Direct ortho arylation of 9-(pyridin-2-yl)-9 h-carbazoles bearing a removable directing group via palladium(II)-catalyzed C-H bond activation

Article abstract of DOI:10.1021/om301071m

A one-pot synthesis of ortho-arylated 9-(pyridin-2-yl)-9H-carbazoles via C-H bond activation is presented. Silver nitrate and tert-butyl alcohol were found to be the best oxidant and solvent for the process, respectively. The product yields are from modest to excellent, and the reaction showed sufficient functional group tolerance. p-Benzoquinone served as an important ligand for the transmetalation and reductive elimination steps in the catalytic process. The key intermediate of the reaction, a 9-(pyridin-2-yl)-9H-carbazole palladacycle, was isolated, and its structure was unequivocally confirmed by X-ray crystallography. No kinetic isotope effect (k_H/k_D = 1.00 ± 0.17) for the C-H bond activation step was observed. In addition, a Hammett experiment gave a negative ρ value,-2.16 ± 0.02. The directing group, pyridinyl, was demonstrated to be a removable functional group. Finally, a rational catalytic mechanism is presented on the basis of all experimental evidence.

Full text of DOI:10.1021/om301071m

Article
pubs.acs.org/Organometallics
Direct Ortho Arylation of 9‑(Pyridin-2-yl)‑9H‑carbazoles Bearing a
Removable Directing Group via Palladium(II)-Catalyzed C−H Bond
Activation
Jean-Ho Chu,* Chung-Chiu Wu, Deng-Hsiang Chang, Ya-Ming Lee, and Ming-Jung Wu*
Department of Chemistry, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
S
* Supporting Information
ABSTRACT: A one-pot synthesis of ortho-arylated 9-
(pyridin-2-yl)-9H-carbazoles via C−H bond activation is
presented. Silver nitrate and tert-butyl alcohol were found to
be the best oxidant and solvent for the process, respectively.
The product yields are from modest to excellent, and the
reaction showed sufficient functional group tolerance. p-
Benzoquinone served as an important ligand for the
transmetalation and reductive elimination steps in the catalytic
process. The key intermediate of the reaction, a 9-(pyridin-2-
yl)-9H-carbazole palladacycle, was isolated, and its structure
was unequivocally confirmed by X-ray crystallography. No
kinetic isotope effect (kH/kD = 1.00 0.17) for the C−H bond activation step was observed. In addition, a Hammett experiment
gave a negative ρ value, −2.16 0.02. The directing group, pyridinyl, was demonstrated to be a removable functional group.
Finally, a rational catalytic mechanism is presented on the basis of all experimental evidence.
pyridinyl group via C−H bond activation are presented. We
not only illustrate the role of the directing group in the reaction
but also demonstrate its ease of removal.
INTRODUCTION
■
In the past decade, transition-metal-catalyzed direct carbon−
hydrogen (C−H) bond activation/functionalization has
emerged as a powerful protocol for the construction of new
carbon−carbon (C−C) bonds and carbon−heteroatom (C−X,
X = N, O, S, B, Si) bonds in organic synthesis.1 To date, many
practical syntheses based on these ideas have been widely
reported in literature.2
In 2006, a pioneering work on a Suzuki−Miyaura type C−H
bond activation/C−C bond cross-coupling reaction was
reported by Yu and co-workers.3 In that context, they
successfully demonstrated palladium(II)-catalyzed alkylation
of sp2 and sp3 C−H bonds with methylboroxine and
alkylboronic acids. After that, the Shi4 and Wu2j groups
reported a selective direct arylation of acetyl amides and 3,5-
diphenylisoxazole with a variety of arylboronic acids via C−H
bond activation in time sequence.
The carbazole structure is a crucial motif in natural
products,5 pharmaceuticals,6 and optoelectronic materials.7 In
general, direct functionalization on simple carbazoles is not easy
due to their intrinsic inertness. Therefore, the development of
efficient methods to modify simple carbazoles is still an
important issue, in which direct and specific ortho arylation is
especially challenging. To the best of our knowledge, only a few
examples of the ortho phenylation of carbazoles have been
reported.8
Herein we report the first example of palladium(II)-catalyzed
regioselective direct ortho arylation of carbazoles bearing a
directing group (pyridinyl). Various syntheses of ortho-arylated
9-(pyridin-2-yl)-9H-carbazoles from carbazoles bearing a
RESULTS AND DISCUSSION
■
Screens of Oxidants and Solvents for Ortho Arylation
of 9-(Pyridin-2-yl)-9H-carbazole (1) via C−H Bond
Activation. The synthesis of ortho-arylated 9-(pyridin-2-yl)-
9H-carbazoles 3 was initially investigated by the reaction of 9-
(pyridin-2-yl)-9H-carbazole (1) with potassium phenyltrifluor-
oborate (2a) via C−H bond activation. We herein utilized
palladium(II) acetate as the catalyst and screened a variety of
oxidants and solvents for the reaction in the presence of p-
benzoquinone (BQ) at 60−70 °C9a for 24 h. The screening
results are summarized in Table 1. Silver nitrate and tert-butyl
alcohol were found to be the best oxidant and solvent,
respectively, for the synthesis of compound 3a (entry 2, Table
1).
Catalytic Reaction of 9-(Pyridin-2-yl)-9H-carbazole (1)
and Substrates 5 with Borane Reagents 2. With the
optimized reaction conditions in hand (2 equiv of Ar-BF3K, 10
mol % of Pd(OAc)2, 3 equiv of AgNO3, 1 equiv of BQ in tert-
butyl alcohol at 60−70 °C for 24 h), we subsequently carried
out the direct ortho arylation of 1 with a variety of potassium
aryltrifluoroborates 2. The results are summarized in Table 2.
These reactions produced the predominant product 3 in
Received: November 8, 2012
Published: December 18, 2012
© 2012 American Chemical Society
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Article
preferentially took place at the more electron rich ring. In
addition, a 29:22:49 product ratio of 6d−8d (90% total yield)
was observed in the reaction of 5d with 2a. We found that the
reactivity of 5d was enhanced by the electron-donating group
(i.e., OMe) in the reaction and resulted in diphenylated
compound 8d (49% product ratio) as the major product;
moreover, no obvious regioselectivity for the formation of 6d
(29% product ratio) and 7d (22% product ratio) was observed.
On the basis of the experimental results of the above two
cases, we conclude that a strong electron-donating group (e.g.,
OMe) can induce and promote the phenylation to occur on the
more electron rich ring, although steric effects are still
dominant here. For the reaction of 5g with 2a, the single
product 6g was obtained in 53% yield (entry 7, Table 3).
Finally, we found that no desired phenylated products 6h,i were
generated in these reactions of 5h,i with 2a (entries 8 and 9,
Table 3). Most of the starting materials 5h,i was recovered after
the reaction, and some of 5i possibly formed metal complexes
with palladium or silver cation that hampered the catalytic
reaction.
Investigation of Kinetic Isotope Effects and Hammett
Experiments. In order to gain an insight into the catalytic
mechanism of the reaction, we carried out a kinetic isotope
effect (KIE) experiment by the reaction of monodeuterated 9-
(pyridin-2-yl)-9H-carbazole (1-D)11b with potassium 4-formyl-
phenyltrifluoroborate (2d)12 under the optimized reaction
conditions. The value of kH/kD was determined to be 1.00
0.17 in comparison with the standard spectra of 1 and 3d
(Scheme 1). This KIE result13 implies that C−H bond cleavage
is not the rate-determining step.
On the other hand, we also carried out a Hammett
experiment14 by using the reaction of palladacycle I with a
variety of para-substituted phenylborane reagents 2 for the
catalytic reaction, and it showed a negative ρ value, ρ = −2.16
0.02, with a reasonable correlation (R2 = 0.90, Figure 2). The
Hammett results imply that the reaction builds up positive
charge at the reaction center in the transition state.
Characterization of the 9-(Pyridin-2-yl)-9H-carbazole
Palladacycle I and Control Experiments in the Presence
or Absence of BQ. In addition to dynamic studies (KIE and
Hammett experiments), we also independently synthesized the
key intermediate, 9-(pyridin-2-yl)-9H-carbazole palladacycle I,
by the reaction of 1 with a stoichiometric equivalent of
palladium(II) acetate in dichloromethane (Scheme 2). The X-
ray crystallography results show that I adopts a head-to-tail
geometry, as shown in Figure 3.15 This strongly implies that the
direct cross-coupling reaction of 1 with 2 should proceed via
intermediate I.
