N-Heterocyclic Carbene-Palladium(II)-1-Methylimidazole Complex Catalyzed Direct C-H Bond Arylation of Benzo[b]furans with Aryl Chlorides

Article abstract of DOI:10.1021/acs.joc.5b01544

The first example of sole direct C-H bond arylation of benzo[b]furans with aryl chlorides was achieved catalyzed by a well-defined NHC-Pd(II)-Im complex. Under the suitable conditions, all reactions involving kinds of benzo[b]furans and (hetero)aryl chlor

Full text of DOI:10.1021/acs.joc.5b01544

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Note
N-Heterocyclic Carbene-Palladium(II)-1-Methylimidazole Complex
Catalyzed Direct C-H Bond Arylation of Benzo[b]furans with Aryl Chlorides
Shun-Chao Yin, Quan Zhou, Xiao-Yun Zhao, and Li-Xiong Shao
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b01544 • Publication Date (Web): 14 Aug 2015
Downloaded from http://pubs.acs.org on August 19, 2015
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The Journal of Organic Chemistry
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NꢀHeterocyclic CarbeneꢀPalladium(II)ꢀ1ꢀMethylimidazole Complex
Catalyzed Direct CꢀH Bond Arylation of Benzo[b]furans with Aryl
Chlorides
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Shun-Chao Yin, Quan Zhou, Xiao-Yun Zhao and Li-Xiong Shao*
College of Chemistry and Materials Engineering, Wenzhou University, Chashan University Town,
Wenzhou, Zhejiang Province 325035, People’s Republic of China.
AUTHOR EMAIL ADDRESS Shaolix@wzu.edu.cn
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
CORRESPONDING AUTHOR FOOTNOTE: LiꢀXiong Shao, Fax: 86ꢀ577ꢀ86689300.
Shaolix@wzu.edu.cn
ABSTRACT: The first example of sole direct CꢀH bond arylation of benzo[b]furans with aryl chlorides
was achieved catalyzed by a wellꢀdefined NHCꢀPd(II)ꢀIm complex. Under the suitable conditions, all
reactions involving kinds of benzo[b]furans and (hetero)aryl chlorides proceeded well to give the
desired C2ꢀarylated benzo[b]furans in sole regioselectivity in acceptable to high yields, providing an
efficient and economic pathway for the direct C2ꢀH bond arylation of benzo[b]furans.
KEYWORDS: Nꢀheterocyclic carbeneꢀpalladium complex; CꢀH bond arylation; benzo[b]furans; aryl
chlorides; synthetic method
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2ꢀAryl benzo[b]furans are very important backbones in organic chemistry and many of their
derivatives possess medicinal and biological activities.1 Consequently, to develop efficient strategy for
the synthesis of 2ꢀaryl benzo[b]furans is of great importance. Classical method for the synthesis of such
compounds is the cyclization strategy (including the couplingꢀcyclization processes).2 In addition, as a
complement, some examples on the transition metal catalyzed crossꢀcoupling reactions of aryl halides
with furyl metal reagents or furyl halides with aryl metal reagents were also reported.3 During the past
years, the direct CꢀH bond functionalization of aryl (pseudo)halides with heteroaromatic compounds,
which at least avoids preꢀfunctionalization in one of the starting materials, has attracted much attention
for the functionalization of hetereoaromatic compounds.4 Despite the great growth in such area, however,
the direct CꢀH bond arylation of benzo[b]furans seems to be ignored. It was reported that compared to
other fiveꢀmembered heteroaromatic compounds such as furans and (benzo)thiophenes, the C2ꢀC3 bond
on benzo[b]furans seems more like a localized olefinic double bond rather than an aromatic system.5 As
a result, the sole direct CꢀH bond arylation of benzo[b]furans on the C2 or C3 position became more
challenge, usually giving the mixture of C2, C3 and the biꢀarylated benzo[b]furans in the same system.6
Due to the above reasons, in sharp contrast to the abundant papers on the direct CꢀH bond arylation of
furans and (benzo)thiophenes,7 only a handful of examples on the direct CꢀH bond arylation of
benzo[b]furans was reported to date by Ohta,8 Correia,9 DeBoef,10 Schnürch,11 and others.12 For
example, Ohta8 and Schnürch11 used the active aryl bromides as the arylating reagents in such
transformation. Aryldiazonium salts were used as the arylating reagents in Correia’s method.9 DeBoef
developed the most desirable CꢀH bond arylation of benzo[b]furans using arenes as the arylating
reagents.10 However, some problems, such as lack of regioselectivity, large excess of arenes required,
and at least a stoichiometric oxidant necessary, decreased the efficiency of such methodology. In
addition, examples on the direct CꢀH bond arylation of benzo[b]furans with chlorobenzene via benzyne
intermediate were also reported by Daugulis.13 However, because of the high activity of the benzyne
intermediate, the regioselectivity was the fatal shortcoming, and no other aryl chlorides were tested in
Daugulis’ works. Therefore, to the best of our knowledge, the direct CꢀH bond arylation of
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The Journal of Organic Chemistry
benzo[b]furans on the C2 position with sole selectivity, especially using the inexpensive and easily
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available while less active aryl chlorides as the arylating reagents, was far from well developed.
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In 2011, a wellꢀdefined Nꢀheterocyclic carbeneꢀpalladium(II)ꢀ1ꢀmethylimidazole [NHCꢀPd(II)ꢀIm]
complex 1 was developed by our group, and during the past years, it has been proven a good catalyst in
activating aryl chlorides toward CꢀC and CꢀN coupling reactions.14 Furthermore, it was also found to be
an efficient catalyst in the direct CꢀH bond arylation of (benzo)oxazoles, (benz)imidazoles and fluorenes
with aryl chlorides.15 Based on the previous studies, it can be postulated that the highly active NHCꢀ
Pd(II)ꢀIm complex may be an efficient catalyst to activate aryl chlorides toward the direct sole C2ꢀH
bond arylation of benzo[b]furans. Therefore, prompted by our successful experiences on the above
reactions, we then turned our interest to the challengingly direct CꢀH bond arylation of benzo[b]furans
with aryl chlorides in sole C2ꢀselectivity. Herein, we report our efforts on the direct C2ꢀH bond arylation
of various benzo[b]furans with kinds of (hetero)aryl chlorides catalyzed by NHCꢀPd(II)ꢀIm complex 1 in
detail.
