NXS was added to the reaction system, only monohalogenation
reaction took place, but the presence of excess halogenation
loading gave a high yield of 84%. Increasing the amount of
Pd(OAc)2 to 10 mol % did not bring an evident improvement
of the yield, while decreasing the catalyst to 3 mol % lowered
the yield to 70% (entries 5, 6). An acidic additive was proved to
be essential to this reaction. Some reagents such as p-
toluenesulfonic acid (PTSA), PivOH, CF3COOH, and
CH3COOH were tested in which PTSA gave the best result
(entries 11−13). Another factor to influence this reaction was
the solvent. In toluene, dioxane, DMF, CH3COOH, and
CH3CN, the reaction gave poor to moderate yields (entries
a
Table 2. ortho-Iodination of Arylnitriles
a
All reactions were carried out with arylnitrile (0.5 mmol), NIS (0.55 mmol), catalyst (5 mol %), and PTSA (0.5 equiv) in 2.0 mL of DCE under air
b
atmosphere at 70 °C for 12 h. Isolated yields.
B
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Note
a
Table 3. ortho-Bromination and Chlorination of Arylnitriles
a
All reactions were carried out with arylnitrile (0.5 mmol), NXS (0.55 mmol, X = Br, Cl), catalyst (5 mol %), and PTSA (0.5 equiv) in 2.0 mL of
b
c
DCE under air atmosphere at 70 °C for 12 h. Isolated yields. 4-Bromobenzonitrile was used as reactant, and 2.5 equiv of NCS was added.
Scheme 1. Synthesis of Precursors of Paucifloral F and Isopaucifloral F
reagent could give a dihalogenation product with a moderate
yield (5m).
Up to now, the application of transition-metal-catalyzed C−
H functionalization in the syntheses of complex organic
molecules has remained a formidable challenge to chemists.
Reacting scale is a key restraining factor in the use of many
methods in organic synthesis. In this context, expanding
reacting weight exhibits particular interest, so we attempted to
conduct the reaction on gram scale. Use 20 mmol (2.34 g) of 3-
methylbenzonitrile as the reactant, under the established
iodination reaction conditions, 3.78 g (yield 78%) of 2-iodo-
5-methylbenzonitrile was obtained. Similarly, the bromination
C
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Note
of 20 mmol (2.34 g) of 4-methylbenzonitrile gave 3.15 g (yield
81%) of 2-bromo-4-methylbenzonitrile. That is to say,
decreases of less than 12% of the yields were revealed when
the reaction proceeded on the gram scale, which demonstrates
the possibility to use this method in general organic synthesis.
We next decided to use this convenient halogenation in the
synthesis of the precursors of natural products paucifloral F and
its regioisomer isopaucifloral F, both of them compounds with
anticancer activity.11 First, 3, 5-dimethoxybenzonitrile (1i)
reacted with NIS to give ortho-iodinated product 2-iodo-3,5-
dimethoxybenzonitrile (2i) with an isolated yield of 88%
(Scheme 1). Catalyzed by Pd(dba)2, the reaction of 2i with
compound 6, which was obtained through a Sonogashira
reaction, generated the products 7a and 7b,12 which could be
isolated easily by column chromatography and gave yields of
30% and 43%, respectively.
established method is further expected to be used in the
syntheses of many types of complex organic compounds and
natural products.
EXPERIMENTAL SECTION
■
General. All reactions were run in a sealed tube with a Teflon-lined
cap under air atmosphere. All reagents were commercially available
1
and were used without purification. H NMR and 13C NMR spectra
were recorded in CDCl3 [using (CH3)4Si (for 1H, δ = 0.00; for 13C, δ
= 77.00) as internal standard]. The following abbreviations are used to
designate the multiplicities: s = singlet, d = doublet, t = triplet, q =
quartet, m = multiplet. Melting points are uncorrected. HRMS was
obtained by ESI on TOF mass analyzer.
General Procedures for the Palladium-Catalyzed Halogen-
ation of Arylnitriles. Arylnitrile (0.5 mmol), NXS (0.55 mmol),
Pd(OAc)2 (0.025 mmol), PTSA (0.25 mmol), and DCE (2.0 mL)
were added into a 25-mL sealed tube with a Teflon-lined cap. The
mixture was heated at 70 °C (oil bath temperature) for 12 h. After
cooling to room temperature, the volatiles were removed under
reduced pressure, and the residue was purified by a flash column
chromatography on silica gel using EtOAc/hexane (1:5) as eluent to
give the corresponding product.