Table 1. Screens of Oxidants and Solvents for Direct Ortho
Arylation of 9-(Pyridin-2-yl)-9H-carbazole (1)
a
entry
oxidant
absent
solvent
total yield, % (3a:4a)
1
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
tert-butyl alcohol
dichloromethane
9 (100:0)
95 (75:25)
57 (98:2)
41 (99:1)
34 (95:5)
12 (100:0)
5 (100:0)
10 (100:0)
3 (100:0)
10 (100:0)
59 (98:2)
55 (99:1)
58 (100:0)
51 (100:0)
49 (92:2)
30 (100:0)
25 (100:0)
10 (100:0)
2
AgNO3
Ag2O
3
4
AgOAc
Ag2CO3
Cu(OTf)2
5
9b
9b
6
7
Cu(OAc)2
oxone
8
9
K2S2O8
O2
10
11
12
13
14
15
16
17
18
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
b
DCE
benzene
toluene
1,4-dioxane
DMF
THF
acetonitrile
a
The total yield was obtained as an average by GC-MS spectroscopy
for three runs (using n-octadecane as the internal standard). The
product ratio 3a:4a was determined by GC-MS spectroscopy for three
b
runs. DCE = 1,2-dichloroethane.
modest to good yields (47−95%, entries 1−13, Table 2) with a
few concomitant diarylated products 4. In addition, no desired
products 3n−p were observed when borane reagents 2n−p
were used (entries 14−16, Table 2). Finally, the structures of
3a and 4a were unequivocally characterized by X-ray
crystallography (Figure 1).10
In addition to 9-(pyridin-2-yl)-9H-carbazole (1), we also
prepared a variety of 9-(pyridin-2-yl)-9H-carbazoles 5a−k11a
with different substituents on the carbazole ring and further
investigated the electronic or steric effects on the regioselec-
tivity of the ortho phenylation with potassium phenyl-
trifluoroborate (2a) under the aforementioned optimal reaction
conditions. The experimental results are summarized in Table
3. We herein found that most of 5 can successfully be
transformed into the anticipated products 6, 7, and even 8 in
modest to excellent yields (45−98%, entries 1−7, Table 3),
except for 5h,i (entries 8 and 9, Table 3).
On the basis of experimental results, the direct ortho
phenylation was found to preferentially occur at the less
sterically hindered side when the substituent is tagged at the
meta position, such as in 5a,e,f (entries 1, 5, and 6, Table 3).
Nevertheless, a mixture of 6c−8c (product ratio 55:36:9) was
obtained by the reaction of 5c with 2a in 57% total yield (entry
3, Table 3). In this case, either steric hindrance or electronic
effects appear to be in effect, but the former is slightly
predominant over the latter. On the other hand, the formation
of products 6b,d and 7b,d were observed by the reaction of
5b,d with 2a, respectively, in which the substituent (NO2 and
OMe) is tagged at the para position (entries 2 and 4, Table 3).
In the case of 5b, a 77:23 product ratio of 6b and 7b was
observed in 45% total yield, where the direct phenylation
On the other hand, we further investigated the essentiality of
BQ in the catalytic reaction. Subsequently, the reaction of
intermediate I with 2a in the presence or absence of BQ was
carried out (Scheme 3). The experimental results showed that
the desired product 3a was only obtained by the addition of
BQ, whereas 3a was not detected (by GC-MS spectroscopy)
when BQ did not exist in the reaction. This indicated that BQ
still serves as a critical promoter in the transmetalation and
reductive-elimination process of the catalytic reaction.2g,3,16
Proposed Catalytic Mechanism. According to the above
results of mechanistic investigations, a rational catalytic
mechanism is proposed for the direct ortho arylation of 1
with arylborane 2, as shown in Figure 4. Initially, Pd(II) is
coordinated with the nitrogen atom of pyridine ring of 9-
(pyridin-2-yl)-9H-carbazole (1) and, subsequently, the ortho
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Table 2. Direct Ortho Arylation of 9-(Pyridin-2-yl)-9H-carbazole (1)
a
b
The product ratio 3a:4a was determined by GC-MS spectroscopy for three runs. The product yield was obtained as an average by GC-MS
c
spectroscopy for three runs (using n-octadecane as the internal standard). Three equivalents of borane reagent 2c was used.
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Figure 1. ORTEP drawings of (a) 1-phenyl-9-(pyridin-2-yl)-9H-carbazole (3a) and (b) 1,8-diphenyl-9-(pyridin-2-yl)-9H-carbazole (4a).10 All
hydrogen atoms are omitted for clarity. Ellipsoids are shown at the 30% probability level.
C−H bond of the carbazole ring is cleaved by Pd(II) to form I.
Then, BQ coordinates with the Pd(II) center of I through a
ligand-exchange process to form intermediate II-A.17 After that,
aryldifluoroborane 2-BF2 (generated from 2)2g,h,18 and II-A
participate in the transmetalation step to generate intermediate
III by the release of F2BOAc. Finally, intermediate III is
converted into the desired product 3, with the release of Pd(0)
and BQ, through a reductive-elimination step. Pd(II) is
regenerated by the reoxidation of Pd(0) by Ag(I) and/or BQ
with the release of Ag(0) and/or hydroquinone, and the
regenerated Pd(II) re-enters the catalytic cycle.
Removal of the Directing Group of 1-Aryl-9-(pyridin-
2-yl)-9H-carbazoles 3. In many natural products and
pharmaceutical compounds, 9H-carbazole is a common
structural motif. If we can further remove the directing group
(i.e., pyridinyl) of arylated products, it would complete our
synthetic approach to modified carbazoles. To demonstrate the
pyridinyl group can be not only a directing group but also a
removable group, adducts 3a,b,k bearing neutral (H), electron-
withdrawing (NO2), and electron-donating (OMe) groups,
respectively, were chosen as model substrates for the removal of
the directing group. Compounds 3a,b,k then underwent
depyridination by treatment of methyl trifluoromethanesulfo-
nate (MeOTf) in dichloromethane and sodium hydroxide in
methanol.19 Eventually, 1-aryl-9H-carbazoles 9a,b,k were
produced in 80%, 75%, and 70% yields, respectively (Scheme
4).
Synthesis of Hyellazole (15). To further demonstrate the
possible application of our newly developed synthetic strategy,
we chose to tackle the synthesis of hyellazole (15), the first
carbazole alkaloid of marine origin that was isolated from a
blue-green algae, Hyella caespitosa, and reported by Moore et al.
in 1979.20 In order to synthesize it, we first prepared the
starting material 10 (see the Supporting Information) and
subsequently carried out the direct phenylation of 10 with 2a
under the optimized reaction conditions.
The experimental results showed that compound 11 was
formed as a major product and 12 as a minor adduct with a
trace of diphenylated product 13 (product ratio 11:12:13 =
85:10:5) in 81% total product yield due to the steric hindrance
of the methyl group (Scheme 5). Unfortunately, the minor
product 12 is the desired precursor of the target compound,
hyellazole (15). Even so, the successful removal of pyridnyl
groups on 11 and 12 was achieved and the new hyellazole
analogue 14 and hyellazole (15) were obtained in 87% and 81%
yields, respectively (Scheme 5).
CONCLUSION
■
We have successfully developed a simple and mild one-pot
synthesis of 3 through direct ortho arylation of 1 with 2 via C−
H bond activation using palladium(II) acetate as the catalyst.
The key intermediate I was isolated, and its structure was
unequivocally determined by X-ray crystallography. KIE for the
C−H bond activation step and a Hammett experiment for the
reaction transition state were all investigated. These results
provided strong evidence to support the proposed catalytic
mechanism. The directing group, pyridinyl, was successfully
demonstrated to be a removable functional group. Finally, the
reported synthetic methodology provides a fast and convenient
path to synthesize ortho-arylated carbazoles, which, in turn, has
potential applications in the fields of pharmaceutical chemistry
and optoelectronics.
EXPERIMENTAL SECTION
■
General Considerations. Solvents were purchased from Echo and
Mallinckrodt (ACS grade: n-hexane, ethyl acetate, and dichloro-
methane). Reagents were purchased from Aldrich, Acros, Alfa, TCI,
and Seedchem. All solvents and reagents were used without
1
purification. H NMR spectra were measured on 300 MHz Bruker
AVIII-300 and 500 MHz Varian Unity plus 500 spectrometers.
Natural-abundance 13C NMR spectra were measured using pulse
Fourier transform Bruker AVIII-300 (300 MHz NMR) and Varian
Unity plus 500 (500 MHz NMR) spectrometers operating at 75 and
125 MHz, respectively. Chemical shifts are given in parts per million
(ppm) and coupling constant J in hertz (Hz) for both nuclei, with the
solvent (usually CDCl3) peak as an internal standard. The reference
1
peak for H is δ 0.00 of TMS, and for 13C it is the central peak at δ
77.0. Low- and high-resolution mass spectrometry was performed on
Finnigan/Thermo Quest MAT 95XL and Shimadzu QP2010
spectrometers. Melting points were determined using a Barnstead
International-Electrothermal IA1101D melting point meter.
General Procedure for Direct Ortho Arylation of 9-(Pyridin-
2-yl)-9H-carbazoles 1 and 5 with Potassium Aryltrifluorobo-
rates 2. (a) A well-stirred solution of 9-(pyridin-2-yl)-9H-carbazole
(1; 20.0 mg, 0.082 mmol) with potassium aryltrifluoroborates 2 (2
equiv), 10 mol % Pd(OAc)2, AgNO3 (3 equiv), and BQ (1 equiv) in
tert-butyl alcohol (4 mL) was heated to 60−70 °C and stirred at this
temperature for 24 h. After it was cooled to room temperature, the
solution was filtered through a pad of Celite and washed with water (5
mL × 2). The aqueous layers were combined and extracted with
dichloromethane (5 mL × 2). Finally, the organic layers were
combined, dried over MgSO4, filtered, and evaporated under vacuum.