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The reaction conditions were first optimized by using the model reaction of benzo[b]furan 2a (1.0
mmol) with chlorobenzene 3a (0.5 mmol) in the presence of NHCꢀPd(II)ꢀIm complex 1 (5.0 mol%) in
toluene (2.0 mL) at 130 oC for 12 h to evaluate various bases (2.5 equiv). Some representative results are
shown in Table 1. Among the bases screened (Table 1, entries 1ꢀ4), KOtBu gave the best yield of 42%
(Table 1, entry 1). In the presence of other bases such as NaOtBu, NaOH and KOH, very low yields of
the corresponding product 4a were observed (Table 1, entries 2ꢀ4). In addition, no reaction occurred
.
using other bases such as LiOtBu, Li2CO3, Na2CO3, K2CO3, Cs2CO3, K3PO4 3H2O, NaHCO3 and KOAc.
The yield remained unchanged using KOtBu as the base even if the reaction time was prolonged to 24 h.
When the amount of KOtBu was decreased to 1.2 equiv, similar yield of product 4a was observed (Table
1, entry 5 vs entry 1), while that of KOtBu was further decreased to 1.0 equiv, the yield slightly
decreased to 37% (Table 1, entry 6 vs entry 1). Then a variety of solvents was tested in the presence of
1.2 equiv KOtBu. For example, when THF was chosen as the solvent, product 4a was obtained in 52%
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yield (Table 1, entry 7). However, using other solvents such as DMSO, CH3CN and DMF, no reaction
occurred. Considering that in the transition metal catalyzed direct CꢀH bond functionalization of
heteroaromatic compounds, additives are usually proposed to enhance the reactions to some extent.
Therefore, a series of copper salts was first examined, and it was found that copper salts can indeed
affect the reaction (Table 1, entries 8ꢀ14). For example, all copper salts besides CuBr can promote this
reaction to give higher yields, and the best result was achieved using Cu2O as the additive (Table 1,
entry 11).16 It was noted here that the best 77% yield may be due to the incomplete conversion. For
example, only the starting benzo[b]furan 2a and product 4a were detected by GCꢀMS, implying that no
side reaction occurred. In addition, the yield almost kept untouched even if the reaction time was
prolonged to 18 h. In addition, compared to Cu2O, inferior results were observed using other additives
such as PivOH (48%), PivONa (51%), AgOAc (44%) and Ag2CO3 (43%).17 Using Cu2O (10.0 mol%) as
the catalyst in the absence of NHCꢀPd(II)ꢀIm complex 1, no reaction occurred. Finally, it is worthy of
noting here that in all the above reactions, only the C2ꢀarylated product 4a was obtained, and no C3ꢀ
arylated byꢀproduct was detected in any cases.
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Table 1. Optimization for the Complex 1 Catalyzed Reaction of
Benzo[b]furan 2a with Chlorobenzene 3a.
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5
6
7
Cl
NHC-Pd(II)-Im 1
(5.0 mol%)
+
base, solvent
O
O
4a
130 oC, 12 h
2a
3a
8
9
Pri
Pri
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Cl
Pd
Cl
N
N
NHC-Pd(II)-Im 1:
Pri
N
N
Pri
entrya
1
base (equiv)
KOtBu (2.5)
solvent
toulene
toulene
additive yield (%)
42
<5
<5
7
NaOtBu (2.5)
NaOH (2.5)
KOH (2.5)
2
3
toulene
toulene
toulene
toulene
THF
4
KOtBu (1.2)
KOtBu (1.0)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
KOtBu (1.2)
5
44
37
52
6
7
8
THF
CuCl
CuI
64
69
50
77
69
58
58
9
THF
10
11
12
13
14
THF
CuBr
Cu2O
THF
THF
CuO
CuBr2
THF
Cu(OAc)2
THF
aAll reactions were carried out using 2a (1.0 mmol), 3a (0.5
mmol), 1 (5.0 mol%), additive (0 or 10.0 mol%), base (1.0-2.5
equiv) in solvent (2.0 mL) at 130 oC for 12 h.
With the optimal conditions established, the scope and limitation of this reaction was first examined
by using a number of aryl chlorides 3 and benzo[b]furan 2a (Table 2). As can be seen from Table 2,
substituents on the aryl chlorides 3 had some effect on the reactions. For example, aryl chlorides 3
having electronꢀdonating substituents such as methoxy and methyl groups were better substrates than
that having electronꢀwithdrawing group such as fluorine atom, giving superior yields under identical
conditions (Table 2, entries 1ꢀ6 vs 7 and 8). Sterically hindered substituents on the aryl chlorides 3 did
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not affect the reactions significantly to give the corresponding products 4d and 4g in good yields,
respectively (Table 2, entries 3 and 6). The vinyl group on the aryl chloride 3j kept untouched in such
transformation to give the desired arylated product 4j in 75% yield (Table 2, entry 9). Heteroaryl
chlorides such as 3ꢀchloropyridine 3k and its analogue, 2ꢀchloropyridine 3l, were also suitable substrates
in the presence of elevated amount of KOtBu (2.5 equiv) to give the corresponding products 4k and 4l in
77% and 54% yields, respectively (Table 2, entries 11 and 13).
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Table 2. NHC-Pd(II)-Im Complex 1 Catalyzed Reactions of
Benzo[b]furan 2a with Aryl Chlorides 3.
