Pd-catalyzed synthesis of 9,9-bifluorenylidene derivatives via dual C-H activation of bis-biaryl alkynes

Article abstract of DOI:10.1021/ja503252k

We report a novel Pd-catalyzed alkyne-directed dual C-H activation of bis-biaryl alkynes, which produced important and useful products, 9,9-bifluorenylidene (9,9BF) derivatives, in high yields with a broad range of functional group compatibility. The combination of the PdCl₂ catalyst with the MnO₂ oxidant and PivOH additive is vital for realization of the present catalytic transformation. Mechanistic evidence suggests that this intramolecular arene/alkyne annulation may take place through unusual dual C-H activation followed by annulation with alkynes.

Full text of DOI:10.1021/ja503252k

Communication
pubs.acs.org/JACS
Pd-Catalyzed Synthesis of 9,9′-Bifluorenylidene Derivatives via Dual
C−H Activation of Bis-biaryl Alkynes
Jian Zhao,† Naoki Asao,† Yoshinori Yamamoto,†,‡ and Tienan Jin*,†
†WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
‡State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, China
S
* Supporting Information
catalyzed C−H activation for the construction of polycyclic fused
aromatics,11 we reasoned that the successful implementation of
ABSTRACT: We report a novel Pd-catalyzed alkyne-
directed dual C−H activation of bis-biaryl alkynes, which
produced important and useful products, 9,9′-bifluoreny-
lidene (9,9′BF) derivatives, in high yields with a broad
range of functional group compatibility. The combination
of the PdCl2 catalyst with the MnO2 oxidant and PivOH
additive is vital for realization of the present catalytic
transformation. Mechanistic evidence suggests that this
intramolecular arene/alkyne annulation may take place
through unusual dual C−H activation followed by
annulation with alkynes.
the cyclization of bis-biaryl alkynes (1) through a dual C−H
activation by seeking appropriate transition-metal-catalyst
systems may provide a novel synthetic methodology for the
construction of 9,9′BF derivatives. Herein, we report an
unprecedented PdCl2-catalyzed dual C−H activation of bis-
biaryl alkynes (1) for the construction of 9,9′BF derivatives (2)
by combining with PivOH and the MnO2 oxidant (Scheme 1).
Scheme 1. Pd-Catalyzed Arene/Alkyne Annulation via Dual
C−H Activation of Bis-biaryl Alkynes
ransition-metal-catalyzed annulations of alkynes with
Tarenes via direct C−H functionalization without prior
functionalization of aromatic C−H bonds have attracted
increasing interest as one of the most powerful synthetic
methodologies for the construction of π-conjugated polycycles.1
One of the classical arene/alkyne annulations is intramolecular
electrophilic hydroarylation of alkynes catalyzed by palladium
and platinum complexes, and Lewis acids, which mainly or
exclusively proceeds through 6-endo-dig cyclization of electron-
rich aromatic rings.2−4 In contrast, the research group of
Gevorgyan reported an impressive Pd-catalyzed exclusive 5-exo-
dig cyclization of o-alkynylbiaryls having electron-neutral and
electron-deficient arenes, affording the fluorene derivatives in
high cis-stereoselectivity via a C(sp2)−H bond activation.5 On
the other hand, although only a few examples have been
reported, the arene/alkyne annulation via dual C−H bond
activation without using arylhalides has become a more
challenging methodology for the synthesis of various polycyclic
aromatic compounds.6,7 For example, Jiao et al. reported a Pd-
catalyzed oxidative cycloaromatization of biaryls with alkynes to
polycyclic heteroaromatics6a and Itami et al. reported a Pd-
catalyzed homoannulation of arylacetylenes toward synthesis of
dibenzopentalenes.6b
The twisted π-conjugated molecules of 9,9′-bifluorenylidene
(9,9′BF) and its derivatives readily accept one electron to fulfill a
14-π-electron system, which were found to be useful non-
fullerene-electron-accepting materials in bulk-heterojunction
solar cells.8 In general, 9,9′BF derivatives could be synthesized
from fluorenones through multiple steps,9 and a new Pd-
catalyzed double cross-coupling reaction of 9-(dibromomethy-
lene)-9H-fluorene with 9-stannafluorene has been developed by
Hiyama et al.10 Taking those pioneering C−H functionalization
methods into consideration and our continuous interest in Pd-
The unexpected mechanistic evidence indicates that the present
transformation is in sharp contrast with the previously reported
hydroarylation2−6 and it seems to proceed through an unusual
mechanism involving dual C−H activation followed by
carbopalladation with a C−C triple bond.
Our optimization results are summarized in Table 1. The
reaction of bis-biphenyl alkyne 1a with PdCl2 as a catalyst in N,N-
dimethylacetamide (DMAc) at 80 °C for 12 h afforded only 3%
of the corresponding products cis-2a and trans-2a (∼1:1) (entry
1). On the basis of the recently reported oxidative dehydrogen-
ation C−H coupling conditions,12 various oxidants have been
examined. The oxidants that were commonly used in Pd-
catalyzed transformations, such as K2S2O8, Ag2O, o-chloranil,
CuCl2, and PhI(OAc)2, were almost totally inactive (entries 2−
6). To our delight, the use of activated MnO2 (2 equiv) as an
oxidant drastically increased the reactivity, producing the
corresponding products 2a in 43% yield together with the
recovered 1a in 51% yield (entry 7). Indeed, during the reaction
using the PdCl2 catalyst without using oxidants as shown in entry
1, we observed some amounts of palladium black precipitates and
the reaction mixture showed acidity, which indicate the
generation of Pd(0) species and hydrochloric acid.13 We
assumed that MnO2 could oxidize the Pd(0) species to the
active Pd(II) species in the presence of in situ generated HCl,
which may accelerate the catalytic cycle. Moreover, we were
Received: April 1, 2014
Published: June 20, 2014
© 2014 American Chemical Society
9540
dx.doi.org/10.1021/ja503252k | J. Am. Chem. Soc. 2014, 136, 9540−9543