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compounds 3 and 4. All product yields determined by GC-MS
spectroscopy using n-octadecane as the internal standard are shown as
follows: 3a, 71% (19 mg, 0.058 mmol); 3b, 73% (22 mg, 0.060 mmol);
3c, 48% (15 mg, 0.040 mmol); 3d, 77% (22 mg, 0.063 mmol); 3e,
78% (22 mg, 0.064 mmol); 3f, 79% (23 mg, 0.065 mmol); 3g, 69%
(23 mg, 0.056 mmol); 3h, 47% (17 mg, 0.038 mmol); 3i, 74% (23 mg,
0.061 mmol); 3j, 65% (18 mg, 0.053 mmol), 3k, 64% (18 mg, 0.052
mmol), 3l, 75% (21 mg, 0.061 mmol), 3m, 88% (27 mg, 0.072 mmol);
4a, 24% (7.7 mg, 0.019 mmol); 4j, 20% (7.1 mg, 0.017 mmol); 4k, 9%
(4 mg, 0.008 mmol); 4l, 8% (3 mg, 0.007 mmol).
Table 3. Direct Ortho Phenylation of 9-(Pyridin-2-yl)-9H-
carbazoles 5
(b) The general procedure for the synthesis of compounds 6−8 was
the same with that for compounds 3 and 4. The amounts used of 5 are
shown as follows, 5a, 24 mg, 0.083 mmol; 5b, 24 mg, 0.083 mmol; 5c,
24 mg, 0.084 mmol; 5d, 25 mg, 0.083 mmol; 5e, 23 mg, 0.084 mmol;
5f, 23 mg, 0.084 mmol; 5g, 30 mg, 0.075 mmol. All product yields
determined by GC-MS spectroscopy using n-octadecane as the
internal standard are shown as follows: 6a, 64% (20 mg, 0.053
mmol); 6b, 35% (11 mg, 0.029 mmol); 6c, 31% (9 mg, 0.026 mmol);
6d, 26% (8 mg, 0.022 mmol); 6e, 98% (31 mg, 0.082 mmol); 6f, 58%
(18 mg, 0.049 mmol); 6g, 53% (19 mg, 0.040 mmol); 7b, 10% (3 mg,
0.009 mmol); 7c, 21% (6.0 mg, 0.017 mmol); 7d, 20% (5.8 mg, 0.017
mmol); 8c, 44% (16 mg, 0.037 mmol).
1-Phenyl-9-(pyridin-2-yl)-9H-carbazole (3a): white solid; mp 147−
1
148 °C; Rf = 0.61 (n-hexane/ethyl acetate = 5/1); H NMR (300
MHz, CDCl3) δ 6.74 (d, 1 H), 6.95 (dd, J = 7.4, 4.8 Hz, 1 H), 7.02−
7.05 (m, 3 H), 7.13−7.17 (m, 2 H), 7.22 (dd, J = 7.7, 2.0 Hz, 1 H),
7.32 (dd, J = 7.5, 7.5 Hz, 1 H), 7.38−7.44 (m, 3 H), 7.64 (d, J = 8.1
Hz, 1 H), 8.15−8.18 (m, 2 H), 8.37 (dd, J = 5.3, 1.7 Hz, 1 H); 13C
NMR (75 MHz, CDCl3) δ 111.0 (CH), 119.4 (CH), 120.0 (CH),
120.9 (CH), 121.1 (CH), 121.2 (CH), 121.7 (CH), 124.0 (Cq), 125.8
(Cq), 126.2 (CH), 126.4 (CH), 126.9 (Cq), 127.7 (CH × 2), 128.6
(CH × 3), 136.7 (CH), 137.2 (Cq), 139.7 (Cq), 141.6 (Cq), 148.4
(CH), 151.5 (Cq); MS (EI, m/z) 320 (M+, 100); HRMS m/z calcd
for C23H16N2 320.1313, found 320.1318.
1-(4-Nitrophenyl)-9-(pyridin-2-yl)-9H-carbazole (3b): yellow-
green solid; mp 212−213 °C; Rf = 0.58 (n-hexane/ethyl acetate =
1
4/1); H NMR (300 MHz, CDCl3) δ 6.92 (d, J = 8.1 Hz, 1 H), 6.99
(ddd, J = 7.4, 4.8, 0.9 Hz, 1 H), 7.31−7.46 (m, 7 H), 7.58 (d, J = 8.1
Hz, 1 H), 7.90 (d, J = 8.7 Hz, 2 H), 8.17 (d, J = 7.8 Hz, 1 H), 8.22 (dd,
J = 7.2, 1.7 Hz, 1 H), 8.31 (dd, J = 4.5, 1.5 Hz, 1 H); 13C NMR (75
MHz, CDCl3) δ 110.8 (CH), 120.3 (CH), 120.8 (CH), 121.1 (CH),
121.4 (CH), 121.6 (CH), 121.8 (CH), 122.8 (CH × 2), 123.8 (Cq),
124.3 (Cq), 126.2 (Cq), 126.9 (CH), 128.3 (CH), 129.2 (CH × 2),
137.1 (Cq), 137.4 (CH), 141.5 (Cq), 146.0 (Cq), 146.9 (Cq), 149.0
(CH), 151.5 (Cq); MS (EI, m/z) 365 (M+, 15), 70 (61), 61 (100);
HRMS m/z calcd for C23H15N3O2 365.1164, found 365.1166.
1-(3-Nitrophenyl)-9-(pyridin-2-yl)-9H-carbazole (3c): yellow vis-
1
cous liquid; Rf = 0.45 (n-hexane/ethyl acetate = 4/1); H NMR (300
MHz, CDCl3) δ 6.96 (ddd, J = 7.2, 5.3, 0.9 Hz, 1 H), 7.01 (d, J = 8.1
Hz, 1 H), 7.23 (dd, J = 7.8, 7.8 Hz, 1 H), 7.31−7.45 (m, 5 H), 7.50−
7.55 (m, 2 H), 7.88−7.94 (m, 2 H), 8.16 (d, J = 7.8 Hz, 1 H), 8.20−
8.23 (m, 2 H); 13C NMR (75 MHz, CDCl3) δ 110.6 (CH), 120.3
(CH), 120.6 (CH), 121.0 (CH × 2), 121.3 (CH), 121.8 (CH), 123.4
(CH), 123.7 (Cq), 124.1 (Cq), 126.0 (Cq), 126.8 (CH), 128.4 (CH),
128.6 (CH), 134.5 (CH), 137.1 (Cq), 137.4 (CH), 141.5 (Cq × 2),
147.5 (Cq), 149.1 (CH), 151.2 (Cq); MS (EI, m/z) 365 (M+, 76), 129
(45), 88 (52), 70 (64), 61 (100); HRMS m/z calcd for C23H15N3O2
365.1164, found 365.1158.
1-(4-Formylphenyl)-9-(pyridin-2-yl)-9H-carbazole (3d): white
solid; mp 177−178 °C; Rf = 0.37 (n-hexane/ethyl acetate = 4/1);
1H NMR (300 MHz, CDCl3) δ 6.85 (d, J = 8.1 Hz, 1 H), 6.93 (dd, J =
7.2, 5.1 Hz, 1 H), 7.28 (dd, J = 7.5, 1.8 Hz, 1 H), 7.32−7.37 (m, 3 H),
7.40−7.46 (m, 3 H), 7.56 (d, J = 8.1 Hz, 2 H), 7.61 (d, J = 8.1 Hz, 1
H), 8.17 (d, J = 7.8 Hz, 1 H), 8.21 (dd, J = 6.0, 3.0 Hz, 1 H), 8.31 (dd,
J = 4.5, 1.2 Hz, 1 H), 9.90 (s, 1 H); 13C NMR (75 MHz, CDCl3) δ
110.8 (CH), 120.2 (CH), 120.4 (CH), 121.0 (CH), 121.2 (CH),
121.5 (CH × 2), 123.8 (Cq), 125.3 (Cq), 126.0 (Cq), 126.7 (CH),
128.4 (CH), 129.0 (CH), 129.1 (Cq + CH), 134.2 (Cq), 137.1 (CH),
141.5 (Cq), 146.4 (Cq), 148.8 (CH), 151.4 (Cq), 191.8 (CH); MS
a
The product ratio 6:7:8 was determined by GC-MS spectroscopy for
b
three runs. The product yield was obtained as an average by GC-MS
spectroscopy for three runs (using n-octadecane as the internal
standard).
The residue was purified by silica gel chromatography using n-hexane/
ethyl acetate (50/1 to 10/1) as the eluent to give a series of
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Scheme 1. Kinetic Isotope Effect Experiment for Direct Ortho Arylation of 9-(Pyridin-2-yl)-9H-carbazole (1)
Figure 3. ORTEP drawing of the N-pyridylcarbazole palladacycle I.15
Selected bond lengths (Å): Pd1−Pd2 = 2.8861(4); Pd1−N2 =
2.052(3); Pd1−C1 = 1.955(3); Pd1−O1 = 2.045(2); Pd1−O4 =
2.172(2); Pd2−N4 = 2.022(3); Pd2−C18 = 1.964(3); Pd2−O2 =
2.143(2); Pd2−O3 = 2.042(2). All hydrogen atoms are omitted for
clarity. Ellipsoids are shown at the 30% probability level.