Cl
NHC-Pd(II)-Im 1
(5.0 mol%)
+
Cu2O (10.0 mol%)
O
O
4
R'
t
o
R'
KO Bu, THF, 130 C
12 h
2a
3
entrya
3 (R')
yield (%)
4b, 81
4c, 78
4d, 76
4e, 74
4f, 77
4g, 69
4h, 65
4i, 60
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3
4
5
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7
8
9
3b (4-OMe)
3c (3-OMe)
3d (2-OMe)
3e (4-Me)
3f (3-Me)
3g (2-Me)
3h (4-F)
3i (3-F)
3j (4-vinyl)
4j, 75
Cl
10
4k, 47
4k, 77
3k
N
11b
3k
3l
4l, 36
4l, 54
12
N
Cl
13b
3l
aOtherwise specified, all reactions were carried out using 2a (1.0
mmol), 3 (0.5 mmol), 1 (5.0 mol%), Cu2O (10.0 mol%), KOtBu (1.2
equiv) in THF (2.0 mL) at 130 oC for 12 h.
bKOtBu (2.5 equiv) was added.
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The Journal of Organic Chemistry
Encouraged by the above successful results, the reactions of a variety of benzo[b]furans 2 with aryl
1
2
chlorides 3 were then investigated under the optimal conditions (Table 3). All reactions worked
smoothly to give the desired C2ꢀarylated products 4 in moderate to good yields. Substituents such as
electronꢀdonating, ꢀwithdrawing and sterically hindered ones on both substrates did not affect the
reactions significantly. For instance, both 7ꢀmethylbenzo[b]furan 2c and 7ꢀfluorobenzo[b]furan 2e
having sterically hindered substituent were suitable substrates to give the desired C2ꢀarylated products
in moderate to good yields (Table 3, entries 7ꢀ11, 14 and 15). Sterically hindered 2ꢀmethylphenyl
chloride 3g was also a good substrate to afford the corresponding products 4p and 4v in 75% and 72%
yields, respectively (Table 3, entries 4 and 10). The reaction involving strongly electronꢀwithdrawing 5ꢀ
CF3 substituted 2f also worked well to give product 4ab in 69% yield (Table 3, entry 16).
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Table 3. NHC-Pd(II)-Im Complex 1 Catalyzed Reactions of
Benzo[b]furans 2 with Aryl Chlorides 3.
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2
3
4
5
6
7
8
Cl
NHC-Pd(II)-Im 1
(5.0 mol%)
+
Cu2O (10.0 mol%)
KOtBu, THF
130 oC, 12 h
O
4
R'
O
R
R
R'
3
2
9
entrya
1
2 (R)
3 (R')
yield (%)
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12
13
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2b
2b
2b
2b
2b
2b
2c
2c
2c
2c
2c
2d
2d
(5-Me)
3a
3e
3f
(H)
4m
, 83
, 76
, 72
2
4n
4o
(4-Me)
(3-Me)
3
4
3g (2-Me)
3h (4-F)
4p, 75
4q, 71
5
6
3j
4r
, 80
(4-vinyl)
7
3a
3e
3f
4s
, 73
(7-Me)
(5-F)
8
4t
, 80
9
4u, 73
4v, 72
10
11
12
13
14
15
16
3g
3j
4w
, 68
3a
4x, 76
4y, 82
4z, 62
3b (4-OMe)
2e (7-F)
2e
3a
3e
3e
4aa, 83
2f (5-CF3)
4ab, 69
aAll reactions were carried out using 2 (1.0 mmol), 3 (0.5 mmol),
1 (5.0 mol%), Cu2O (10.0 mol%), KOtBu (1.2 equiv) in THF (2.0
mL) at 130 oC for 12 h.
In conclusion, the first example of NHCꢀPd(II) complex catalyzed sole direct C2ꢀH bond arylation of
benzo[b]furans with aryl chlorides was reported in this paper. Under the optimal conditions, various
benzo[b]furans can be arylated solely in the C2ꢀposition with (hetero)aryl chlorides catalyzed by NHCꢀ
Pd(II)ꢀIm complex 1. In addition, various substituents such as electronꢀdonating, ꢀneutral, ꢀwithdrawing
and sterically hindered ones on both substrates can be tolerated, affording a novel and efficient
methodology for the direct C2ꢀH bond arylation of benzo[b]furans with economic and easily available
aryl chlorides.
Experimental section
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General Remarks. Melting points are uncorrected. NMR spectra were recorded at 500 (for 1H NMR)
1
2
13
1
13
or 125 MHz (for C NMR), respectively. H NMR and C NMR spectra recorded in CDCl3 solutions
were referenced to TMS (0.00 ppm) and the residual solvent peak (77.0 ppm), respectively. Jꢀvalues are
in Hz. Organic solvents used were dried by standard methods. The mass analyzer type for the high
resolution mass spectra (HRMS, ESI) is quadrupole. Other commercially obtained reagents were used
without further purification. Flash column chromatography was performed on silica gel.