A possible mechanism was proposed to account for this
palladium-catalyzed regioselective halogenation reaction
(Scheme 2). First, the coordination of cyano in arylnitrile to
Scheme 2. Plausible Reaction Mechanism
Preparation of 1,3-Dimethoxy-5-((4-methoxyphenyl)-
ethynyl)benzene (6). 3,5-Dimethoxyiodobenzene (264 mg, 1.0
mmol), Pd(PPh3)2Cl2 (35 mg, 0.05 mmol), CuI (19 mg, 0.1 mmol),
and 4-methoxyphenylacetylene (185 mg, 1.4 mmol) were added into
Et3N (8 mL). The solution was stirred under N2 at room temperature
for 18 h. After purification by column chromatography, 1,3-dimethoxy-
5-((4-methoxyphenyl)ethynyl)benzene (6) was obtained as a colorless
oil in 83% yield.
Synthesis of Indenones (7a and 7b). 2-Iodo-3,5-dimethox-
ybenzonitrile (2i) (72 mg, 0.25 mmol), Pd(dba)2 (14.4 mg, 0.025
mmol), Et3N (25.3 mg, 0.25 mmol), and compound (6) (198 mg, 0.75
mmol) were added into a 9:1 DMF/water solution (5 mL). The
reaction mixture was stirred at 130 °C for 24 h. After purification by
column chromatography on silica gel (60, academic grade) using
CH2Cl2/hexane (1:2) as eluent, indenone (7a and 7b) were obtained
as purple solids in 30% and 43% yields, respectively.
1
2-Iodobenzonitrile (2a). Yield 96 mg, 84%. H NMR (400 MHz,
CDCl3) δ 7.93 (d, J = 8.0 Hz, 1H), 7.62 (d, J = 8.0 Hz, 1H), 7.48 (t, J
= 7.9 Hz, 1H), 7.28−7.33 (m, 1H); 13C NMR (100 MHz, CDCl3) δ
139.6, 134.3, 133.7, 128.3, 120.6, 119.3, 98.4.
1
2-Iodo-6-methyl-benzonitrile (2b). Yield 101 mg, 83%. H NMR
(400 MHz, CDCl3) δ 7.74 (d, J = 7.9 Hz, 1H), 7.30 (d, J = 8.0 Hz,
1H), 7.17 (t, J = 7.9 Hz, 1H), 2.60 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 144.7, 136.8, 133.3, 129.5, 120.9, 118.6, 98.8, 21.6.
Pd(OAc)2 formed a cyclopalladated intermediate A in which
the cyano group coordinated with palladium using its π-
electrons between carbon and nitrogen. This was different from
the n-electron coordination in some other coordinating group
directed C−H bond activation, and the weak coordination
property of this cyclopalladated intermediate might make it
have higher reactivity. Acetate then presumably participated in
aromatic proton abstraction to generate an aryl palladium
intermediate B, followed by an oxidative addition of NXS to
intermediate B to form intermediate C.10b,c The function of
PTSA in this reaction system is presumably to protonate the
carbonyl group of N-halosuccinimide (NXS) and make it a
more effective X+ source.10l The subsequent reductive
elimination of C gave the ortho-halogenated product and
regenerated the PdII catalyst.
In summary, a practical strategy for the ortho-halogenation of
arylnitriles was developed by a simple palladium-catalyzed
reaction with regioselectivities and high yields. It is applicable
to iodination, bromination, and chlorination and allows the use
of substrates with electron-withdrawing or electron-donating
groups. Moreover, the reaction is available to at least the gram
scale. As an example, it was successfully applied to the synthesis
of the precursors of paucifloral F and isopaucifloral F. The
1
2-Iodo-5-methyl-benzonitrile (2c). Yield 108 mg, 89%. H NMR
(400 MHz, CDCl3) δ 7.78 (d, J = 8.2 Hz, 1H), 7.42 (s, 1H), 7.12 (d, J
= 8.0 Hz, 1H), 2.35 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 139.3,
138.8, 134.9, 134.8, 120.4, 119.4, 94.2, 20.8.
1
2-Iodo-4-methyl-benzonitrile (2d). Yield 104 mg, 87%. H NMR
(400 MHz, CDCl3) δ 7.75 (s, 1H), 7.47 (d, J = 7.9 Hz, 1H), 7.25 (d, J
= 7.9 Hz, 1H), 2.38 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 145.1,
140.1, 133.9, 129.2, 119.6, 117.1, 98.3, 21.4.