8.39 (dd, J = 5.4, 1.5 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ 110.9
(CH), 119.8 (CH), 120.1 (CH), 120.9 (CH), 121.1 (CH), 121.4
(CH), 121.8 (CH), 123.9 (Cq), 125.5 (Cq), 125.9 (Cq), 126.6 (CH),
127.8 (CH × 2), 128.4 (CH), 129.8 (CH × 2), 132.3 (CH), 137.0
(CH), 137.2 (Cq), 138.3 (Cq), 141.6 (Cq), 148.7 (CH), 151.5 (Cq);
MS (EI, m/z) 356 (M+ + 2, 5), 354 (M+, 16), 88 (48), 70 (63), 61
(100); HRMS m/z calcd for C23H15N235Cl 354.0924, found 354.0927.
1-(4-Bromophenyl)-9-(pyridin-2-yl)-9H-carbazole (3g): white
solid; mp 194−195 °C; Rf = 0.64 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 6.79 (d, J = 7.8 Hz, 1 H), 7.00−7.08
(m, 3 H), 7.16 (d, J = 8.4 Hz, 2 H), 7.30−7.44 (m, 5 H), 7.59 (d, J =
Figure 2. Hammett experiment for direct ortho arylation of 9-
(pyridin-2-yl)-9H-carbazole (1).
Scheme 2. Synthesis of the 9-(Pyridin-2-yl)-9H-carbazole
Palladacycle I
8.1 Hz, 1 H), 8.14−8.18 (m, 2 H), 8.38 (dd, J = 4.8, 1.4 Hz, 1 H); 13
C
NMR (75 MHz, CDCl3) δ 110.9 (CH), 119.8 (CH), 120.1 (CH),
120.3 (Cq), 120.9 (CH), 121.1 (CH), 121.4 (CH), 121.8 (CH), 123.8
(Cq), 125.5 (Cq), 125.9 (Cq), 126.6 (CH), 128.3 (CH), 130.2 (CH ×
2), 130.7 (CH × 2), 137.0 (CH), 137.1 (Cq), 138.7 (Cq), 141.6 (Cq),
148.7 (CH), 151.5 (Cq); MS (EI, m/z) 400 (M+ + 2, 34), 398 (M+,
35), 88 (31), 70 (53), 61 (100); HRMS m/z calcd for C23H15N279Br
398.0419, found 398.0426.
(EI, m/z) 348 (M+, 100), 88 (48), 70 (53), 61 (82); HRMS m/z calcd
for C24H16N2O 348.1263, found 348.1272.
1-(4-Fluorophenyl)-9-(pyridin-2-yl)-9H-carbazole (3e): white
solid; mp 208−209 °C; Rf = 0.61 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 6.70−6.78 (m, 3 H), 7.02 (ddd, J =
7.7, 4.8, 0.9 Hz, 1 H), 7.09−7.14 (m, 2 H), 7.29−7.44 (m, 5 H), 7.60
(d, J = 8.1 Hz, 1 H), 8.14−8.18 (m, 2 H), 8.38 (dd, J = 4.8, 1.4 Hz, 1
H); 13C NMR (75 MHz, CDCl3) δ 110.9 (CH), 114.6 (d, JC−F = 21.4
Hz, CH × 2), 119.6 (CH), 120.1 (CH), 120.9 (CH), 121.1 (CH),
121.4 (CH), 121.8 (CH), 123.9 (Cq), 125.8 (Cq), 125.9 (Cq), 126.5
1-(4-Iodophenyl)-9-(pyridin-2-yl)-9H-carbazole (3h): white solid;
1
mp 192−193 °C; Rf = 0.66 (n-hexane/ethyl acetate = 5/1); H NMR
(300 MHz, CDCl3) δ 6.79 (d, J = 8.1 Hz, 1 H), 6.89 (d, J = 8.4 Hz, 2
H), 7.07 (dd, J = 7.7, 4.8 Hz, 1 H), 7.30−7.44 (m, 7 H), 7.59 (d, J =
8.1 Hz, 1 H), 8.14−8.18 (m, 2 H), 8.39 (dd, J = 5.1, 1.2 Hz, 1 H); 13C
NMR (75 MHz, CDCl3) δ 91.6 (Cq), 110.8 (CH), 119.8 (CH), 120.1
(CH), 120.9 (CH), 121.1 (CH), 121.4 (CH), 121.8 (CH), 123.8
(Cq), 125.6 (Cq), 125.8 (Cq), 126.6 (CH), 128.2 (CH), 130.4 (CH ×
2), 130.7 (CH × 2), 137.0 (CH), 137.1 (Cq), 139.3 (Cq), 141.5 (Cq),
148.7 (CH), 151.4 (Cq); MS (EI, m/z) 446 (M+, 26), 88 (35), 70
(65), 61 (100); HRMS m/z calcd for C23H15N2I 446.0280, found
446.0286.
(CH), 128.5 (CH), 130.1 (d, JC−F = 8.0 Hz, CH × 2), 135.8 (d, JC−F
=
2.4 Hz, Cq), 136.9 (CH), 137.2 (Cq), 141.7 (Cq), 148.6 (CH), 151.5
(Cq), 161.5 (d, JC−F = 244.3 Hz, Cq); MS (EI, m/z) 338 (M+, 75), 88
(59), 70 (68), 61 (100); HRMS m/z calcd for C23H15N2F 338.1219,
found 338.1214.
1-(4-Chlorophenyl)-9-(pyridin-2-yl)-9H-carbazole (3f): white solid;
1
mp 200−201 °C; Rf = 0.64 (n-hexane/ethyl acetate = 4/1); H NMR
1-(4-tert-Butylphenyl)-9-(pyridin-2-yl)-9H-carbazole (3i): white
solid; mp 214−215 °C; Rf = 0.72 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 1.26 (s, 9 H), 6.67 (d, J = 7.8 Hz, 1
(300 MHz, CDCl3) δ 6.79 (d, J = 8.1 Hz, 1 H), 6.99−7.10 (m, 5 H),
7.30−7.44 (m, 5 H), 7.60 (d, J = 8.1 Hz, 1 H), 8.14−8.18 (m, 2 H),
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Scheme 3. Control Experiments in tert-Butyl Alcohol at 60−70 °C for 4 h: Reaction of I with 2a in the Presence or Absence of
BQ
Figure 4. Proposed catalytic mechanism for synthesis of 1-aryl-9-(pyridin-2-yl)-9H-carbazoles 3 by a palladium(II)-catalyzed cross-coupling reaction
of 1 with 2 via C−H bond activation.
1-(p-Tolyl)-9-(pyridin-2-yl)-9H-carbazole (3j): white solid; mp
147−148 °C; Rf = 0.62 (n-hexane/ethyl acetate = 5/1); H NMR
Scheme 4. Removal of Directing Group of 3a,b,k
1
(300 MHz, CDCl3) δ 2.24 (s, 3 H), 6.71 (d, J = 7.8 Hz, 1 H), 6.84 (d,
J = 8.0 Hz, 2 H), 6.96 (dd, J = 7.4, 4.8 Hz, 1 H), 7.03 (d, J = 8.0 Hz, 2
H), 7.22 (ddd, J = 7.8, 7.8, 2.1 Hz, 1 H), 7.32 (dd, J = 7.8, 7.8 Hz, 1
H), 7.38−7.43 (m, 3 H), 7.64 (d, J = 8.4 Hz, 1 H), 8.13−8.16 (m, 2
H), 8.38 (dd, J = 4.5, 1.5 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ
21.0 (CH3), 111.0 (CH), 119.2 (CH), 120.0 (CH), 120.9 (CH × 2),
121.8 (CH), 124.0 (Cq), 125.8 (Cq), 126.4 (CH), 126.9 (Cq), 128.4
(CH × 5), 128.5 (CH), 135.8 (Cq), 136.6 (CH), 136.8 (Cq), 137.3
(Cq), 141.6 (CH), 148.3 (Cq), 151.6 (Cq); MS (EI, m/z) 334 (M+,
37), 207 (54), 91 (38), 70 (55), 61 (100); HRMS m/z calcd for
C24H18N2 334.1470, found 334.1481.