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General Procedure for the NHC-Pd(II)-Im Complex 1 Catalyzed Direct C-H Bond Arylation of
Benzo[b]furans 2 with Aryl Chlorides 3. Under N2 atmosphere, KOtBu (67.3 mg, 0.6 mmol, 1.2 equiv),
Cu2O (7.2 mg, 0.05 mmol, 10.0 mol%), NHCꢀPd(II)ꢀIm complex 1 (16.0 mg, 0.025 mmol, 5.0 mol%),
THF (2.0 mL), benzo[b]furans 2 (2.0 equiv) and aryl chlorides 3 (0.5 mmol) were successively added
into a sealed tube. The mixture was stirred vigorously at 130 oC for 12 h. Then the solvent was removed
under reduced pressure and the residue was purified by flash column chromatography (eluent: petroleum
ether) to give the pure products 4.
o
o
1
Compound 4a: white solid (74.7 mg, 77%); mp: 120ꢀ121 C (lit.18 120ꢀ121 C); H NMR (CDCl3,
500 MHz, TMS) δ 7.87 (dd, J = 8.0, 1.0 Hz, 2H), 7.59 (d, J = 8.0 Hz, 1H), 7.53 (d, J = 8.0 Hz, 1H), 7.45
(t, J = 8.0 Hz, 2H), 7.37ꢀ7.34 (m, 1H), 7.28 (td, J = 8.0, 1.0 Hz, 1H), 7.23 (td, J = 7.5, 1.0 Hz, 1H), 7.03
(s, 1H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.9, 154.9, 130.5, 129.2, 128.8, 128.5, 124.9, 124.2,
122.9, 120.9, 111.2, 101.3.
o
o
1
Compound 4b: white solid (90.8 mg, 81%); mp: 148ꢀ149 C (lit.2p 148ꢀ150 C); H NMR (CDCl3,
500 MHz, TMS) δ 7.80 (dt, J = 9.5, 3.0 Hz, 2H), 7.56ꢀ7.54 (m, 1H), 7.51ꢀ7.49 (m, 1H), 7.25 (td, J = 8.5,
1.5 Hz, 1H), 7.21 (td, J = 7.0, 1.0 Hz, 1H), 6.98 (dt, J = 5.0, 2.0 Hz, 2H), 6.88 (d, J = 0.5 Hz, 1H), 3.86
(s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 160.0, 156.1, 154.7, 129.5, 126.4, 123.7, 123.4, 122.8,
120.6, 114.3, 111.0, 99.7, 55.4.
o
o
1
Compound 4c: white solid (87.4 mg, 78%); mp: 51ꢀ52 C (lit.19 51ꢀ53 C); H NMR (CDCl3, 500
MHz, TMS) δ 7.57 (d, J = 8.5 Hz, 1H), 7.52 (d, J = 8.0 Hz, 1H), 7.45 (dt, J = 8.0, 1.0 Hz, 1H), 7.41 (t, J
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= 2.5 Hz, 1H), 7.34 (t, J = 8.0 Hz, 1H), 7.28 (td, J = 8.0, 1.0 Hz, 1H), 7.22 (td, J = 8.0, 1.0 Hz, 1H), 7.01
(d, J = 0.5 Hz, 1H), 6.90 (ddd, J = 8.5, 2.5, 1.0 Hz, 1H), 3.88 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz)
δ 160.0, 155.8, 154.9, 131.8, 129.8, 129.2, 124.3, 122.9, 120.9, 117.6, 114.5, 111.2, 110.2, 101.6, 55.3.
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Compound 4d: white solid (85.2 mg, 76%); mp: 79ꢀ80 C (lit.20 79ꢀ80 C); H NMR (CDCl3, 500
MHz, TMS) δ 8.06 (d, J = 8.0 Hz, 1H), 7.58 (d, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.34 (s, 1H),
7.30ꢀ7.24 (m, 2H), 7.20 (t, J = 7.5 Hz, 1H), 7.06 (t, J = 7.5 Hz, 1H), 6.96 (d, J = 8.5 Hz, 1H), 3.95 (s,
3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 156.5, 153.9, 152.2, 129.8, 129.2, 127.1, 124.1, 122.6, 121.0,
120.8, 119.4, 111.1, 110.8, 106.3, 55.4.
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Compound 4e: white solid (77.0 mg, 74%); mp: 128ꢀ129 C (lit.21 128ꢀ129 C); H NMR (CDCl3,
500 MHz, TMS) δ 7.74 (d, J = 8.0 Hz, 2H), 7.54 (d, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.27ꢀ7.19
(m, 4H), 6.93 (s, 1H), 2.37 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 156.2, 154.8, 138.5, 129.44,
129.37, 127.8, 124.9, 124.0, 122.8, 120.7, 111.1, 100.5, 21.3.
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Compound 4f: white solid (80.1 mg, 77%); mp: 75ꢀ76 oC (lit.2p 74ꢀ75 oC); 1H NMR (CDCl3, 500 MHz,
TMS) δ 7.67 (s, 1H), 7.64 (d, J = 8.0 Hz, 1H), 7.55 (d, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.31ꢀ
7.19 (m, 3H), 7.13 (d, J = 7.0 Hz, 1H), 6.96 (s, 1H), 2.39 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ
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156.1, 154.9, 138.4, 130.4, 129.4, 129.3, 128.7, 125.5, 124.2, 122.9, 122.2, 120.8, 111.1, 101.2, 21.5.
Compound 4g3d: colorless liquid (71.8 mg, 69%); H NMR (CDCl3, 500 MHz, TMS) δ 7.83 (d, J =
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7.0 Hz, 1H), 7.57 (dd, J = 7.5, 0.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.28ꢀ7.24 (m, 4H), 7.21 (td, J =
7.5, 0.5 Hz, 1H), 6.85 (s, 1H), 2.55 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ 155.6, 154.4, 135.8,
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131.2, 129.9, 129.2, 128.5, 128.1, 126.1, 124.2, 122.8, 120.9, 111.1, 105.1, 21.9.
Compound 4h: white solid (68.9 mg, 65%); mp: 120ꢀ121 C (lit.2p 120ꢀ122 C); H NMR (CDCl3,
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500 MHz, TMS) δ 7.84ꢀ7.81 (m, 2H), 7.56 (d, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.28 (t, J = 7.5
Hz, 1H), 7.22 (t, J = 7.5 Hz, 1H), 7.13 (t, J = 8.5 Hz, 2H), 6.94 (s, 1H); C{1H} NMR (CDCl3, 125
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MHz) δ 162.9 (d, JCꢀF = 247.25 Hz), 155.0 (d, JCꢀF = 19.75 Hz), 129.2, 126.8 (d, J = 8.125 Hz), 124.3,
123.0, 120.9, 115.9 (d, JCꢀF = 21.875 Hz), 111.1, 101.0 (d, J = 1.5 Hz).
