Palladium-catalyzed ortho-arylation of benzamides via direct sp2 C-H bond activation

Article abstract of DOI:10.1021/jo300126n

The palladium-catalyzed ortho-arylation of benzamides by aryl iodides has been demonstrated with the simplest amide CONH₂ as a directing group for the first time. This protocol can be applied to various benzamides and aryl iodides with both electron-donating and electron-withdrawing groups. In addition, the synthesized biphenyl-2-carboxamides can be further transformed to other biphenyl derivatives such as nitriles, carboxylic acids, carbamates, and amines.

Full text of DOI:10.1021/jo300126n

Article
pubs.acs.org/joc
Palladium-Catalyzed Ortho-Arylation of Benzamides via Direct sp2
C−H Bond Activation
Dan-Dan Li,† Ting-Ting Yuan,† and Guan-Wu Wang*,†,‡
†CAS Key Laboratory of Soft Matter Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Joint Laboratory of
Green Synthetic Chemistry, and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026,
P. R. China
‡State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, Gansu 730000, People’s Republic of China
S
* Supporting Information
ABSTRACT: The palladium-catalyzed ortho-arylation of
benzamides by aryl iodides has been demonstrated with the
simplest amide CONH2 as a directing group for the first time.
This protocol can be applied to various benzamides and aryl
iodides with both electron-donating and electron-withdrawing
groups. In addition, the synthesized biphenyl-2-carboxamides
can be further transformed to other biphenyl derivatives such
as nitriles, carboxylic acids, carbamates, and amines.
CONH2 group to afford biphenyl-2-carboxamides, which can
be further converted to other biphenyl derivatives.
INTRODUCTION
■
The biaryl subunit is a key structural motif for the preparation
of a wide range of natural products, biologically active phar-
maceuticals, polymers, metal ligands for catalysis, and liquid
crystals.1 Over the past decades, cross-coupling reactions, i.e.,
Suzuki−Miyaura, Kumada, Negishi, Stille, and Hiyama
reactions, have emerged as the most useful synthetic methods
to construct aryl−aryl bonds.2 Despite the widespread ap-
plication, these methods usually require the prefunctionalized
starting materials and auxiliary ligands that are often expen-
sive or difficult to prepare. To overcome these drawbacks,
transition-metal-catalyzed direct arylation via the cleavage of sp2
C−H bond to construct C−C bonds has received extensive
attention in recent years.3 Directing group-assisted activation of
ortho aromatic C−H bonds has been widely investigated, and
various directing groups such as acylamino,4 pyridyl,5 carboxyl,6
oxazolyl,7 hydroxyl,8 and oxime9 groups have been used for
palladium-catalyzed C−H bond activation. It is worthy of note
that transition-metal-free processes to approach the cross
coupling of aryl halides and arenes have been successfully
realized.10 In recent years, amide as a directing group has
attracted substantial interest. Miura,11 Daugulis,12 Yu,13
Dong,14 and our group15 have independently reported the
Pd-catalyzed arylation reactions between N-substituted amides
RCONHR′ and aryl halides or simple arenes. The Pd-catalyzed
reaction of both N-aryl11,13a,b and N-alkyl12 amides with aryl
halides tended to afford significantly or even exclusively diary-
lation products and remains a challenge for selective mono-
arylation. Until now, extension to the simplest amide CONH2
as a directing group to form arylation products catalyzed by
palladium has never been reported. Herein, we report the
palladium-catalyzed highly regioselective monoarylation of
benzamides ArCONH2 with aryl iodides directed by the
RESULTS AND DISCUSSION
■
Recently, we have reported palladium-catalyzed sp2 C−H acti-
vation reactions using directing groups including the −NHOCCH3
and −CONHOCH3 groups to construct C−C, C−O, and
C−N bonds.15,16 Prompted by the success, we wondered
whether the N-unsubstituted amide −CONH2 could also be
used as a directing group to facilitate the C−H arylation reac-
tion with aryl iodides. In the initial study, we focused on
benzamide (1a) and iodobenzene (2a) as the model substrates
to screen the optimal conditions.
It is known that the combination of ArI and AgOAc has
broad applications in the Pd-catalyzed arylation reactions of
ArNHR, ArCONHR, and other substrates.4f,12,17 Therefore, we
first chose AgOAc as the additive. As desired, product 3aa was
isolated in 64% yield after 5 h (Table 1, entry 1). To our
delight, when Ag2O was used, the yield was improved to 74%
(Table 1, entry 2) accompanied by 5% of diarylation product
and ∼1% of the cyclized product, i.e., phenanthridinone. If the
reaction time was prolonged to 36 h, the yield dropped to 44%
(Table 1, entry 3) together with more byproducts (7% of
diarylation product and 3% of phenanthridinone). Thus, we
could conclude that the CONH2 group behaved quite
differently from the CONHOCH3 group because the latter
preferred to afford the cyclized product N-methoxyphenan-
thridinone in 76% yield under the same conditions.15 The
efficiency of other silver salts was also examined; Ag2SO4 and
Ag2CO3 could promote the reaction, but both of them failed
to give a better yield than Ag2O (Table 1, entries 4 and 5).