1
2-Iodo-4-methoxybenzonitrile (2e). Yield 113 mg, 86%. H NMR
(400 MHz, CDCl3) δ 8.05 (s, 1H), 7.64 (d, J = 8.4 Hz, 1H), 6.87 (d, J
= 8.4 Hz, 1H), 3.96 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 161.5,
142.7, 134.1, 117.6, 110.7, 105.9, 86.0, 56.7.
2-Iodo-5-nitrobenzonitrile (2f). Yield 108 mg, 79%. 1H NMR (400
MHz, CDCl3) δ 8.44 (d, J = 2.5 Hz,1H), 8.20 (d, J = 8.7 Hz, 1H), 8.12
(dd, J1 = 2.5 Hz, J2 = 8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
147.7, 141.1, 128.7, 127.7, 122.4, 117.5, 106.9.
1
2-Iodo-5-bromobenzonitrile (2g). Yield 112 mg, 73%. H NMR
(400 MHz, CDCl3) δ 7.79 (d, J = 8.4 Hz, 1H), 7.74 (d, J = 2.4 Hz,
1H), 7.43 (dd, J1 = 2.4, J2 = 8.4 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 140.8, 137.0, 136.7, 122.4, 122.3, 118.0, 96.5.
2-Iodo-5-phenylbenzonitrile (2h). Yield 117 mg, 77%. Mp 63−64
°C. 1H NMR (400 MHz, CDCl3) δ 8.00 (d, J = 8.3 Hz, 1H), 7.83 (d, J
= 2.3 Hz, 1H), 7.55 (dd, J1 = 2.3 Hz, J2 = 8.0 Hz, 2H), 7.45−7.52 (m,
D
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Note
4H); 13C NMR (100 MHz, CDCl3) δ 141.9, 139.9, 137.9, 132.7,
132.3, 129.3, 128.8, 126.9, 121.2, 119.3, 96.5; HRMS (ESI) calcd for
C13H8IN[Na] 327.9599, found 327.9593.
13C NMR (100 MHz, CDCl3) δ 137.5, 134.8, 134.2, 132.5, 129.7,
116.1, 113.0, 20.6.
1
2-Chloro-4-methylbenzonitrile (4d). Yield 67 mg, 88%. H NMR
2-Iodo-3,5-dimethoxybenzonitrile (2i). Yield 127 mg, 88%. Mp.
99−100 °C. 1H NMR (400 MHz, CDCl3) δ 6.76 (d, J = 2.4 Hz, 1H),
6.57 (d, J = 2.4 Hz, 1H), 3.89 (s, 3H), 3.84 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 161.2, 159.9, 121.7, 119.4, 110.3, 103.2, 80.4, 56.8,
55.9; HRMS (ESI) calcd for C9H8INO2[Na] 311.9498, found
311.9529.
(400 MHz, CDCl3) δ 7.54 (d, J = 7.9 Hz, 1H), 7.33 (s, 1H), 7.17 (d, J
= 7.9 Hz, 1H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 145.5,
136.5, 133.7, 130.6, 128.1, 116.3, 110.2, 21.7.
2-Chloro-4-methoxybenzonitrile (4e). Yield 67 mg, 80%. 1H NMR
(400 MHz, CDCl3) δ 7.67 (d, J = 1.9 Hz, 1H), 7.57 (dd, J1 = 1.9 Hz, J2
= 8.6 Hz, 1H), 6.99 (d, J = 8.6 Hz, 1H), 3.98 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 163.4, 138.3, 135.0, 116.4, 115.6, 113.5, 105.0, 56.0.
2-Iodo-4,5-dimethoxybenzonitrile (2j). Yield 136 mg, 94%. Mp
1
1
4-Bromo-2-chlorobenzonitrile (4m). Yield 89 mg, 82%. H NMR
103−104 °C. H NMR (400 MHz, CDCl3) δ 7.23 (s, 1H), 7.01 (s,
(400 MHz, CDCl3) δ 7.73 (s, 1H), 7.55 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ 137.8, 134.6, 133.1, 130.8, 128.2, 115.3, 112.3.
1H), 3.91 (s, 3H), 3.87 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
152.8, 149.2, 121.4, 119.8, 115.7, 112.0, 88.7, 56.5, 56.3; HRMS (ESI)
calcd for C9H8INO2[Na] 311.9498, found 311.9455.
2-Chloro-4-nitrobenzonitrile (4l). Yield 76 mg, 83%. 1H NMR (400
MHz, CDCl3) δ 8.41 (d, J = 2.1 Hz, 1H), 8.26 (dd, J1 = 2.1 Hz, J2 =
8.5 Hz, 1H), 7.93 (d, J = 8.5 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
150.3, 138.6, 135.0, 125.2, 122.1, 119.1, 114.2.