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Compound 4i: white solid (63.6 mg, 60%); mp: 77ꢀ78 C (lit.2o 77ꢀ78 C); H NMR (CDCl3, 500
MHz, TMS) δ 7.61 (d, J = 8.0 Hz, 1H), 7.57 (d, J = 7.5 Hz, 1H), 7.54 (dt, J =10.0, 2.0 Hz, 1H), 7.51 (d,
J = 8.5 Hz, 1H), 7.38 (td, J = 8.0, 6.0 Hz, 1H), 7.29 (td, J = 8.0, 1.0 Hz, 1H), 7.23 (t, J = 7.5 Hz, 1H),
7.04ꢀ7.00 (m, 2H); 13C{1H} NMR (CDCl3, 125 MHz) δ 163.2 (d, JCꢀF = 244.25 Hz), 154.9, 154.6 (d, J =
3.0 Hz), 132.6 (d, J = 8.375 Hz), 130.4 (d, J = 8.375 Hz), 129.0, 124.7, 123.1, 121.1, 120.6 (d, J = 2.875
Hz), 115.3 (d, J = 21.25 Hz), 111.8 (d, J = 23.375 Hz), 111.2, 102.3.
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Compound 4j: white solid (82.5 mg, 75%); mp: 168ꢀ169 °C; H NMR (CDCl3, 500 MHz, TMS) δ
7.80 (d, J = 8.0 Hz, 2H), 7.55 (d, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.45 (d, J = 8.0 Hz, 2H),
7.26 (td, J = 8.0, 1.0 Hz, 1H), 7.21 (t, J = 7.5 Hz, 1H), 6.98 (s, 1H), 6.72 (dd, J = 18.0, 10.5 Hz, 1H),
5.79 (d, J = 18.0 Hz, 1H), 5.28 (d, J = 10.5 Hz, 1H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.7, 154.9,
137.7, 136.3, 129.7, 129.2, 126.6, 125.0, 124.3, 122.9, 120.9, 114.4, 111.1, 101.4; MS (ESI): 221
[M+H]+; HRMS (ESI) calcd for C16H13O [M+H]+: 221.0961; found: 221.0952; IR (neat) ν 3044, 1624,
1604, 1576, 1497, 1450, 1407, 1348, 1259, 1166, 1112, 1104, 1034, 1011, 990, 930, 906, 882, 845, 803,
747, 738 cmꢀ1.
Compound 4k22: yellow solid (75.1 mg, 77%); mp: 79ꢀ80 C; H NMR (CDCl3, 500 MHz, TMS) δ
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9.10 (s, 1H), 8.56 (dd, J = 4.5, 1.0 Hz, 1H), 8.10ꢀ8.07 (m, 1H), 7.59 (d, J = 8.0 Hz, 1H), 7.52 (d, J = 8.0
Hz, 1H), 7.35ꢀ7.29 (m, 2H), 7.24 (t, J = 7.5 Hz, 1H), 7.08 (d, J = 2.0 Hz, 1H); C{1H} NMR (CDCl3,
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125 MHz) δ 155.1, 152.9, 149.2, 146.4, 131.8, 128.7, 126.6, 124.9, 123.5, 123.2, 121.1, 111.2, 102.7.
Compound 4l: yellow solid (52.7 mg, 54%); mp: 84ꢀ85 C (lit.23 80ꢀ81 C); H NMR (500 MHz,
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CDCl3) δ 8.67 (d, J = 4.5 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.76 (t, J = 7.5 Hz, 1H), 7.64 (d, J = 7.5 Hz,
1H), 7.56 (d, J = 8.0 Hz, 1H), 7.43 (s, 1H), 7.33 (t, J = 7.5 Hz, 1H), 7.27ꢀ7.21 (m, 2H); C{1H} NMR
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(CDCl3, 125 MHz) δ 155.3, 155.1, 149.9, 149.3, 136.7, 128.9, 125.2, 123.2, 122.8, 121.7, 119.8, 111.5,
104.8.
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Compound 4m: white solid (86.3 mg, 83%); mp: 129ꢀ130 C (lit.2p 131ꢀ133 C); H NMR (CDCl3,
500 MHz, TMS) δ 7.83 (d, J = 7.5 Hz, 2H), 7.43ꢀ7.37 (m, 3H), 7.32 (d, J = 7.5 Hz, 2H), 7.07 (d, J = 8.0
Hz, 1H), 6.91 (s, 1H), 2.42 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 156.0, 153.4, 132.3, 130.7,
129.3, 128.7, 128.4, 125.5, 124.9, 120.7, 110.6, 101.1, 21.3.
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Compound 4n: white solid (84.4 mg, 76%); mp: 140ꢀ141 °C; 1H NMR (CDCl3, 500 MHz, TMS) δ
7.73 (d, J = 8.0 Hz, 2H), 7.37 (d, J = 8.5 Hz, 1H), 7.33 (s, 1H), 7.24ꢀ7.22 (m, 2H), 7.06 (d, J = 8.5 Hz,
1H), 6.87 (s, 1H), 2.43 (s, 3H), 2.38 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ 156.3, 153.3, 138.4,
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132.2, 129.47, 129.44, 128.0, 125.2, 124.8, 120.6, 110.6, 100.3, 21.32, 21.30; MS (ESI): 223 [M+H]+;
HRMS (ESI) calcd for C16H15O [M+H]+: 223.1117; found: 223.1122; IR (neat) ν 3014, 2908, 2842,
1501, 1461, 1375, 1328, 1275, 1262, 1209, 1196, 1133, 1113, 1036, 1013, 914, 879, 821, 798, 743 cmꢀ1.