Received: January 20, 2012
Published: March 26, 2012
© 2012 American Chemical Society
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The Pd-catalyzed reaction of benzamide 1a with 2b, 2c, 2d, and
2e produced 3ab, 3ac, 3ad, and 3ae in 84%, 71%, 68%, and
57% yields, respectively (Table 2, entries 11−14). Similarly, the
reaction of p- and m-methyl-substituted benzamides 1b and 1c
with 2b−d afforded 3bb−bd and 3cb−cd in 50−78% yields
(Table 2, entries 15−20). To our delight, when electron-rich
substrate 1f was allowed to react with 2b−d, products 3fb−fd
were obtained in higher yields (70−82%) (Table 2, entries
21−23). It should be pointed out that the Pd-catalyzed
arylation of benzamides 1 with aryl iodides 2 also gave a small
amount of diarylated benzamides (0−9%) and phenanthridi-
nones (<3%) as byproducts in most cases. However, the predo-
minant monoarylation of N-unsubstituted benzamides ArCONH2
with our protocol was intriguing because N-substituted
benzamides ArCONHR usually afforded diarylation products
except for sterically demanding meta-substituted benzamides.11,12
Aromatic amides and their derivatives are important inter-
mediates of pharmaceuticals, pesticides, and dyes. The CONH2
group is a valuable precursor for various functional groups such
as nitrile, carboxylic acid, carbamate, and amine, as exemplified
by 3aa (Scheme 1). Treatment of 3aa with a catalytic amount
of PdCl2 in a mixture of CH3CN and H2O at room temperature
for 6 h afforded biphenyl-2-carbonitrile 4aa in 95% yield.
Hydrolysis of 3aa in 30% H2SO4 at 120 °C for 24 h led to
biphenyl-2-carboxylic acid 5aa in 98% yield. Reaction of 3aa
with PhI(OAc)2 in KOH−MeOH in the range of 0 °C to room
temperature for 1 h generated methyl biphenyl-2-ylcarbamate
6aa, which could be further converted to biphenyl-2-amine 7aa
in a total yield of 92%. Interestingly, when 3aa was treated with
60% H2SO4 at 140 °C for 36 h, 9-fluorenone 8aa was directly
achieved in 87% yield. Fluorenones have been synthesized
by the Pd-catalyzed ortho-arylation of N-propylbenzamides,
followed by dehydration with (CF3CO)2O.12b
Table 1. Screening Conditions for the Pd-Catalyzed
Reaction of Benzamide and Iodobenzene
a
entry
additive
solvent
yield (%)
1
AgOAc
Ag2O
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
DCE
64
2
74
44
b
3
Ag2O
4
5
6
7
8
9
Ag2SO4
Ag2CO3
Ag2O
61
73
11
Ag2O
toluene
17
Ag2O
dioxane
18
Ag2O
DMF
trace
a
Unless otherwise specified, all reactions were carried out with 0.5
mmol of 1a, 1.0 mmol of 2a, 0.025 mmol of Pd(OAc)2, and 1.0 mmol
b
of additive in 5 mL of solvent at 120 °C for 5 h. 36 h.
In addition, the effect of solvent was explored. Disappointingly,
when DCE, toluene, and 1,4-dioxane were employed as the
solvent, the product was isolated in very low yield (Table 1,
entries 6−9). Therefore, 1 equiv of 1a, 2 equiv of 2a, and 2
equiv of Ag2O were chosen as the optimized conditions for the
Pd-catalyzed reaction of 1a with 2a in refluxing AcOH at 120 °C.
With the optimized reaction conditions in hand, we started
to investigate the scope and limitations of the reaction. The
reaction conditions and product yields are listed in Table 2.
Benzamides 1b−k with either electron-donating or electron-
withdrawing groups could react with iodobenzene (2a) to
obtain the desired products 3ba−ka (Table 2, entries 1−10).
Substrates 1b−d bearing a methyl group at the meta-position
and/or para-position of the phenyl ring reacted with 2a
smoothly to give the corresponding products 3ba−da in 58−
68% yields (Table 2, entries 1−3). O-Methyl substitution on
the phenyl ring of 1e reduced the product yield only slightly
(Table 2, entry 4 vs entries 1−3), not exhibiting an obvious
“ortho-substituent” effect.15,16 In comparison, the strong
electron-donating methoxy group at the meta-position could
also afford 3fa in 68% yield (Table 2, entry 5), whereas the
methoxy group at the para-position provided 3ga in only 34%
yield with some starting material remained unchanged even
after prolonging the reaction time to 24 h (Table 2, entry 6).
Substrates 1h−j with halogen atoms including chlorine and
bromine were tolerated under the employed reaction con-
ditions and afforded 3ha−ja in 34−54% yields (Table 2, entries
7−9). Gratifyingly, benzamide 3k bearing the strong electron-
withdrawing p-NO2 group could also be functionalized to bring
out the desired product, albeit at a relatively low yield even with
a prolonged reaction time (Table 2, entry 10). The above
substituent effects clearly disclose the electrophilic nature for
the C−H activation process because substrates with electron-
donating groups generally gave higher yields than those with
electron-withdrawing groups (Table 2, entries 1−5 vs entries
7−10).
CONCLUSION
■
In summary, we have demonstrated the Pd-catalyzed regio-
selective ortho-arylation of benzamides by aryl iodides using the
simplest amide CONH2 as a directing group for the first time.
Our protocol can be applied to a wide range of benzamides and
aryl iodides with both electron-donating and electron-with-
drawing groups. The obtained biphenyl-2-carboxamides can be
further manipulated to construct a variety of biphenyl deriva-
tives such as nitriles, carboxylic acids, carbamates, and amines
and thus may provide a new strategy for the synthesis of drugs
and natural products.