1-(4-Methoxyphenyl)-9-(pyridin-2-yl)-9H-carbazole (3k): white
solid; mp 160−161 °C; Rf = 0.46 (n-hexane/ethyl acetate = 4/1);
1H NMR (300 MHz, CDCl3) δ 3.72 (s, 3 H), 6.58 (d, J = 8.7 Hz, 2
H), 6.71 (d, J = 8.1 Hz, 1 H), 6.98 (ddd, J = 7.3, 5.0, 0.8 Hz, 1 H), 7.06
(d, J = 8.7 Hz, 1 H), 7.23−7.43 (m, 5 H), 7.64 (d, J = 8.1 Hz, 1 H),
8.12−8.16 (m, 2 H), 8.40 (dd, J = 5.1, 1.5 Hz, 1 H); 13C NMR (75
MHz, CDCl3) δ 55.3 (CH3), 111.0 (CH), 113.3 (CH × 2), 119.0
(CH), 120.0 (CH), 120.9 (CH × 2), 121.1 (CH), 121.9 (CH), 124.0
(Cq), 125.8 (Cq), 126.4 (CH), 126.6 (Cq), 128.5 (CH), 129.6 (CH ×
H), 6.91 (ddd, J = 7.4, 5.0, 0.9 Hz, 1 H), 7.04 (m, 4 H), 7.17 (ddd, J =
7.8, 7.8, 1.8 Hz, 1 H), 7.29−7.43 (m, 4 H), 7.62 (d, J = 8.1 Hz, 1 H),
8.14−8.17 (m, 2 H), 8.36 (dd, J = 4.8, 1.7 Hz, 1 H); 13C NMR (75
MHz, CDCl3) δ 31.4 (CH3), 34.3 (Cq), 110.9 (CH), 119.2 (CH),
120.0 (CH), 120.8 (CH), 120.9 (CH), 121.0 (CH), 121.9 (CH),
123.9 (Cq), 124.6 (CH × 2), 125.6 (Cq), 126.4 (CH), 126.8 (Cq),
128.3 (CH × 2), 128.4 (CH), 136.5 (CH × 2), 137.3 (Cq), 141.6
(Cq), 148.2 (CH), 149.2 (Cq), 151.5 (Cq); MS (EI, m/z) 376 (M+,
100), 361 (60); HRMS m/z calcd for C27H24N2 376.1939, found
376.1944.
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Scheme 5. Synthesis of the Hyellazole Analogue 14 and Hyellazole (15)
2), 132.2 (Cq), 136.7 (CH), 137.2 (Cq), 141.7 (Cq), 148.3 (CH),
151.6 (Cq), 158.2 (Cq); MS (EI, m/z) 350 (M+, 21), 88 (61), 70
(69), 61 (100); HRMS m/z calcd for C24H18N2O 350.1419, found
350.1412.
(CH), 124.7 (Cq), 124.8 (CH), 125.7 (CH × 2), 127.1 (Cq), 127.2
(CH × 4), 129.0 (CH × 4), 129.4 (CH × 2), 135.5 (CH), 138.6 (Cq),
139.9 (Cq), 147.7 (CH), 151.7 (Cq); MS (EI, m/z) 396 (M+, 100);
HRMS m/z calcd for C29H20N2 396.1626, found 396.1622.
1-(3-Methoxyphenyl)-9-(pyridin-2-yl)-9H-carbazole (3l): pale yel-
low viscous liquid; Rf = 0.53 (n-hexane/ethyl acetate = 4/1); 1H NMR
(300 MHz, CDCl3) δ 3.63 (s, 3 H), 6.59 (dd, J = 8.1, 2.1 Hz, 1 H),
6.65 (s, 1 H), 6.75 (d, J = 8.1 Hz, 1 H), 6.80 (d, J = 7.5 Hz, 1 H),
6.94−7.01 (m, 2 H), 7.22−7.43 (m, 5 H), 7.63 (d, J = 8.1 Hz, 1 H),
8.14−8.17 (m, 2 H), 8.39 (dd, J = 4.8, 1.5 Hz, 1 H); 13C NMR (75
MHz, CDCl3) δ 55.0 (CH3), 111.0 (CH), 113.0 (CH), 113.5 (CH),
119.5 (CH), 120.1 (CH), 120.9 (CH), 121.0 (CH), 121.2 (CH),
121.3 (CH), 121.5 (CH), 123.9 (Cq), 125.8 (Cq), 126.5 (CH), 126.7
(Cq), 128.5 (CH), 128.8 (CH), 136.8 (CH), 137.0 (Cq), 141.1 (Cq),
141.6 (Cq), 148.3 (CH), 151.7 (Cq), 156.0 (Cq); MS (EI, m/z) 350
(M+, 100); HRMS m/z calcd for C24H18N2O 350.1419, found
350.1415.
9-(Pyridin-2-yl)-1,8-di-p-tolyl-9H-carbazole (4j): white solid; mp
213−214 °C; Rf = 0.55 (n-hexane/ethyl acetate = 1/5); 1H NMR (300
MHz, CDCl3) δ 2.19 (s, 6 H), 6.51 (d, J = 7.8 Hz, 1 H), 6.60 (dd, J =
7.2, 4.8 Hz, 1 H), 6.69 (d, J = 8.1 Hz, 4 H), 6.76 (d, J = 8.1 Hz, 4 H),
6.79 (ddd, J = 7.8, 7.8, 1.8 Hz, 1 H), 7.24 (dd, J = 6.6, 0.6 Hz, 2 H),
7.33 (dd, J = 7.2, 7.2 Hz, 2 H), 7.65 (dd, J = 5.1, 1.2 Hz, 1 H), 8.19
(dd, J = 7.5, 0.9 Hz, 2 H); 13C NMR (75 MHz, CDCl3) δ 21.0 (CH3 ×
2), 119.0 (CH × 2), 120.0 (CH × 2), 120.9 (CH), 124.7 (Cq × 2),
124.8 (CH), 127.1 (Cq × 2), 127.9 (CH × 4), 128.8 (CH × 4), 129.3
(CH × 2), 135.1 (CH), 135.3 (Cq × 2), 137.0 (Cq × 2), 138.6 (Cq ×
2), 147.5 (CH), 151.9 (Cq); MS (EI, m/z) 424 (M+, 100), 85 (45), 71
(59), 57 (77); HRMS m/z calcd for C31H24N2 424.1939, found
424.1938.
1-(Naphthalen-2-yl)-9-(pyridin-2-yl)-9H-carbazole (3m): white
solid; mp 146−147 °C; Rf = 0.58 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 6.61 (ddd, J = 7.2, 5.1, 0.6 Hz, 1 H),
6.74 (d, J = 8.1 Hz, 1 H), 6.96 (ddd, J = 7.8, 7.8, 1.8 Hz, 1 H), 7.28−
7.53 (m, 8 H), 7.60−7.72 (m, 4 H), 8.17−8.22 (m, 3 H); 13C NMR
(75 MHz, CDCl3) δ 111.0 (CH), 119.5 (CH), 120.1 (CH), 121.0
(CH × 3 + Cq), 121.6 (CH), 124.0 (Cq), 125.7 (CH), 125.9 (CH),
126.5 (CH), 126.7 (Cq), 126.8 (CH), 127.1 (CH), 127.4 (CH), 127.6
(CH), 127.8 (CH), 128.8 (CH), 131.8 (Cq), 133.0 (Cq), 136.6 (CH),
137.1 (Cq), 137.4 (Cq), 141.6 (Cq), 148.4 (CH), 151.5 (Cq); MS
(EI, m/z) 370 (M+, 100), 291 (20), 70 (32), 61 (66); HRMS m/z
calcd for C27H18N2 370.1470, found 370.1478.
1,8-Diphenyl-9-(pyridin-2-yl)-9H-carbazole (4a): white solid; mp
251−252 °C; Rf = 0.57 (n-hexane/ethyl acetate = 5/1); 1H NMR (300
MHz, CDCl3) δ 6.53−6.60 (m, 2 H), 6.80 (ddd, J = 7.8, 7.8, 1.8 Hz, 1
H), 6.88−6.96 (m, 10 H), 7.24−7.26 (m, 3 H), 7.35 (dd, J = 7.5, 7.5
Hz, 1 H), 7.66 (d, J = 4.5 Hz, 1 H), 8.21 (d, J = 7.5 Hz, 2 H); 13C
NMR (75 MHz, CDCl3) δ 119.2 (CH × 2), 120.1 (CH × 2), 121.6
1,8-Bis(4-methoxyphenyl)-9-(pyridin-2-yl)-9H-carbazole (4k):
white solid; mp 186−187 °C; Rf = 0.38 (n-hexane/ethyl acetate =
1
1/3); H NMR (300 MHz, CDCl3) δ 3.71 (s, 6 H), 6.45 (d, J = 8.7
Hz, 4 H), 6.55 (d, J = 7.8 Hz, 1 H), 6.66 (dd, J = 6.6, 5.1 Hz, 1 H),
6.80 (d, J = 8.7 Hz, 4 H), 6.89 (ddd, J = 7.5, 7.5, 1.8 Hz, 1 H), 7.23
(dd, J = 7.2, 0.9 Hz, 2 H), 7.33 (dd, J = 7.2, 7.2 Hz, 2 H), 7.74 (dd, J =
5.4, 1.5 Hz, 1 H), 8.19 (dd, J = 7.8, 0.9 Hz, 2 H); 13C NMR (75 MHz,
CDCl3) δ 55.3 (CH3 × 2), 112.8 (CH × 4), 119.0 (CH × 2), 120.0
(CH × 2), 121.3 (CH), 124.7 (CH), 124.9 (Cq × 2), 126.7 (Cq),
129.5 (CH × 2), 130.0 (CH × 4), 132.4 (Cq × 2), 135.4 (CH), 138.6
(Cq), 147.6 (CH), 152.0 (Cq), 157.7 (Cq × 2); MS (EI, m/z) 456
(M+, 72), 85 (62), 71 (89), 57 (100); HRMS m/z calcd for
C31H24O2N2 456.1838, found 456.1838.