Compound 4o: white solid (80.0 mg, 72%); mp: 78ꢀ79 °C; 1H NMR (CDCl3, 500 MHz, TMS) δ 7.67
(s, 1H), 7.64 (d, J = 7.5 Hz, 1H), 7.39 (d, J = 8.5 Hz, 1H), 7.34 (s, 1H), 7.31 (t, J = 7.5 Hz, 1H), 7.14 (d,
J = 7.5 Hz, 1H), 7.07 (d, J = 8.5 Hz, 1H), 6.92 (s, 1H), 2.43 (s, 3H), 2.41 (s, 3H); 13C{1H} NMR (CDCl3,
125 MHz) δ 156.2, 153.4, 138.4, 132.3, 130.6, 129.4, 129.2, 128.7, 125.5, 125.4, 122.1, 120.7, 110.6,
101.0, 21.5, 21.3; MS (ESI): 223 [M+H]+; HRMS (ESI) calcd for C16H15O [M+H]+: 223.1117; found:
223.1113; IR (neat) ν 2928, 2855, 1610, 1560, 1457, 1328, 1265, 1199, 1133, 1050, 925, 884, 853, 814,
801, 783, 740, 692 cmꢀ1.
Compound 4p: colorless liquid (83.3 mg, 75%); 1H NMR (CDCl3, 500 MHz, TMS) δ 7.82 (d, J = 7.0
Hz, 1H), 7.38 (d, J = 8.0 Hz, 1H), 7.35 (s, 1H), 7.29ꢀ7.22 (m, 3H), 7.07 (d, J = 8.0 Hz, 1H), 6.78 (s, 1H),
2.54 (s, 3H), 2.43 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.7, 152.8, 135.7, 132.1, 131.2, 130.0,
129.3, 128.3, 128.0, 126.0, 125.5, 120.7, 110.5, 104.8, 21.9, 21.3. MS (ESI): 223 [M+H]+; HRMS (ESI)
calcd for C16H15O [M+H]+: 223.1117; found: 223.1115; IR (neat) ν 3014, 2961, 2921, 2855, 1618, 1601,
1590, 1573, 1472, 1461, 1379, 1329, 1270, 1194, 1129, 1020, 914, 869, 830, 799, 760, 738, 719 cmꢀ1.
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Compound 4q2r: white solid (80.3 mg, 71%); mp: 161ꢀ162 C; H NMR (CDCl3, 500 MHz, TMS) δ
7.82ꢀ7.78 (m, 2H), 7.37 (d, J = 8.0 Hz, 1H), 7.34 (s, 1H), 7.14ꢀ7.07 (m, 3H), 6.86 (s, 1H), 2.43 (s, 3H);
13C{1H} NMR (CDCl3, 125 MHz) δ 162.8 (d, JCꢀF = 247.0 Hz), 155.1, 153.3, 132.4, 129.3, 127.0 (d, JCꢀ
F = 3.125 Hz), 126.7 (d, JCꢀF = 8.125 Hz), 125.5, 120.7, 115.8 (d, JCꢀF = 21.875 Hz), 110.6, 100.8 (d, J =
1.625 Hz), 21.3.
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Compound 4r: white solid (93.6 mg, 80%); mp: 168ꢀ169 °C; H NMR (CDCl3, 500 MHz, TMS) δ
7.77 (d, J = 8.0 Hz, 2H), 7.44 (d, J = 8.0 Hz, 2H), 7.37 (d, J = 8.5 Hz, 1H), 7.31 (s, 1H), 7.06 (d, J = 8.0
Hz, 1H), 6.89 (s, 1H), 6.71 (dd, J = 18.0, 10.5 Hz, 1H), 5.78 (d, J = 18.0 Hz, 1H), 5.27 (d, J = 10.5 Hz,
1H), 2.42 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.7, 153.3, 137.6, 136.3, 132.3, 129.9, 129.3,
126.6, 125.6, 124.9, 120.7, 114.3, 110.6, 101.2, 21.3; MS (ESI): 235 [M+H]+; HRMS (ESI) calcd for
C17H15O [M+H]+: 235.1117; found: 235.1124; IR (neat) ν 3083, 2920, 2847, 1627, 1607, 1582, 1506,
1464, 1405, 1379, 1334, 1261, 1197, 1115, 1039, 989, 913, 900, 845, 802, 741 cmꢀ1.
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Compound 4s24: colorless liquid (75.9 mg, 73%); H NMR (CDCl3, 500 MHz, TMS) δ 7.84 (d, J =
7.5 Hz, 2H), 7.41ꢀ7.36 (m, 3H), 7.30 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.5 Hz, 1H), 7.05 (d, J = 7.0 Hz,
1H), 6.95 (s, 1H), 2.56 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.5, 153.9, 130.7, 128.70, 128.65,
128.4, 125.2, 124.8, 122.9, 121.4, 118.3, 101.6, 15.0.
Compound 4t: colorless liquid (88.8 mg, 80%); 1H NMR (CDCl3, 500 MHz, TMS) δ 7.73 (d, J = 8.0
Hz, 2H), 7.36 (d, J = 7.5 Hz, 1H), 7.20 (d, J = 8.0 Hz, 2H), 7.10 (t, J = 7.5 Hz, 1H), 7.03 (d, J = 7.0 Hz,
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1H), 6.89 (s, 1H), 2.56 (s, 3H), 2.35 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ 155.8, 153.8, 138.4,
129.4, 128.8, 128.0, 124.9, 124.8, 122.9, 121.3, 118.2, 100.8, 21.3, 15.0; MS (ESI): 223 [M+H]+;
HRMS (ESI) calcd for C16H15O [M+H]+: 223.1117; found: 223.1110; IR (neat) ν 3055, 3021, 2914,
1506, 1483, 1452, 1416, 1351, 1292, 1202, 1174, 1160, 1031, 1014, 911, 857, 821, 809, 802, 765, 741
cmꢀ1.