EXPERIMENTAL SECTION
■
General Procedure for the Direct Ortho-Arylation of
Benzamide 1a (1b−k) Catalyzed by Pd(OAc)2. To a stirred
solution of benzamide 1a (1b−k, 0.5 mmol), Pd(OAc)2 (5.6 mg,
0.025 mmol), and aryl iodide 2a (2b−e, 1 mmol) in AcOH (5 mL) at
120 °C was added Ag2O (231.7 mg, 1 mmol). The reaction was
monitored by TLC and stopped at the desired time. Then the solvent
was evaporated to dryness in vacuo. The residual was separated on a
silica gel column with petroleum ether/ethyl acetate 2/1 as the eluent
to give desired product 3aa (3ba−ka, 3ab−ae, 3bb−bd, 3cb−cd, and
3fb−fd) along with small amounts of less polar diarylation products
and phenanthridinones in most cases.
Biphenyl-2-carboxamide (3aa).18 White solid; mp 176−178 °C;
1H NMR (400 MHz, CDCl3) δ 7.81 (dd, J = 7.2, 1.4 Hz, 1H), 7.51
1-Iodo-4-methylbenzene (2b), 1-iodo-4-methoxybenzene
(2c), 1-iodo-3-methoxybenzene (2d), and 1-chloro-4-iodoben-
zene (2e) were then chosen as other representative aryl iodides
to examine the cross-coupling reaction (Table 2, entries 11−23).
(td, J = 7.6, 1.6 Hz, 1H), 7.47−7.39 (m, 6H), 7.37 (dd, J = 7.4, 1.0 Hz, 1H),
5.50 (1H, bs), 5.24 (1H, bs).
5-Methylbiphenyl-2-carboxamide (3ba). White solid; mp 143−
144 °C; 1H NMR (400 MHz, CDCl3) δ 7.74 (dd, J = 8.0, 3.0 Hz, 1H),
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a
Table 2. Pd-Catalyzed Direct Ortho-Arylation of Benzamides
a
All reactions were carried out with 0.5 mmol of 1, 1.0 mmol of 2, 0.025 mmol of Pd(OAc)2, and 1.0 mmol of Ag2O in 5 mL of AcOH at 120 °C.
b
c
Isolated yield; the yield in parentheses corresponds to that of diarylation product. Trace amount.
7.49−7.35 (m, 4H), 7.35−7.20 (m, 2H), 7.16 (s, 1H), 5.43 (bs, 1H),
5.19 (bs, 1H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.4,
141.0, 140.6, 140.1, 131.3, 129.5, 128.9 (2C), 128.8 (2C), 128.5, 128.0,
127.5, 21.5. IR (KBr) ν 3375, 3178, 1643, 1392, 1133, 822, 702,
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HRMS (EI-TOF) m/z [M+] calcd for C13H10NO35Cl, 231.0451, found
231.0449.
Scheme 1. Transformation of Biphenyl-2-carboxamide
4,5-Dichlorobiphenyl-2-carboxamide (3ia). White solid; mp
178−180 °C; 1H NMR (300 MHz, CDCl3) δ 7.93 (s, 1H), 7.47−7.39
(m, 6H), 5.46 (bs, 1H), 5.20 (bs, 1H); 13C NMR (100 MHz, CDCl3)
δ 168.9, 139.8, 138.0, 134.9, 133.7, 132.33, 132.29, 131.4, 129.2 (2C),
128.9, 128.8 (2C); IR (KBr) ν 3386, 3189, 1645, 1472, 1392, 1346,
1150, 1023, 892, 773, 700, 648, 569 cm−1; HRMS (EI-TOF) m/z
[M+] calcd for C13H9NO35Cl2 265.0061, found 265.0053.
5-Bromobiphenyl-2-carboxamide (3ja). White solid; mp 158−
159 °C; 1H NMR (400 MHz, CDCl3) δ 7.69 (d, J = 8.4 Hz, 1H), 7.57
(dd, J = 8.0, 2.0 Hz, 1H), 7.53 (d, J = 2.0 Hz, 1H), 7.48−7.40 (m, 5H),
5.47 (bs, 1H), 5.19 (bs, 1H); 13C NMR (100 MHz, CDCl3) δ 170.4,
141.9, 138.9, 133.4, 133.2, 131.0, 130.9, 129.0 (2C), 128.8 (2C), 128.7,
125.0; IR (KBr) ν 3379, 3184, 1647, 1554, 1480, 1388, 1082, 887,
816, 772, 702, 660 cm−1; HRMS (EI-TOF) m/z [M+] calcd for
C13H10NO79Br 274.9946, found 274.9940.
5-Nitrobiphenyl-2-carboxamide (3ka). Yellow solid; mp 182−
184 °C; 1H NMR (400 MHz, CDCl3) δ 8.28−8.25 (m, 2H), 7.93 (dd,
J = 7.4, 1.4 Hz, 1H), 7.51−7.47 (m, 5H), 5.61 (bs, 1H), 5.29 (bs, 1H);
13C NMR (100 MHz, CDCl3) δ 169.3, 148.9, 141.5, 140.1, 138.0,
130.5, 129.30 (2C), 129.25 (2C), 128.8, 125.4, 122.5; IR (KBr) ν
3378, 3190, 1647, 1519, 1392, 1356, 912, 849, 796, 776, 732, 663, 549
cm−1; HRMS (EI-TOF) m/z [M+] calcd for C13H10N2O3 242.0691,
found 242.0691.