1,8-Bis(3-methoxyphenyl)-9-(pyridin-2-yl)-9H-carbazole (4l):
white solid; mp 139−140 °C; Rf = 0.30 (n-hexane/ethyl acetate =
1
4/1); H NMR (300 MHz, CDCl3) δ 3.57 (s, 6 H), 6.36 (bs, 2 H),
6.51−6.66 (m, 6 H), 6.84−6.92 (m, 3 H), 7.26−7.37 (m, 5 H), 7.73
(d, J = 4.2 Hz, 1 H), 8.21 (dd, J = 7.8, 1.5 Hz, 1 H); 13C NMR (75
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MHz, CDCl3) δ 54.9 (CH3 × 2), 112.4 (CH × 2), 114.1 (CH × 2),
119.3 (CH × 2), 120.1 (CH × 2), 121.6 (CH), 121.7 (CH × 2), 124.4
(CH), 124.7 (Cq × 2), 126.8 (Cq × 2), 128.3 (CH × 2), 129.2 (CH ×
2), 135.3 (CH), 138.1 (Cq × 2), 141.2 (Cq × 2), 147.8 (CH), 151.9
(Cq), 158.4 (Cq × 2); MS (EI, m/z) 456 (M+, 48), 85 (64), 71 (84),
57 (100); HRMS m/z calcd for C31H24O2N2 456.1838, found
456.1838.
1-(8-Phenyl-9-(pyridin-2-yl)-9H-carbazol-2-yl)ethanone (6f): or-
ange solid; mp 136−137 °C; Rf = 0.28 (n-hexane/ethyl acetate = 4/1);
1H NMR (300 MHz, CDCl3) δ 2.65(s, 3 H), 6.78 (d, J = 7.8 Hz, 1 H),
6.98−7.05 (m, 4 H), 7.11−7.14 (m, 2 H), 7.28 (ddd, J = 7.8, 7.8, 1.8
Hz, 1 H), 7.41−7.49 (m, 2 H), 7.95 (dd, J = 8.1, 1.2 Hz, 1 H), 8.19−
8.22 (m, 3 H), 8.39 (dd, J = 4.8, 1.2 Hz, 1 H); 13C NMR (75 MHz,
CDCl3) δ 26.9 (CH3), 111.5 (CH), 119.9 (CH), 120.2 (CH), 121.3
(CH × 2), 121.7 (CH), 121.8 (CH), 124.8 (Cq), 126.4 (CH), 127.2
(Cq), 127.8 (CH × 2), 128.6 (CH × 2), 130.1 (CH), 135.4 (Cq),
137.0 (CH), 138.7 (Cq), 139.3 (Cq), 141.2 (Cq), 148.6 (CH), 150.9
(Cq), 198.2 (Cq); MS (EI, m/z) 362 (M+, 100), 347 (31), 319 (36),
85 (38), 71 (51), 57 (68); HRMS m/z calcd for C25H18ON2 362.1419,
found 362.1421.
3,6-Dibromo-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6g): color-
less viscous liquid; Rf = 0.50 (n-hexane/ethyl acetate = 5/1); 1H NMR
(300 MHz, CDCl3) δ 6.69 (d, J = 7.8 Hz, 1 H), 6.96−7.10 (m, 6 H),
7.25 (ddd, J = 8.1, 8.1, 2.1 Hz, 1 H), 7.48−7.54 (m, 3 H), 8.21 (s, 2
H), 8.35 (dd, J = 4.2, 1.2 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ
112.7 (CH), 113.9 (Cq), 114.1 (Cq), 121.5 (CH), 121.7 (CH), 122.1
(CH), 122.9 (CH), 124.5 (Cq), 126.2 (Cq), 126.8 (CH), 127.8 (CH
× 2), 128.4 (CH), 128.6 (Cq), 129.8 (CH), 131.5 (CH), 136.1 (Cq),
137.0 (CH), 137.9 (Cq), 140.5 (Cq), 148.5 (CH), 150.5 (Cq); MS
(EI, m/z) 476 (M+, 100); HRMS m/z calcd for C23H14N279Br2
475.9524, found 475.9522.
7-Nitro-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6a): yellow solid;
1
mp 160−161 °C; Rf = 0.44 (n-hexane/ethyl acetate = 5/1); H NMR
(300 MHz, CDCl3) δ 6.77 (d, J = 7.8 Hz, 1 H), 7.03−7.13 (m, 6 H),
7.29 (ddd, J = 7.5, 7.5, 1.8 Hz, 1 H), 7.46−7.54 (m, 2 H), 8.21−8.24
(m, 3 H), 8.43 (dd, J = 4.5, 1.5 Hz, 1 H), 8.49 (s, 1 H); 13C NMR (75
MHz, CDCl3) δ 107.5 (CH), 116.3 (CH), 120.2 (CH), 120.6 (CH),
121.7 (CH), 121.9 (CH), 122.1 (CH), 124.0 (Cq), 126.6 (CH), 127.5
(Cq), 127.9 (CH × 2), 128.6 (CH × 2), 128.9 (Cq), 130.9 (CH),
137.2 (CH), 138.8 (Cq), 139.3 (Cq), 140.6 (Cq), 146.4 (Cq), 148.9
(CH), 150.4 (Cq); MS (EI, m/z) 365 (M+, 100), 319 (20); HRMS m/
z calcd for C23H15O2N3 365.1164, found 365.1165.
6-Nitro-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6b): yellow solid;
1
mp 151−152 °C; Rf = 0.50 (n-hexane/ethyl acetate = 5/1); H NMR
(300 MHz, CDCl3) δ 6.75 (d, J = 8.1 Hz, 1 H), 7.04−7.11 (m, 6 H),
7.28 (ddd, J = 7.8, 7.8, 1.8 Hz, 1 H), 7.50 (s, 1 H), 7.51 (d, J = 2.4 Hz,
1 H), 7.60 (d, J = 9.0 Hz, 1 H), 8.24 (dd, J = 5.4, 3.6 Hz, 1 H), 8.31
(dd, J = 9.3, 2.4 Hz, 1 H), 8.42 (dd, J = 4.5, 1.5 Hz, 1 H), 9.09 (d, J =
2.1 Hz, 1 H); 13C NMR (75 MHz, CDCl3) δ 110.9 (CH), 116.9
(CH), 120.0 (CH), 121.9 (CH), 122.1 (CH), 122.2 (CH), 122.3
(CH), 123.7 (Cq), 124.9 (Cq), 126.6 (CH), 127.6 (Cq), 127.9 (CH ×
2), 128.6 (CH × 2), 130.3 (CH), 137.2 (CH), 138.3 (Cq), 138.7
(Cq), 142.2 (Cq), 144.6 (Cq), 148.7 (CH), 150.4 (Cq); MS (EI, m/z)
365 (M+, 100), 71 (50), 57 (84); HRMS m/z calcd for C23H15O2N3
365.1164, found 365.1166.
3-Nitro-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (7b): yellow solid;
mp 190−191 °C (obtained from the detection of a mixture, 6b and
1
7b); Rf = 0.50 (n-hexane/ethyl acetate = 5/1); H NMR (300 MHz,
CDCl3) δ 6.83 (d, J = 8.1 Hz, 1 H), 7.03−7.13 (m, 5 H), 7.35 (ddd, J
= 7.8, 7.8, 1.8 Hz, 1 H), 7.42 (ddd, J = 6.6, 6.6, 1.5 Hz, 1 H), 7.47−
7.54 (m, 3 H), 8.22−8.25 (m, 1 H), 8.29−8.33 (m, 1 H), 8.36 (dd, J =
4.8, 1.2 Hz, 1 H), 9.07 (d, J = 2.1 Hz, 1 H); 13C NMR (75 MHz,
CDCl3) δ 111.5 (CH), 115.7 (CH), 120.7 (CH), 121.9−122.4 (CH ×
3), 123.4 (Cq), 123.9 (CH), 125.6 (Cq), 126.9 (Cq), 127.1 (CH),
128.0 (CH), 128.6 (CH), 130.3 (CH), 137.2 (CH), 137.6 (Cq), 140.2
(Cq), 141.8 (Cq), 142.7 (Cq), 148.9 (CH), 150.2 (Cq); MS (EI, m/z)
365 (M+, 100), 318 (40), 158 (20); HRMS m/z calcd for C23H15N3O2
365.1164, found 365.1162.
2-Methoxy-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (7c): white
solid; mp 176−177 °C; Rf = 0.46 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 3.83 (s, 3 H), 6.70 (d, J = 8.1 Hz, 1
H), 6.93 (ddd, J = 7.3, 5.3, 0.6 Hz, 1 H), 6.99−7.12 (m, 6 H), 7.20−
7.42 (m, 4 H), 8.05 (dd, J = 6.3, 2.1 Hz, 1 H), 8.09 (d, J = 8.4 Hz, 1
H), 8.31 (dd, J = 4.5, 1.2 Hz, 1 H); 13C NMR (125 MHz, CDCl3) δ
56.7 (CH3), 105.7 (CH), 110.6 (CH), 114.8 (Cq), 119.2 (CH), 119.7
(Cq), 119.8 (CH), 120.8 (CH), 121.2 (CH), 122.0 (CH), 123.8 (Cq),
125.2 (CH), 126.2 (CH), 127.4 (CH × 2), 130.6 (CH × 2), 134.6
(Cq), 136.8 (CH), 139.0 (Cq), 142.1 (Cq), 148.3 (CH), 151.3 (Cq),
156.0 (Cq); MS (EI, m/z) 350 (M+, 100), 335 (99); HRMS m/z calcd
for C24H18ON2 350.1419, found 350.1417.