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Compound 4u: colorless liquid (81.0 mg, 73%); H NMR (CDCl3, 500 MHz, TMS) δ 7.68ꢀ7.65 (m,
2H), 7.38 (d, J = 7.5 Hz, 1H), 7.31 (t, J = 7.5 Hz, 1H), 7.14 (d, J = 8.0 Hz, 1H), 7.10 (d, J = 7.5 Hz, 1H),
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7.06 (d, J = 7.5 Hz, 1H), 6.96 (s, 1H), 2.58 (s, 3H), 2.41 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ
155.7, 153.9, 138.3, 130.6, 129.2, 128.7, 128.6, 125.4, 125.1, 122.9, 122.1, 121.3, 118.3, 101.4, 21.5,
15.0; MS (ESI): 223 [M+H]+; HRMS (ESI) calcd for C16H15O [M+H]+: 223.1117; found: 223.1116; IR
(neat) ν 3057, 2917, 2852, 1612, 1574, 1484, 1451, 1414, 1349, 1291, 1214, 1186, 1091, 1040, 928, 864
cmꢀ1.
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Compound 4v: colorless liquid (79.9 mg, 72%); 1H NMR (CDCl3, 500 MHz, TMS) δ 7.83 (d, J = 7.0
Hz, 1H), 7.41 (d, J = 8.0 Hz, 1H), 7.29ꢀ7.23 (m, 3H), 7.12 (t, J = 7.5 Hz, 1H), 7.07 (d, J = 7.0 Hz, 1H),
6.85 (s, 1H), 2.564 (s, 3H), 2.559 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.4, 153.5, 135.8,
131.3, 130.1, 128.6, 128.4, 128.1, 126.0, 125.1, 122.8, 121.3, 118.3, 105.2, 21.9, 15.0; MS (ESI): 223
[M+H]+; HRMS (ESI) calcd for C16H15O [M+H]+: 223.1117; found: 223.1121; IR (neat) ν 3067, 2915,
2855, 1484, 1457, 1418, 1381, 1295, 1209, 1179, 1020, 911, 856, 806, 768, 743, 717 cmꢀ1.
Compound 4w: white solid (79.6 mg, 68%); mp: 88ꢀ89 °C; 1H NMR (CDCl3, 500 MHz, TMS) δ 7.78
(d, J = 8.5 Hz, 2H), 7.43 (d, J = 8.5 Hz, 2H), 7.36 (d, J = 7.5 Hz, 1H), 7.10 (t, J = 7.5 Hz, 1H), 7.05 (d, J
= 7.0 Hz, 1H), 6.94 (s, 1H), 6.71 (dd, J = 17.5, 11.0 Hz, 1H), 5.77 (d, J = 17.5 Hz, 1H), 5.26 (d, J = 11.0
Hz, 1H), 2.56 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 155.3, 153.9, 137.6, 136.3, 130.0, 128.7,
126.6, 125.2, 125.0, 123.0, 121.4, 118.3, 114.3, 101.7, 15.0; MS (ESI): 235 [M+H]+; HRMS (ESI) calcd
for C17H15O [M+H]+: 235.1117; found: 235.1127; IR (neat) ν 2920, 2847, 1697, 1621, 1607, 1582,
1500, 1486, 1407, 1351, 1295, 1264, 1205, 1180, 1031, 1008, 990, 913, 845, 812, 771, 743 cmꢀ1.
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Compound 4x: white solid (80.6 mg, 76%); mp: 130ꢀ131 °C; H NMR (CDCl3, 500 MHz, TMS) δ
7.81 (d, J = 7.0 Hz, 2H), 7.43ꢀ7.38 (m, 3H), 7.34 (t, J = 7.5 Hz, 1H), 7.19 (dd, J = 8.5, 2.5 Hz, 1H), 6.97
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(td, J = 9.0, 2.5 Hz, 1H), 6.92 (s, 1H); C{1H} NMR (CDCl3, 125 MHz) δ 159.3 (d, JCꢀF = 236.5 Hz),
157.7, 151.1, 130.1 (d, JCꢀF = 8.25 Hz), 129.9, 128.8 (d, J = 7.375 Hz), 125.0, 111.8 (d, JCꢀF = 24.375
Hz); 111.7 (d, JCꢀF = 7.625 Hz); 106.3 (d, JCꢀF = 25.0 Hz), 101.4 (d, J = 4.0 Hz); MS (ESI): 213 [M+H]+;
HRMS (ESI) calcd for C14H10FO [M+H]+: 213.0710; found: 213.0699; IR (neat) ν 3100, 3065, 3040,
2914, 2847, 1593, 1457, 1441, 1341, 1272, 1189, 1129, 1020, 950, 915, 866, 799, 762, 741 cmꢀ1.
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Compound 4y: white solid (99.2 mg, 82%); mp: 145ꢀ146 °C; H NMR (CDCl3, 500 MHz, TMS) δ
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3H), 6.80 (d, J = 0.5 Hz, 1H), 3.83 (s, 3H); C{1H} NMR (CDCl3, 125 MHz) δ 160.2, 159.3 (d, JCꢀF
=
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236.125 Hz), 157.9, 150.9, 130.3 (d, J = 10.875 Hz), 126.5, 123.0, 114.3, 111.4 (d, JCꢀF = 9.625 Hz),
111.2 (d, JCꢀF = 26.25 Hz), 106.0 (d, JCꢀF = 25.0 Hz), 99.8 (d, JCꢀF = 3.875 Hz), 55.3; MS (ESI): 243
[M+H]+; HRMS (ESI) calcd for C15H12FO2 [M+H]+: 243.0816; found: 243.0819; IR (neat) ν 3014,
2968, 2835, 1610, 1587, 1567, 1504, 1457, 1418, 1348, 1305, 1245, 1169, 1123, 1109, 1036, 1023, 954,
914, 864, 829, 819, 809, 790, 763, 738 cmꢀ1.