668 cm−1; HRMS (EI-TOF) m/z [M+] calcd for C14H13NO 211.0997,
found 211.0991.
4-Methylbiphenyl-2-carboxamide (3ca). White solid; mp 172−
1
174 °C; H NMR (400 MHz, CDCl3) δ 7.62 (d, J = 1.2 Hz, 1H),
4′-Methylbiphenyl-2-carboxamide (3ab). White solid; mp
7.44−7.24 (m, 7H), 5.41 (bs, 1H), 5.19 (bs, 1H), 2.43 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 171.5, 140.4, 137.8, 137.2, 134.2, 131.5,
130.5, 129.8, 129.0 (2C), 128.8 (2C), 127.9, 21.1; IR (KBr) ν 3387,
3184, 1645, 1482, 1411, 1383, 822, 772, 702, 644 cm−1; HRMS (EI-
TOF) m/z [M+] calcd for C14H13NO 211.0997, found 211.0991.
4,5-Dimethylbiphenyl-2-carboxamide (3da). White solid; mp
139−140 °C; 1H NMR (300 MHz, CDCl3) δ 7.64 (s, 1H), 7.47−7.35
(m, 5H), 7.12 (s, 1H), 5.51 (bs, 1H), 5.21 (bs, 1H), 2.34 (s, 3H), 2.33
(s, 3H); 13C NMR (75 MHz, CDCl3) δ 171.6, 140.4, 139.5, 137.6,
136.2, 131.8, 131.6, 130.5, 128.9 (2C), 128.7 (2C), 127.7, 19.7, 19.3;
IR (KBr) ν 3385, 3186, 1643, 1486, 1448, 1400, 1101, 890, 773, 702,
653 cm−1; HRMS (EI-TOF) m/z [M+] calcd for C15H15NO 225.1154,
found 225.1147.
1
138−139 °C; H NMR (400 MHz, CDCl3) δ 7.80 (dd, J = 7.6, 1.6
Hz, 1H), 7.49 (td, J = 7.6, 1.6 Hz, 1H), 7.41 (td, J = 7.6, 1.2 Hz, 1H),
7.36−7.33 (m, 3H), 7.24 (d, J = 8.0 Hz, 2H), 5.41 (bs, 1H), 5.25 (bs,
1H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.4, 140.0,
138.0, 137.4, 134.4, 130.7, 130.6, 129.6 (2C), 129.3, 128.9 (2C), 127.6,
21.3; IR (KBr) ν 3372, 3183, 1643, 1483, 1396, 1130, 824, 756, 666,
631, 542, 512 cm−1; HRMS (EI-TOF) m/z [M+] calcd for C14H13NO
211.0997, found 211.1001.
4′-Methoxybiphenyl-2-carboxamide (3ac). White solid; mp
102−104 °C; 1H NMR (400 MHz, CDCl3) δ 7.77 (dd, J = 7.6, 1.2 Hz,
1H), 7.48 (td, J = 7.6, 1.2 Hz, 1H), 7.39 (td, J = 7.6, 1.2 Hz, 1H), 7.37
(d, J = 8.8 Hz, 2H), 7.34 (dd, J = 7.6, 1.2 Hz, 1H), 6.96 (d, J = 8.8 Hz,
2H), 5.65 (bs, 1H), 5.29 (bs, 1H), 3.85 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 171.7, 159.6, 139.6, 134.4, 132.6, 130.6, 130.5, 130.1 (2C),
129.2, 127.4, 114.3 (2C), 55.4; IR (KBr) ν 3368, 3186, 1650, 1574,
1478, 1445, 1392, 1096, 1004, 835, 759, 689, 633, 512 cm−1; HRMS
3-Methylbiphenyl-2-carboxamide (3ea). White solid; mp 124−
1
126 °C; H NMR (300 MHz, CDCl3) δ 7.49−7.32 (m, 6H), 7.22 (t,
J = 7.4 Hz, 2H), 5.54 (bs, 1H), 5.27 (bs, 1H), 2.47 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 172.2, 140.5, 139.0, 135.8, 135.4, 129.5, 129.1,
128.7 (2C), 128.5 (2C), 127.6, 127.5, 19.6; IR (KBr) ν 3362, 3184,
1645, 1611, 1459, 1435, 1357, 758, 701 cm−1; HRMS (EI-TOF) m/z
[M+] calcd for C14H13NO 211.0997, found 211.0984.
+
(ESI) m/z (M + H+) calcd for C14H14NO2 228.1019, found
228.1021.