3-Methoxy-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (7d): white
solid; mp 107−108 °C; Rf = 0.43 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 3.99 (s, 3 H), 6.71 (d, J = 8.1 Hz, 1
H), 6.92 (dd, J = 7.0, 5.1 Hz, 1 H), 7.02−7.06 (m, 4 H), 7.16−7.32
(m, 4 H), 7.39 (ddd, J = 7.7, 7.7, 0.9 Hz, 1 H), 7.63−7.67 (m, 2 H),
8.10 (d, J = 7.8 Hz, 1 H), 8.34 (dd, J = 4.5, 1.0 Hz, 1 H); 13C NMR
(125 MHz, CDCl3) δ 56.1 (CH3), 102.6 (CH), 111.1 (CH), 116.8
(CH), 120.0 (CH), 120.7 (CH), 120.8 (CH), 121.3 (CH), 124.0
(Cq), 126.4 (CH), 125.5 (CH), 126.6 (Cq), 127.7 (CH × 2), 127.8
(Cq), 128.4 (CH × 2), 132.1 (Cq), 136.6 (CH), 139.3 (Cq), 142.2
(Cq), 148.2 (CH), 151.6 (Cq), 154.7 (Cq); MS (EI, m/z) 350 (M+,
41), 154 (61), 57 (100); HRMS m/z calcd for C24H18ON2 350.1419,
found 350.1419.
7-Methoxy-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6c): white
solid; mp 122−123 °C; Rf = 0.41 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 3.84 (s, 3 H), 6.69 (d, J = 7.8 Hz, 1
H), 6.92−6.96 (m, 2 H), 7.01−7.03 (m, 3 H), 7.13−7.23 (m, 4 H),
7.31−7.40 (m, 2 H), 8.01 (d, J = 8.7 Hz, 1 H), 8.05 (dd, J = 7.2, 1.5
Hz, 1 H), 8.39 (dd, J = 4.5, 1.2 Hz, 1 H); 13C NMR (125 MHz,
CDCl3) δ 55.6 (CH3), 95.3 (CH), 109.6 (CH), 117.7 (Cq), 120.8
(CH), 121.0 (CH), 121.1 (CH), 121.5 (CH), 126.0 (Cq), 126.1
(CH), 126.7 (Cq), 127.3 (CH), 127.7 (CH × 2), 128.5 (CH × 2),
136.7 (CH), 137.1 (Cq), 139.7 (Cq), 142.9 (Cq), 148.2 (CH), 151.5
(Cq), 159.5 (Cq); MS (EI, m/z) 350 (M+, 100), 335 (32); HRMS m/
z calcd for C24H18ON2 350.1419, found 350.1420.
8-Methoxy-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6d): white
solid; mp 236−237 °C; Rf = 0.46 (n-hexane/ethyl acetate = 5/1);
1H NMR (300 MHz, CDCl3) δ 3.95 (s, 3 H), 6.69 (d, J = 7.8 Hz, 1
H), 6.93 (ddd, J = 8.9, 4.8, 0.9 Hz, 1 H), 7.02−7.06 (m, 4 H), 7.15−
7.23 (m, 3 H), 7.39 (dd, J = 11.1, 7.5 Hz, 1 H), 7.40 (s, 1 H), 7.59 (d, J
= 9.0 Hz, 1 H), 7.62 (d, J = 2.4 Hz, 1 H), 8.11 (dd, J = 6.3, 2.7 Hz, 1
H), 8.36 (dd, J = 5.4, 1.5 Hz, 1 H); 13C NMR (125 MHz, CDCl3) δ
56.0 (CH3), 102.8 (CH), 112.0 (CH), 115.3 (CH), 119.3 (CH), 120.6
(CH), 120.9 (CH), 121.3 (CH), 124.5 (Cq), 125.8 (Cq), 126.2 (CH),
127.0 (Cq), 127.7 (CH × 2), 128.5 (CH × 2), 128.6 (CH), 136.5
(Cq), 136.6 (CH), 137.6 (Cq), 139.7 (Cq), 148.2 (CH), 151.6 (Cq),
155.0 (Cq); MS (EI, m/z) 350 (M+, 100), 335 (79); HRMS m/z calcd
for C24H18ON2 350.1419, found 350.1422.
7-tert-Butyl-1-phenyl-9-(pyridin-2-yl)-9H-carbazole (6e): white
1
solid; mp 98−99 °C; Rf = 0.65 (n-hexane/ethyl acetate = 5/1); H
NMR (300 MHz, CDCl3) δ 1.37 (s, 9 H), 6.69 (d, J = 8.1 Hz, 1 H),
6.95 (ddd, J = 6.7, 5.1, 0.6 Hz, 1 H), 7.01−7.04 (m, 3 H), 7.14−7.24
(m, 3 H), 7.37−7.42 (m, 3 H), 7.69 (d, J = 0.9 Hz, 1 H), 8.07 (d, J =
8.4 Hz, 1 H), 8.11 (dd, J = 5.7, 3.3 Hz, 1 H), 8.42 (dd, J = 4.8, 1.2 Hz,
1 H); 13C NMR (75 MHz, CDCl3) δ 31.7 (CH3), 35.2 (Cq), 107.4
(CH), 119.1 (CH × 2), 119.5 (CH), 120.8 (CH), 121.0 (CH), 121.6
(Cq + CH), 125.9 (Cq), 126.1 (CH), 126.8 (Cq), 127.7 (CH × 2),
128.1 (CH), 128.6 (CH × 2), 136.7 (CH), 137.4 (Cq), 139.8 (Cq),
141.8 (Cq), 148.2 (CH), 150.3 (Cq), 151.7 (Cq); MS (EI, m/z) 376
(M+, 96), 361 (100); HRMS m/z calcd for C27H24N2 376.1939, found
376.1939.
2-Methoxy-1,8-diphenyl-9-(pyridin-2-yl)-9H-carbazole (8d): white
1
solid; mp 187−188 °C; Rf = 0.43 (n-hexane/ethyl acetate = 5/1); H
NMR (300 MHz, CDCl3) δ 3.97 (s, 3 H), 6.5 (d, J = 8.1 Hz, 1 H),
6.58 (dd, J = 6.6, 5.1 Hz, 1 H), 6.79 (ddd, J = 7.5, 7.5, 1.8 Hz, 1 H),
6.88−6.97 (m, 11 H), 7.24 (dd, J = 6.9, 0.9 Hz, 1 H), 7.32 (dd, J = 7.2,
7.2 Hz, 1 H), 7.65 (d, J = 6.0 Hz, 1 H), 7.68 (d, J = 2.7 Hz, 1 H), 8.16
(dd, J = 7.8, 0.9 Hz, 1 H); 13C NMR (125 MHz, CDCl3) δ 56.0
(CH3), 102.3 (CH), 117.8 (CH), 119.2 (CH), 119.7 (CH), 121.4
280
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Article
(CH), 124.6 (CH), 124.7 (Cq), 125.4 (Cq), 125.7 (CH), 125.9 (CH),
127.1 (Cq), 127.2 (CH × 4), 128.0 (Cq), 128.8 (CH × 2), 128.9 (CH
× 2), 129.4 (CH), 133.6 (Cq), 135.4 (CH), 139.0 (Cq), 139.4 (Cq),
139.8 (Cq), 147.6 (CH), 151.7 (Cq), 153.9 (Cq); MS (EI, m/z) 426
(M+, 38), 154 (92), 57 (100); HRMS m/z calcd for C30H22ON2
426.1732, found 426.1733.
(3) (a) 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, 3510−3511.
(b) Chen, X.; Li, J.-J.; Hau, X.-S.; Goodhue, C. E.; Yu, J.-Q. J. Am.
Chem. Soc. 2006, 128, 78−79. (c) Chen, X.; Goodhue, C. E.; Yu, J.-Q.
J. Am. Chem. Soc. 2006, 128, 12634−12635.
(4) Shi, Z.; Li, B.; Wan, X.; Cheng, J.; Fang, Z.; Cao, B.; Qin, C.;
Wang, Y. Angew. Chem., Int. Ed. 2007, 46, 5554−5558.
(5) (a) Maneerat, W.; Ritthiwigrom, T.; Cheenpracha, S.; Promgool,
T.; Yossathera, K.; Deachathai, S.; Phakhodee, W.; Laphookhieo, S. J.
ASSOCIATED CONTENT
* Supporting Information
Text, tables, figures, and CIF files giving general procedures for
■
S
Nat. Prod. 2012, 75, 741−746. (b) Knolker, H.-J.; Reddy, K. R. The
̈
Alkaloids: Chem. Biol. 2008, 65, 1−430. (c) Bergman, J.; Pelcman, B.