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Compound 4z: white solid (65.7 mg, 62%); mp: 65ꢀ66 °C; H NMR (CDCl3, 500 MHz, TMS) δ 7.86
(d, J = 7.5 Hz, 2H), 7.44 (t, J = 8.0 Hz, 2H), 7.36 (t, J = 7.0 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H), 7.12 (td, J
= 7.5, 4.0 Hz, 1H), 7.02ꢀ6.98 (m, 2H); 13C{1H} NMR (CDCl3, 125 MHz) δ 157.0, 148.0 (d, JCꢀF
=
247.75 Hz), 141.8 (d, J = 11.125 Hz), 132.7 (d, J = 3.375 Hz), 129.8, 128.9 (d, J = 17.0 Hz), 125.1,
123.5 (d, J = 5.875 Hz), 116.5 (d, J = 3.75 Hz), 110.6 (d, J = 16.125 Hz), 101.5 (d, J = 2.25 Hz); MS
(ESI): 213 [M+H]+; HRMS (ESI) calcd for C14H10FO [M+H]+: 213.0710; found: 213.0713; IR (neat) ν
3106, 3055, 2926, 1632, 1590, 1495, 1481, 1433, 1306, 1259, 1216, 1180, 1056, 1045, 1017, 909, 879,
861, 816, 769, 755, 723 cmꢀ1.
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Compound 4aa: white solid (93.8 mg, 83%); mp: 119ꢀ120 °C; H NMR (CDCl3, 500 MHz, TMS) δ
7.72 (d, J = 8.0 Hz, 2H), 7.27 (d, J = 7.5 Hz, 1H), 7.20 (d, J = 8.0 Hz, 2H), 7.09 (td, J = 8.0, 4.5 Hz, 1H),
6.97 (dd, J = 10.5, 8.0 Hz, 1H), 6.90 (d, J = 3.0 Hz, 1H), 2.35 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz)
δ 157.3, 148.0 (d, JCꢀF = 247.375 Hz), 141.6 (d, JCꢀF = 10.875 Hz), 139.0, 132.9 (d, JCꢀF = 3.25 Hz),
129.5, 127.1, 125.0, 123.4 (d, JCꢀF = 5.875 Hz), 116.3 (d, JCꢀF = 3.75 Hz), 110.3 (d, JCꢀF = 16.125 Hz),
100.7 (d, JCꢀF = 2.0 Hz), 21.3; MS (ESI): 227 [M+H]+; HRMS (ESI) calcd for C15H12FO [M+H]+:
227.0867; found: 227.0866; IR (neat) ν 2915, 2868, 1630, 1597, 1507, 1484, 1434, 1328, 1308, 1259,
1212, 1179, 1056, 1043, 909, 864, 848, 806, 770, 723 cmꢀ1.
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Compound 4ab: white solid (95.3 mg, 69%); mp: 153ꢀ154 °C; H NMR (CDCl3, 500 MHz, TMS) δ
7.83 (s, 1H), 7.74 (d, J = 8.0 Hz, 2H), 7.55 (d, J = 8.5 Hz, 1H), 7.50 (d, J = 8.5 Hz, 1H), 7.25 (d, J = 8.0
Hz, 2H), 6.97 (s, 1H), 2.39 (s, 3H); 13C{1H} NMR (CDCl3, 125 MHz) δ 158.2, 156.1, 139.4, 129.6,
128.2 (q, JCꢀF = 303.75 Hz), 125.8, 125.6 (q, JCꢀF = 32.0 Hz), 123.6, 121.0 (q, JCꢀF = 3.5 Hz), 118.3 (q,
JCꢀF = 3.875 Hz), 111.8, 111.4, 104.4, 100.5, 21.4; MS (ESI): 277 [M+H]+; HRMS (ESI) calcd for
C16H12F3O [M+H]+: 277.0835; found: 227.0848; IR (neat) ν 3027, 2921, 2862, 1613, 1583, 1504, 1441,
1331, 1278, 1259, 1156, 1113, 1053, 927, 909, 891, 821, 791, 751 cmꢀ1.
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ACKNOWLEDGMENT: Quan Zhou thanks the University Students’ Innovative Undertaking
Training Program for financial support.
Supporting Information Available. Copy of 1H and 13C NMR spectra of compounds 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
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(16) Two other wellꢀknown and also easily available NHCꢀPd(II) complexes from Nolan and Organ’s
groups with high catalytic activity in crossꢀcoupling reactions were also checked for such reaction, and
similar good results were achieved, respectively (see Supporting Information for more details). For
selected papers, please see: (a) Viciu, M. S.; Germaneau, R. F.; Nolan, S. P. Org. Lett. 2002, 4, 4053ꢀ
4056. (b) Viciu, M. S.; Navarro, O.; Germaneau, R. F.; Kelly, R. A., III; Sommer, W.; Marion, N.;
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Chem. Eur. J. 2006, 12, 4743ꢀ4748. (d) Organ, M. G.; Calimsiz, S.; Sayah, M.; Hoi, K. H.; Lough, A. J.
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(17) The additives maybe act as Lewis or Brønsted acids to activate benzo[b]furans in such
transformation. For some selected examples, please see: (a) Tang, D.ꢀT. D.; Collins, K. D.; Glorius, F. J.
Am. Chem. Soc. 2013, 135, 7450ꢀ7453. (b) Campeau, L.ꢀC.; Stuart, D. R.; Leclerc, J.ꢀP.; Bertrandꢀ
Laperle, M.; Villemure, E.; Sun, H.ꢀY.; Lasserre, S.; Guimond, N.; Lecavallier, M.; Fagnou, K. J. Am.
Chem. Soc. 2009, 131, 3291ꢀ3306. (c) Leclerc, J.ꢀP.; Fagnou, K. Angew. Chem. Int. Ed. 2006, 45, 7781ꢀ
7786.
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