3′-Methoxybiphenyl-2-carboxamide (3ad). White solid; mp
99−100 °C; 1H NMR (400 MHz, CDCl3) δ 7.81 (dd, J = 7.6, 1.6 Hz,
1H), 7.50 (td, J = 7.6, 1.6 Hz, 1H), 7.44 (td, J = 7.6, 1.6 Hz, 1H), 7.36
(dd, J = 7.6, 1.6 Hz, 1H), 7.35 (t, J = 8.0 Hz, 1H), 7.02 (ddd, J = 7.6,
1.6, 0.8 Hz, 1H), 6.98 (dd, J = 2.4, 1.6 Hz, 1H), 6.94 (ddd, J = 7.6, 2.4,
0.8 Hz, 1H), 5.43 (bs, 1H), 5.28 (bs, 1H), 3.83 (s, 1H); 13C NMR
(100 MHz, CDCl3) δ 171.4, 159.8, 141.8, 139.9, 134.5, 130.6, 130.4,
129.9, 129.2, 127.8, 121.3, 114.4, 113.8, 55.4; IR (KBr) ν 3371, 3176,
1649, 1623, 1577, 1450, 1401, 1295, 1211, 1118, 1049, 874, 778, 689,
635, 530 cm−1; HRMS (EI-TOF) m/z [M+] calcd for C14H13NO2
227.0946, found 227.0941.
4′-Chlorobiphenyl-2-carboxamide (3ae). Pale yellow solid, mp
162−164 °C; 1H NMR (300 MHz, CDCl3) δ 7.77 (d, J = 8.1 Hz, 1H),
7.48−7.35 (m, 7H), 5.65 (bs, 1H), 5.21 (bs, 1H); 13C NMR (100
MHz, CDCl3) δ 171.5, 140.3, 140.0, 134.5, 130.7, 130.5, 129.2, 128.9
(2C), 128.8 (2C), 128.1, 127.7; IR (KBr) ν 3385, 3174, 1643, 1618,
1450, 1398, 1113, 776, 742, 697, 634, 573 cm−1; HRMS (ESI) m/z
(M + H+) calcd for C13H11NO35Cl+ 232.0524, found 232.0533.
4′,5-Dimethylbiphenyl-2-carboxamide (3bb). White solid; mp
141−142 °C; 1H NMR (400 MHz, CDCl3) δ 7.75 (d, J = 7.6 Hz, 1H),
7.31 (d, J = 8.0 Hz, 2H), 7.25−7.22 (m, 3H), 7.14 (d, J = 1.2 Hz, 1H),
5.72 (bs, 1H), 5.29 (bs, 1H), 2.41 (s, 3H), 2.40 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 171.4, 140.9, 140.1, 137.9, 137.6, 131.4, 131.3,
129.6, 129.5 (2C), 128.8 (2C), 128.3, 21.4, 21.3; IR (KBr) ν 3370,
3178, 1642, 1497, 1393, 1264, 1136, 826, 745, 711, 664, 588, 550,
4-Methoxybiphenyl-2-carboxamide (3fa). White solid; mp
1
161−162 °C; H NMR (400 MHz, CDCl3) δ 7.43−7.36 (m, 5H),
7.34 (d, J = 2.8 Hz, 1H), 7.28 (d, J = 8.4 Hz, 1H), 7.05 (dd, J = 8.4,
2.8 Hz, 1H), 5.42 (bs, 1H), 5.21 (bs, 1H), 3.88 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 171.0, 159.2, 140.1, 135.3, 132.5, 131.9, 129.1
(2C), 128.8 (2C), 127.8, 117.3, 113.7, 55.7; IR (KBr) ν 3382, 3173,
1646, 1599, 1486, 1409, 1388, 1298, 1276, 1233, 1041, 912, 866, 828,
+
771, 702 cm−1; HRMS (ESI) m/z (M + H+) calcd for C14H14NO2
228.1019, found 228.1023.
5-Methoxybiphenyl-2-carboxamide (3ga). White solid; mp
183−184 °C; 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 8.8 Hz, 1H),
7.47−7.38 (m, 6H), 6.96 (dd, J = 8.8, 2.8 Hz, 1H), 6.83 (d, J = 2.8 Hz,
1H), 5.42 (bs, 1H), 5.13 (bs, 1H), 3.87 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 170.6, 161.3, 142.2, 140.5, 131.7, 128.91 (2C), 128.88 (2C),
128.3, 126.5, 115.9, 113.2, 55.6; IR (KBr) ν 3370, 3176, 1644, 1624,
1561, 1488, 1391, 1294, 1215, 1182, 1128, 1036, 1017, 887, 815, 769,
703, 594 cm−1; HRMS (EI-TOF) m/z [M+] calcd for C14H13NO2
227.0946, found 227.0942.
5-Chlorobiphenyl-2-carboxamide (3ha). White solid; mp 155−
1
156 °C; H NMR (400 MHz, CDCl3) δ 7.77 (d, J = 8.4 Hz, 1H),
7.45−7.39 (m, 6H), 7.36 (d, J = 2.0 Hz, 1H), 5.45 (bs, 1H), 5.18 (bs,
1H); 13C NMR (100 MHz, CDCl3) δ 170.2, 141.7, 139.1, 136.7,
132.7, 130.9, 130.5, 129.0 (2C), 128.8 (2C), 128.7, 127.9; IR (KBr) ν
3378, 3189, 1644, 1382, 1090, 885, 832, 774, 703, 662, 549 cm−1;
3344
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517 cm−1; HRMS (ESI) m/z (M + H+) calcd for C15H16NO+
226.1226, found 226.1218.