Pure Appl. Chem. 1990, 62, 1967−1976.
the preparation of all starting substrates, characterization of
1
compounds, X-ray crystallographic data, and H and 13C NMR
(6) (a) Patpi, S. R.; Pulipati, L.; Yogeeswari, P.; Sriram, D.; Jain, N.;
Sridhar, B.; Murthy, R.; Devi, T. A.; Kalivendi, S. V.; Kantevari, S. J.
spectra of new compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
́ ́
Med. Chem. 2012, 55, 3911−3922. (b) Akue-Gedu, R.; Rossignol, E.;
Azzaro, S.; Knapp, S.; Filippakopoulos, P.; Bullock, A. N.; Bain, J.;
Cohen, P.; Prudhomme, M.; Anizon, F.; Moreau, P. J. Med. Chem.
2009, 52, 6369−6381. (c) Prudhomme, M. Eur. J. Med. Chem. 2003,
38, 123−140.
(7) (a) Lai, M.-H.; Tsai, J.-H.; Chueh, C.-C.; Wang, C.-F.; Chen, W.-
C. Macromol. Chem. Phys. 2010, 211, 2017−2025. (b) Cho, M. J.; Jin,
J.-I.; Choi, D. H.; Kim, Y. M.; Park, Y. W.; Ju, B.-K. Dyes Pigm. 2009,
83, 218−224. (c) Cho, M. J.; Kim, J. I.; Hong, C. S.; Kim, Y. M.; Park,
Y. W.; Ju, B.-K.; Choi, D. H. J. Polym. Sci.: Part A: Polym. Chem. 2008,
46, 7419−7428. (d) Zhu, R.; Lin, J.; Wen, G.-A.; Liu, S.-J.; Wan, J.-H.;
Feng, J.-C.; Fan, Q.-L.; Zhong, G.-Y.; Wei, W.; Huang, W. Chem. Lett.
2005, 34, 1668−1669.
AUTHOR INFORMATION
Corresponding Author
*E-mail: j_hchu@yahoo.com.tw (J.-H.C.); mijuwu@faculty.
nsysu.edu.tw (M.-J.W.). Fax: +886-7-5253909.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Science Council of the Republic of
China (NSC-100-2113-M-110-008, NSC-101-2113-M-110-
014-MY3, and NSC-100-2113-M-110-006-MY3) for financial
support.
(8) (a) Ohta, T.; Miyake, S.; Shudo, K. Tetrahedron Lett. 1985, 26,
5811−5814. (b) Haga, K.; Iwaya, K.; Kaneko, R. Bull. Chem. Soc. Jpn.
1986, 59, 803−808.
(9) (a) The variation of temperature was carried out for the reaction,
and 60−70 °C was shown as the best reaction temperature. Detailed
information is summarized in the Supporting Information. (b) A 10
mol % amount of either Cu(OAc)2 or Cu(OTf)2 under an atmosphere
of O2 as the oxidative system was also investigated, but no desired
compound 3a was observed by 1H NMR spectroscopy and most of the
starting substrate 1 was recovered.
(10) Copies of the deposited crystallographic data (CCDC 890263
(3a) and 890264 (4a)) can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(11) (a) For details of the syntheses of 5a−k, please see the
Supporting Information. (b) For details of the synthesis of 1-D,
please see the Supporting Information.
(12) The reason for the use of potassium 4-formylphenyltrifluor-
oborate (2d) instead of potassium phenyltrifluoroborate (2a) was
mainly due to purification of 3d and 3a. Herein compound 3d is easier
to separate than 3a from their crude products.
(13) For the interpretation of KIE in C−H bond functionalization,
please see: Simmons, E. M.; Hartwig, J. F. Angew. Chem., Int. Ed. 2012,
51, 3066−3072.
(14) (a) Hammett, L. P. J. Am. Chem. Soc. 1937, 59, 96−103.
(b) Hammett, L. P. Chem. Rev. 1935, 17, 125−136.
(15) A copy of the deposited crystallographic data (CCDC 890265
(I)) can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
(16) Chen, X.; Li, J.-J.; Hao, X.-S.; Goodhue, C. E.; Yu, J.-Q. J. Am.
Chem. Soc. 2006, 128, 78−79.
(17) For theoretical calculations on a similar intermediate, see:
Ishikawa, A.; Nakao, Y.; Sato, H.; Sakaki, S. Dalton Trans. 2010, 39,
3279−3289.
(18) (a) Molander, G. A.; Cavalcanti, L. N.; Canturk, B.; Pan, P.-S.;
Kennedy, L. E. J. Org. Chem. 2009, 74, 7364−7369. (b) Ting, R.;
Harwing, C. W.; Lo, J.; Li, Y.; Adam, M. J.; Ruth, T. J.; Perrin, D. M. J.
Org. Chem. 2008, 73, 4662−4670.
(19) (a) Nishino, M.; Hirano, K.; Satoh, T.; Miura, M. Angew. Chem.,
Int. Ed. 2012, 51, 6993−6997. (b) Ackermann, L.; Lygin, A. V. Org.
Lett. 2012, 14, 764−767. (c) Ackermann, L.; Lygin, A. V. Org. Lett.
REFERENCES
■
(1) (a) Engle, K. M.; Mei, T.-S.; Wasa, M.; Yu, J.-Q. Acc. Chem. Res.
2012, 45, 788−802. (b) Colby, D. A.; Tsai, A. S.; Bergman, R. G.;
Ellman, J. A. Acc. Chem. Res. 2012, 45, 814−825. (c) Hartwig, J. F. Acc.
Chem. Res. 2012, 45, 864−873. (d) Neufeldt, S. R.; Sanford, M. S. Acc.
Chem. Res. 2012, 45, 936−946. (e) Zhang, C.; Tang, C.; Jiao, N. Chem.
Soc. Rev. 2012, 41, 3464−3484. (f) Song, G.; Wang, F.; Li, X. Chem.
Soc. Rev. 2012, 41, 3651−3678. (g) Yeung, C. S.; Dong, V. M. Chem.
Rev. 2011, 111, 1215−1292. (h) Sun, C.-L.; Li, B.-J.; Shi, Z.-J. Chem.
Rev. 2011, 111, 1293−1314. (i) Ackerman, L. Chem. Rev. 2011, 111,
1315−1345. (j) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110,
1147−1169. (k) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev.
2010, 110, 624−655. (l) Bellina, F.; Rossi, R. Chem. Rev. 2010, 110,
1082−1146. (m) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew.
Chem., Int. Ed. 2009, 48, 9792−9826. (n) Giri, R.; Shi, B.-F.; Engle, K.
M.; Maugel, N.; Yu, J.-Q. Chem. Soc. Rev. 2009, 38, 3242−3272.
(o) McGlacken, G. P.; Bataman, L. M. Chem. Soc. Rev. 2009, 38,
2447−2464. (p) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew.
Chem., Int. Ed. 2009, 48, 5094−5115. (q) Daugulis, O.; Do, H.-Q.;
Shabashov, D. Acc. Chem. Res. 2009, 42, 1074−1086. (r) Collet, F.;
Dodd, R. H.; Dauban, P. Chem. Commun. 2009, 5061−5074.
(s) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107,
174−238.
(2) (a) Leow, D.; Li, G.; Mei, T.-S.; Yu, J.-Q. Nature 2012, 486, 518−
522. (b) Ackermann, L.; Diers, E.; Manvar, A. Org. Lett. 2012, 14,
1154−1157. (c) Yadav, M. R.; Rit, R. K.; Sahoo, A. K. Chem. Eur. J.
2012, 18, 5541−5545. (d) Li, B.-J.; Wang, H.-Y.; Zhu, Q.-L.; Shi, Z.-J.
Angew. Chem., Int. Ed. 2012, 51, 3948−3952. (e) Wencel-Delord, J.;
Nimphius, C.; Patureau, F. W.; Glorius, F. Angew. Chem., Int. Ed. 2012,
51, 2247−2251. (f) Iglesias, A.; Alvarez, R.; de Lera, A. R.; Muniz, K.
̃
Angew. Chem., Int. Ed. 2012, 51, 2225−2228. (g) Chu, J.-H.; Lin, P.-S.;
Lee, Y.-M.; Shen, W.-T.; Wu, M.-J. Chem. Eur. J. 2011, 17, 13613−
13620. (h) Chu, J.-H.; Lin, P.-S.; Wu, M.-J. Organometallics 2010, 29,
4058−4065. (i) Chu, J.-H.; Tsai, S.-L.; Wu, M.-J. Synthesis 2009,
3757−3764. (j) Chu, J.-H.; Chen, C.-C.; Wu, M.-J. Organometallics
2008, 27, 5173−5176. (k) Karthikeyan, J.; Cheng, C.-H. Angew. Chem.,
Int. Ed. 2011, 50, 9880−9883. (l) Gandeepan, P.; Cheng, C.-H. J. Am.
Chem. Soc. 2010, 134, 5738.
281
dx.doi.org/10.1021/om301071m | Organometallics 2013, 32, 272−282

Organometallics
Article
2011, 13, 3332−3335. (d) Jana, C. K.; Grimme, S.; Studer, A. Chem.
Eur. J. 2009, 15, 9078−9084.
(20) Cardellina, J. H., II; Kirkup, M. P.; Moore, R. E.; Mynderse, J. S.;
Seff, K.; Simmons, C. J. Tetrahedron Lett. 1979, 4915−4916.
282
dx.doi.org/10.1021/om301071m | Organometallics 2013, 32, 272−282