Journal of the American Chemical Society
Communication
a
Table 1. Optimization of Reaction Conditions
Table 2. PdCl2-Catalyzed Annulation of Various Bis-biphenyl
Alkynes
a
oxidant
(2 equiv)
additive
(10 mol %)
yield
b
entry Pd catalyst (10 mol %)
(%)
1
PdCl2
none
none
3
5
4
0
0
2
PdCl2
K2S2O8
Ag2O
none
3
PdCl2
none
4
PdCl2
o-chloranil
CuCl2
none
5
PdCl2
none
6
PdCl2
PhI(OAc)2
MnO2
MnO2
MnO2
MnO2
MnO2
MnO2
MnO2
none
trace
7
PdCl2
none
43
8
PdCl2
PivOH
PivOH
PivOH
PivOH
PivOH
PivOH
PivOH
PivOH
82
9
PdBr2
69
10
11
12
13
14
15
Pd(OAc)2
Pd(OPiv)2
Pd(CH3CN)4(BF4)2
Pd2(dba)3
PdCl2
12
4
5
3
c
MnO2
98 (93)
d
c
e
PdCl2
MnO2
87
a
Reaction conditions: 1a (0.2 mmol), Pd catalyst (10 mol %), oxidant
(2 equiv), DMAc (0.5 M), under a N2 atmosphere, 80 °C for 12 h.
b
1H NMR yield determined using CH2Br2 as an internal standard. The
c
isolated yields are shown in parentheses. MnO2 (3 equiv) was used.
d
e
The reaction carried out at rt for 24 h. The ratio of cis-2a and trans-
2a is 4:1.
pleased to find that the use of pivalic acid (PivOH, 10 mol %) as a
cocatalyst further improved the chemical yield of 2a to 82%
(entry 8), which strongly indicates the involvement of a pivalate-
assisted C(sp2)−H bond cleavage. It should be mentioned that
other oxidants used in entries 2−6 were still inefficient in the
presence of PivOH, supporting the important role of the MnO2
oxidant.13 Although other palladium catalysts, such as Pd(OAc)2,
Pd(OPiv)2, Pd(CH3CN)4(BF4)2, and Pd2(dba)3, were inactive,
the PdBr2 catalyst exhibited good catalytic activity, affording 2a in
70% yield, indicating an efficient combination of palladium
halides with the MnO2 oxidant (entries 9−13). Other transition
metals, such as NiCl2, PtCl2, and RhCl(PPh3)3, were totally
inactive for the present transformation (see Supporting
Information (SI)). The use of 3 equiv of MnO2 further improved
the isolated yield of 2a to 93% (entry 14). It is noted that the
product 2a was obtained as a 1:1 ratio of cis- and trans-isomers at
80 °C under the above-mentioned conditions (entries 1−14).
The reaction also could carry out at rt under the prolonged
reaction time (24 h) to give 2a in 87% yield with a 4:1 mixture of
cis- and trans-isomers (entry 15), in which the predominant
isomer cis-2a was isomerized at rt (3 days) and at 80 °C (12 h) to
give a 2:1 and 1:1 mixture of cis-2a and trans-2a, respectively (SI,
Figure S1). These results suggest that the reaction should
proceed in a cis-annulation manner followed by a cis to trans
isomerization. Finally, it should be noted that the use of the
freshly activated MnO2 oxidant is important to achieving a high
chemical yield of 2a. Overall, it was concluded that the use of a
PdCl2/PivOH (10 mol %) catalyst system combined with the
activated MnO2 oxidant was optimal for the successful
implementation of the present catalytic transformation.
a
Reaction conditions: 1 (0.2 mmol), PdCl2 (10 mol %), PivOH (10
mol %), MnO2 (3 equiv), under a N2 atmosphere, 80 °C for 12 h.
b
c
Isolated yields after silica gel chromatography. The reaction time is
d
e
24 h. A 4:1 mixture of 2j and 2k was obtained. A 1.9:1 mixture of 2l
and 2l′ was obtained.
methyl-[1,1′-biphenyl]-2-yl)ethyne (1b) without a substituent
on the biphenyl rings afforded the corresponding product 9,9′BF
(2b) in 92% yield (entry 1). The product 2b was unambiguously
confirmed by H and 13C NMR comparing with the reported
1
literature.8c Bis-biphenyl alkynes 1c−e having an electron-
withdrawing group, such as aldehyde, ester, and fluorine, were
well tolerated, giving the corresponding 9,9′BF derivatives 2c−e
in good to high yields (entries 2−4). The reactions with bis-
biphenyl alkynes 1f−k having an electron-donating group, such
as methyl, methoxy, and N,N-diphenylamine, produced higher
yields of the corresponding products 2f−j compared with that of
Optimal conditions showed high compatibility and efficiency
with various bis-biaryl alkynes for synthesis of a variety of 9,9′BF
derivatives (Table 2). Under the standard conditions, 1,2-bis(4′-
9541
dx.doi.org/10.1021/ja503252k | J. Am. Chem. Soc. 2014, 136, 9540−9543