J = 8.5, 2.8 Hz, 1H), 6.99 (ddd, J = 7.6, 1.5, 1.0 Hz, 1H), 6.94 (dd, J =
2.6, 1.5 Hz, 1H), 6.91 (ddd, J = 8.2, 2.6, 1.0 Hz, 1H), 5.46 (bs, 1H),
5.28 (bs, 1H), 3.88 (s, 3H), 3.83 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 171.2, 159.8, 159.2, 141.5, 135.4, 132.3, 131.7, 129.8, 121.4,
117.1, 114.5, 113.6, 113.4, 55.6, 55.4; IR (KBr) ν 3371, 3176, 1648,
1599, 1478, 1407, 1300, 1236, 1055, 1016, 861, 824, 780, 737, 702,
4′-Methoxy-5-methylbiphenyl-2-carboxamide (3bc). White
1
solid; mp 142−143 °C; H NMR (400 MHz, CDCl3) δ 7.69 (d, J =
7.6 Hz, 1H), 7.34 (d, J = 8.8 Hz, 2H), 7.19 (d, J = 7.6 Hz, 1H), 7.13 (s,
1H), 6.94 (d, J = 8.8 Hz, 2H), 5.84 (bs, 1H), 5.29 (bs, 1H), 3.84 (s,
3H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.6, 159.6,
140.8, 139.7, 132.8, 131.4, 131.3, 130.1 (2C), 129.5, 128.1, 114.2 (2C),
55.4, 21.4; IR (KBr) ν 3376, 3178, 1647, 1605, 1474, 1431, 1406,
1382, 1299, 1270, 1217, 1134, 1054, 1047, 1022, 887, 855, 823, 789,
780, 701, 649 cm−1; HRMS (ESI) m/z (M + H+) calcd for
+
668 cm−1; HRMS (ESI) m/z calcd for C15H16NO3 258.1125, found
258.1117.
Synthesis of Biphenyl-2-carbonitrile (4aa).19 By following a
reported procedure,20 3aa (49.3 mg, 0.25 mmol) in a mixture of H2O/
CH3CN = 1:1 (6 mL) was treated with PdCl2 (4.5 mg, 0.025 mmol) at
room temperature for 6 h. The reaction mixture was quenched with
water and extracted with diethyl ether (10 mL × 3). The solvent was
removed in vacuo and the residual was separated on a silica gel column
with petroleum ether/ethyl acetate 6/1 as the eluent to give 4aa (42.7
mg, 95%) as a white solid: mp 35−37 °C; 1H NMR (400 MHz,
CDCl3) δ 7.77 (dd, J = 7.8, 1.0 Hz, 1H), 7.65 (td, J = 7.6, 1.6 Hz, 1H),
7.58−7.42 (m, 7H).
+
C15H16NO2 242.1176, found 242.1169.
3′-Methoxy-5-methylbiphenyl-2-carboxamide (3bd). White
1
solid; mp 108−110 °C; H NMR (400 MHz, CDCl3) δ 7.73 (s, 1H),
7.33 (t, J = 8.0 Hz, 1H), 7.23 (d, J = 8.0 Hz, 1H), 7.15 (s, 1H), 7.01−
6.90 (m, 3H), 5.67 (bs, 1H), 5.29 (bs, 1H), 3.82 (s, 3H), 2.41 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 171.2, 159.8, 142.0, 140.9, 140.0,
131.4, 131.1, 129.8, 129.5, 128.5, 121.3, 114.4, 113.7, 55.4, 21.4; IR
(KBr) ν 3376, 3194, 1646, 1600, 1473, 1429, 1397, 1376, 1299, 1229,
1209, 1179, 1037, 862, 792, 699 cm−1; HRMS (ESI) m/z (M + H+)
Synthesis of Biphenyl-2-carboxylic Acid (5aa).21 By following
a modified procedure,22 the solution of 3aa (49.3 mg, 0.25 mmol) in
2.5 mL of 30% (v/v) sulfuric acid were heated at 120 °C with stirring
for 24 h. After being cooled to room temperature, the reaction mixture
was quenched with water and extracted with diethyl ether (10 mL × 3).
The solvent was removed under vacuum and the residual was separated
on a silica gel column with petroleum ether/ethyl acetate 3/1 as the
eluent to afford 5aa (48.4 mg, 98%) as a white solid: mp 108−110 °C;
1H NMR (400 MHz, CDCl3) δ 7.95 (dd, J = 7.6, 1.2 Hz, 1H), 7.56
(td, J = 7.6, 1.2 Hz, 1H), 7.45−7.32 (m, 7H).
+
calcd for C15H16NO2 242.1176, found 242.1165.
4,4′-Dimethylbiphenyl-2-carboxamide (3cb). White solid; mp
210−211 °C; 1H NMR (400 MHz, CDCl3) δ 7.63 (s, 1H), 7.33−7.29
(m, 3H), 7.25−7.22 (m, 3H), 5.59 (bs, 1H), 5.29 (bs, 1H), 2.42 (s,
3H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.6, 137.8,
137.5, 137.4, 137.2, 134.1, 131.5, 130.5, 129.9, 129.5 (2C), 128.9 (2C),
21.3, 21.1; IR (KBr) ν 3385, 3174, 1698, 1643, 1482, 1431, 1375,
1111, 1007, 895. 812, 728, 626, 595, 527 cm−1; HRMS (ESI) m/z
(M + H+) calcd for C15H16NO+ 226.1226, found 226.1218.
Synthesis of Methyl Biphenyl-2-ylcarbamate (6aa). By
following a reported process,23 3aa (49.3 mg, 0.25 mmol) was
added to a solution of KOH (35.3 mg, 0.63 mmol) in MeOH
(2.5 mL) and was stirred at room temperature until a homogeneous
solution was obtained, then cooled to 5−10 °C in an ice−water bath.