1
8-Iodo-1-naphthonitrile (2k). Yield 85 mg, 61%. H NMR (400
MHz, CDCl3) δ 8.26 (d, J = 8.0 Hz, 1H), 7.99−8.02 (m, 2H), 7.85 (d,
J = 8.2 Hz, 1H), 7.48 (dd, J1 = 8.0 Hz, J2 = 8.0 Hz, 1H), 7.18 (t, J = 8.0
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 143.5, 138.8, 135.0, 134.6,
131.1, 130.4, 128.2, 125.3, 119.0, 112.5, 92.3.
2-Chloro-5-nitrobenzonitrile (4f). Yield 64 mg, 70%. 1H NMR
(400 MHz, CDCl3) δ 8.57 (d, J = 2.6 Hz, 1H), 8.42 (dd, J1 = 2.6 Hz, J2
= 8.9 Hz, 1H), 7.77 (d, J = 8.9 Hz, 1H); 13C NMR (100 MHz, CDCl3)
δ 146.3, 143.6, 131.3, 129.0, 128.4, 114.9, 114.0.
2-Bromobenzonitrile (3a). Yield 79 mg, 87%. 1H NMR (400 MHz,
CDCl3) δ 7.66−7.71 (m, 2H), 7.44−7.50 (m, 2H); 13C NMR (100
MHz, CDCl3) δ 134.3, 134.0, 133.2, 127.7, 125.3, 117.1, 115.8.
4-Bromo-2,6-dichlorobenzonitrile (5m). Yield 84 mg, 67%. 1H
NMR (400 MHz, CDCl3) δ 7.64 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ 139.0, 131.3, 127.8, 113.5, 112.9.
1
2-Bromo-6-methylbenzonitrile (3b). Yield 71 mg, 72%. H NMR
(400 MHz, CDCl3) δ 7.49 (d, J = 7.9 Hz, 1H), 7.34 (t, J = 7.9 Hz,
1H), 7.27 (d, J = 8.0 Hz, 1H), 2.58 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 144.8, 133.3, 130.3, 128.8, 125.5, 116.4, 116.2, 21.2.
1,3-Dimethoxy-5-((4-methoxyphenyl)ethynyl)benzene (6). Yield
222 mg, 83%. 1H NMR (400 MHz, CDCl3) δ 7.50 (d, J = 8.6 Hz, 2H),
6.90 (d, J = 8.6 Hz, 2H), 6.71 (d, J = 2.0 Hz, 2H), 6.47 (s, 1H), 3.84
(s, 3H), 3.82 (s, 6H); 13C NMR (100 MHz, CDCl3) δ 160.5, 159.7,
133.1, 124.9, 115.2, 114.0, 109.2, 101.6, 89.0, 88.1, 55.4, 55.3.
1
2-Bromo-5-methylbenzonitrile (3c). Yield 78 mg, 80%. H NMR
(400 MHz, CDCl3) δ 7.52 (d, J = 8.2 Hz, 1H), 7.34 (d, J = 1.8 Hz,
1H), 7.26 (dd, J1 = 8.2 Hz, J2 = 1.8 Hz, 1H), 2.35 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 138.2, 135.0, 134.6, 132.9, 121.8, 117.3, 115.4,
20.7.
1
Indenone (7a). Yield 32 mg, 30%. H NMR (400 MHz, CDCl3) δ
7.14 (d, J = 8.8 Hz, 2H), 6.88 (d, J = 2.4 Hz, 1H), 6.77 (d, J = 8.8 Hz,
2H), 6.52 (d, J = 2.4 Hz, 2H), 6.46 (t, J = 2.4 Hz, 2H), 3.88 (s, 3H),
3.79 (s, 3H), 3.72 (s, 6H), 3.63 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 196.6, 162.5, 160.2, 158.7, 156.6, 154.7, 137.0, 134.1, 131.0, 130.6,
123.6, 122.7, 113.4, 106.6, 104.1, 102.8, 101.0, 55.9, 55.8, 55.4, 55.2.
1
2-Bromo-4-methylbenzonitrile (3d). Yield 91 mg, 92%. H NMR
(400 MHz, CDCl3) δ 7.54 (d, J = 8.0 Hz, 1H), 7.52 (s, 1H), 7.22 (d, J
= 8.0 Hz, 1H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 145.4,
134.0, 133.8, 128.5, 125.1, 117.4, 116.1, 21.6.