Diacetoxyiodobenzene (80.9 mg, 0.25 mmol) was added in one
portion and dissolved within 5 min. The reaction was stirred at ice-
bath temperature for 15 min followed by warming to room tem-
perature while stirring for an additional 45 min. Upon completion of
the reaction (TLC), the methanol was removed in vacuo and the
reaction mixture was quenched with water and extracted with CH2Cl2
(10 mL × 3). The solvent was removed in vacuo and the residual was
separated on a silica gel column with petroleum ether/ethyl acetate 6/1
as the eluent to give methyl biphenyl-2-ylcarbamate 6aa (52.6 mg,
93%) as a white solid: mp 184−185 °C; 1H NMR (400 MHz, CDCl3)
δ 8.14 (d, J = 8.0 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.43−7.34 (m,
4H), 7.21 (dd, J = 7.6, 1.6 Hz, 1H), 7.13 (td, J = 7.6, 1.2 Hz, 1H), 6.65
(bs, 1H), 3.71 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 154.1, 138.2,
135.0, 131.6, 130.3, 129.4 (2C), 129.3 (2C), 128.7, 128.1, 123.5, 119.7,
52.4; IR (KBr) ν 3422, 2952, 1740, 1586, 1522, 1449, 1305, 1213,
1069, 750, 704 cm−1; HRMS (ESI) m/z (M + H+) calcd for
4′-Methoxy-4-methylbiphenyl-2-carboxamide (3cc). White
1
solid; mp 99−101 °C; H NMR (400 MHz, CDCl3) δ 7.60 (d, J =
1.6 Hz, 1H), 7.35 (d, J = 8.4 Hz, 2H), 7.27 (dd, J = 8.0, 1.6 Hz, 2H),
7.22 (d, J = 8.0 Hz, 1H), 6.95 (d, J = 8.4 Hz, 2H), 5.56 (bs, 1H), 5.25
(bs, 1H), 3.84 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 171.8, 159.5, 137.3, 136.8, 134.1, 132.6, 131.4, 130.5, 130.1 (2C),
129.8, 114.2 (2C), 55.4, 21.0; IR (KBr) ν 3381, 3180, 1642, 1611,
1518, 1491, 1377, 1299, 1246, 1177, 1108, 1039, 818, 593, 534 cm−1;
+
HRMS (ESI) m/z (M + H+) calcd for C15H16NO2 242.1176, found
242.1169.
3′-Methoxy-4-methylbiphenyl-2-carboxamide (3cd). White
solid; mp 147−148 °C; 1H NMR (400 MHz, CDCl3) δ 7.63−7.62 (m,
1H), 7.33 (t, J = 7.8 Hz, 1H), 7.32−7.29 (m, 1H), 7.25 (d, J = 7.6 Hz,
1H), 7.00 (ddd, J = 7.8, 1.6, 1.0 Hz, 1H), 6.96 (dd, J = 2.4, 1.6 Hz,
1H), 6.92 (ddd, J = 8.4, 2.4, 1.0 Hz, 1H), 5.43 (bs, 1H), 5.26 (bs, 1H),
3.83 (s, 3H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.5,
159.8, 141.8, 137.8, 137.1, 134.1, 130.4, 129.9, 129.8, 121.4, 114.5,
113.6, 55.4, 21.1; IR (KBr) ν 3392, 3180, 1640, 1518, 1490, 1427,
1375, 1300, 1245, 1177, 1108, 1040, 818, 594, 553 cm−1; HRMS (ESI)
+
m/z (M + H+) calcd for C15H16NO2 242.1176, found 242.1169.
+
4-Methoxy-4′-methylbiphenyl-2-carboxamide (3fb). White
C14H14NO2 228.1019, found 228.1016.
1
solid; mp 164−166 °C; H NMR (400 MHz, CDCl3) δ 7.35 (d, J =
Synthesis of Biphenyl-2-amine (7aa).24 According to a
reported procedure,25 to a solution of 6aa (48.1 mg, 0.21 mmol) in
methanol (4 mL) was added 40% KOH solution (2 mL), and the
mixture was refluxed for 2 h. After being cooled to room temperature,
the mixture was diluted with EtOAc. The organic phase was washed
with brine, dried over Na2SO4, and concentrated in vacuo. The
residual was separated on a silica gel column with petroleum ether/
ethyl acetate 6/1 as the eluent to obtain 7aa (35.4 mg, 99%) as a white
2.8 Hz, 1H), 7.30 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.4 Hz, 1H), 7.22
(d, J = 8.0 Hz, 2H), 7.03 (dd, J = 8.4, 2.8 Hz, 1H), 5.41 (bs, 1H), 5.24
(bs, 1H), 3.88 (s, 3H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 171.1, 159.1, 137.6, 137.2, 135.2, 132.5, 131.9, 129.6 (2C), 129.0
(2C), 117.4, 113.7, 55.7, 21.3; IR (KBr) ν 3385, 3185, 1650, 1600,
1493, 1385, 1298, 1232, 1094, 1038, 804, 647, 638 cm−1; HRMS (ESI)
+
m/z (M + H+) calcd for C15H16NO2 242.1176, found 242.1178.
1
4,4′-Dimethoxybiphenyl-2-carboxamide (3fc). White solid;
solid: mp 50−52 °C; H NMR (400 MHz, CDCl3) δ 7.48−7.42 (m,
1
mp 118−120 °C; H NMR (400 MHz, CDCl3) δ 7.34 (d, J = 2.8
4H), 7.38−7.32 (m, 1H), 7.19−7.12 (m, 2H), 6.84 (td, J = 7.4, 1.2 Hz,
1H), 6.77 (dd, J = 7.6, 0.8 Hz, 1H), 3.76 (bs, 2H).
Hz, 1H), 7.33 (d, J = 8.8 Hz, 2H), 7.25 (d, J = 8.4 Hz, 1H), 7.03 (dd, J
= 8.4, 2.8 Hz, 1H), 6.95 (d, J = 8.8 Hz, 2H), 5.50 (bs, 1H), 5.27 (bs,
1H), 3.87 (s, 3H), 3.84 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 171.2, 159.4, 158.9, 135.2, 132.4, 132.2, 131.8, 130.2 (2C), 117.3,
114.3 (2C), 113.7, 55.7, 55.4; IR (KBr) ν 3385, 3171, 1643, 1608,
1490, 1429, 1245, 1175, 1038, 823, 612 cm−1; HRMS (ESI) m/z calcd
Synthesis of 9-Fluorenone (8aa).9d Product 8aa was obtained
by adapting the reported process.26 The mixture of 3aa (49.3 mg, 0.25
mmol) in 2.5 mL of 60% (v/v) sulfuric acid was heated with stirring at
140 °C for 36 h. After being cooled to room temperature, the reaction
mixture was quenched with water and extracted with diethyl ether
(10 mL × 3). The solvent was removed under vacuum, and the
residual was separated on a silica gel column with petroleum ether/
ethyl acetate 6/1 as the eluent to give 8aa (39.0 mg, 87%) as a yellow
solid: mp 83−85 °C; 1H NMR (400 MHz, CDCl3) δ 7.68−7.65
+
for C15H16NO3 258.1125, found 258.1131.
3′,4-Dimethoxybiphenyl-2-carboxamide (3fd). White solid;
mp 120−122 °C; 1H NMR (400 MHz, CDCl3) δ 7.35 (d, J = 2.8 Hz,
1H), 7.32 (dd, J = 8.2, 7.5 Hz, 2H), 7.27 (d, J = 8.5 Hz, 1H), 7.03 (dd,
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Article
(m, 2H), 7.54−7.51 (m, 2H), 7.49 (td, J = 7.4, 1.2 Hz, 2H), 7.30 (td,
J = 7.2, 1.2 Hz, 2H).
(5) For selected examples, see: (a) Dick, A. R.; Hull, K. L.; Sanford,
M. S. J. Am. Chem. Soc. 2004, 126, 2300. (b) Kalyani, D.; Sanford,
M. S. Org. Lett. 2005, 7, 4149. (c) Kalyani, D.; Deprez, N. R.; Desai,
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ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectra of products 3aa−ka, 3ab−ae, 3bb−bd, 3cb−cd,
3fb−fd, and 4aa−8aa. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
́
(k) Zhao, X.; Dimitrijevic, E.; Dong, V. M. J. Am. Chem. Soc. 2009,
131, 3466. (l) Kim, J.; Chang, S. J. Am. Chem. Soc. 2010, 132, 10272.
(m) Wang, X.; Truesdale, L.; Yu, J.-Q. J. Am. Chem. Soc. 2010, 132,
3648.
*E-mail: gwang@ustc.edu.cn.
Notes
The authors declare no competing financial interest.
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Pivsa-Art, S.; Nomura, M. J. Org. Chem. 1998, 63, 5211. (b) Giri, R.;
Maugel, N.; Li, J.-J.; Wang, D.-H.; Breazzano, S. P.; Saunders, L. B.;
Yu, J.-Q. J. Am. Chem. Soc. 2007, 129, 3510. (c) Wang, D.-H.; Mei,
T.-S.; Yu, J.-Q. J. Am. Chem. Soc. 2008, 130, 17676. (d) Giri, R.; Yu,
J.-Q. J. Am. Chem. Soc. 2008, 130, 14082. (e) Mei, T.-S.; Giri, R.;
Maugel, N.; Yu, J.-Q. Angew. Chem., Int. Ed. 2008, 47, 5215. (f) Zhang,
Y.-H.; Yu, J.-Q. J. Am. Chem. Soc. 2009, 131, 14654. (g) Engle, K. M.;
Wang, D.-H.; Yu, J.-Q. Angew. Chem., Int. Ed. 2010, 49, 6169.
(h) Wang, D.-H.; Engle, K. M.; Shi, B.-F.; Yu, J.-Q. Science 2010, 327,
315. (i) Shi, B.-F.; Zhang, Y.-H.; Lam, J. K.; Wang, D.-H.; Yu, J.-Q.
J. Am. Chem. Soc. 2010, 132, 460.
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J.-G.; Li, J.-J.; Wang, D.-H.; Chen, X.; Naggar, I. C.; Guo, C.;
Foxman, B. M.; Yu, J.-Q. Angew. Chem., Int. Ed. 2005, 44, 7420.
(b) Giri, R.; Chen, X.; Yu, J.-Q. Angew. Chem., Int. Ed. 2005, 44, 2112.
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ACKNOWLEDGMENTS
■
We are grateful for financial support from National Natural
Science Foundation of China (Nos. 91021004), National Basic
Research Program of China (2011CB921402).
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