1
Indenone (7b). Yield 46 mg, 43%. H NMR (400 MHz, CDCl3) δ
2-Bromo-4-methoxybenzonitrile (3e). Yield 84 mg, 79%. 1H NMR
(400 MHz, CDCl3) δ 7.80 (d, J = 1.9 Hz, 1H), 7.59 (dd, J1 = 1.9 Hz, J2
= 8.6 Hz, 1H), 6.95 (d, J = 8.6 Hz, 1H), 3.96 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 159.4, 136.6, 133.2, 117.7, 112.3, 112.0, 105.2, 56.6.
2-Bromo-5-nitrobenzonitrile (3f). Yield 95 mg, 84%. 1H NMR
(400 MHz, CDCl3) δ 8.51 (d, J = 2.6 Hz, 1H), 8.30 (dd, J1 = 2.6 Hz, J2
= 8.7 Hz, 1H), 7.94 (d, J = 8.7 Hz, 1H); 13C NMR (100 MHz, CDCl3)
δ 146.9, 134.6, 132.6, 129.1, 128.2, 117.4, 115.3.
7.31 (d, J = 8.4 Hz, 2H), 6.88 (d, J = 2.0 Hz, 1H), 6.85 (d, J = 8.4 Hz,
2H), 6.46 (d, J = 1.8 Hz, 1H), 6.32−6.33 (m, 3H), 3.88 (s, 3H), 3.84
(s, 3H), 3.63 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 195.8, 162.8,
160.1, 159.9, 158.9, 155.0, 134.5, 133.2, 130.5, 130.4, 126.9, 122.1,
112.9, 107.9, 103.9, 102.6, 100.1, 55.9, 55.7, 55.2, 55.1.
ASSOCIATED CONTENT
■
2,4-Dibromobenzonitrile (3m). Yield 108 mg, 83%. 1H NMR (400
MHz, CDCl3) δ 7.89 (d, J = 1.6 Hz, 1H), 7.59 (dd, J1 = 1.6 Hz, J2 =
8.3 Hz, 1H), 7.53 (d, J = 8.3 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
136.0, 134.9, 131.2, 128.3, 126.0, 116.5, 114.8.
S
* Supporting Information
Copies of 1H NMR and 13C NMR spectra for all products. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
2-Bromo-4-nitrobenzonitrile (3l). Yield 106 mg, 93%. H NMR
(400 MHz, CDCl3) δ 8.56 (d, J = 2.0 Hz, 1H), 8.29 (dd, J1 = 2.0 Hz, J2
= 8.5 Hz, 1H), 7.90 (d, J = 8.5 Hz, 1H); 13C NMR (100 MHz, CDCl3)
δ 150.0, 135.2, 128.2, 126.5, 122.6, 121.6, 115.5.
AUTHOR INFORMATION
Corresponding Author
*E-mail: sunpeipei@njnu.edu.cn.
Notes
■
1
2,5-Dibromobenzonitrile (3g). Yield 98 mg, 75%. H NMR (400
MHz, CDCl3) δ 7.79 (d, J = 2.1 Hz, 1H), 7.56−7.61 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ 137.1, 136.7, 134.5, 124.1, 121.2, 117.6,
115.8.
The authors declare no competing financial interest.
1
Methyl 3-Bromo-4-cyanobenzoate (3n). Yield 102 mg, 85%. H
ACKNOWLEDGMENTS
■
NMR (400 MHz, CDCl3) δ 8.35 (s, 1H), 8.08 (d, J = 8.0 Hz, 1H),
7.75 (d, J = 8.0 Hz, 1H), 3.98 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
164.3, 135.1, 134.3, 134.0, 128.4, 125.4, 119.6, 116.5, 53.0.
2-Chlorobenzonitrile (4a). Yield 62 mg, 90%. 1H NMR (400 MHz,
CDCl3) δ 7.69 (dd, J1 = 1.4 Hz, J2 = 8.0 Hz, 1H), 7.52−7.57 (m, 2H),
7.38−7.42 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 136.9, 134.0,
133.9, 130.1, 127.2, 116.0, 113.4.
This work was supported by the National Natural Science
Foundation of China (Project 21272117 and 20972068) and
the Priority Academic Program Development of Jiangsu Higher
Education Institutions.
REFERENCES
■
1
2-Chloro-6-methylbenzonitrile (4b). Yield 54 mg, 71%. H NMR
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1
2-Chloro-5-methylbenzonitrile (4c). Yield 62 mg, 82%. H NMR
(400 MHz, CDCl3) δ 7.47 (s, 1H), 7.33−7.41 (m, 2H), 2.38 (s, 3H);
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