Journal of the American Chemical Society
Communication
the substrates 1c−e (entries 5−10), in which 1j bearing a methyl
group at the meta-position afforded the corresponding products
2j and 2k in 88% yield with a 4:1 ratio (entry 9, SI, Figure S2).
Although the 2-naphthyl-substituted biaryl alkyne 1l showed
high reactivity, the product was obtained as a 1.9:1 mixture of
regiosiomers 2l and 2l′ (entry 11, SI, Figure S2). The recent
interest in heteroaromatic-incorporated 9,9′BF derivatives as a
key unit in low band gap electron donor polymers for organic
photovoltaics14 led us to examine the hetroaromatic-containing
bis-biaryl alkynes. Both benzothiophene and benzofuran
substituted bis-biaryl alkynes 1m and 1n exhibited high stability
under our acidic conditions, furnishing the anticipated products
2m and 2n in 92% and 81% yields, respectively (entries 12 and
13).
the starting material was recovered, indicating that the potential
pathway of the cation radical dimerization16 of 4a could be
excluded (SI, Scheme S1). It should be emphasized that the
reaction of bis-biphenyl alkyne 1b under the Gevorgyan
conditions5a did not afford any of the desired products and the
Jiao6b and Itami’s conditions6b for the reactions of 1a were almost
inactive (SI, Schemes S2 and S3), indicating that our catalytic
system is unique for the formation of 9,9′BF derivatives from bis-
biaryil alkynes.
To further understand the mechanistic insight, the deuterium
isotope experiments were performed. Under the standard
conditions, the reaction of the deuterated substrate 1k′ produced
the corresponding product 2j′ as a mixture of cis- and trans-
isomers in almost quantitative yield without observation of a H−
D exchange, indicating the irreversible C−H bond cleavage (SI,
Scheme S4). An intermolecular competing reaction of 1k and 1k′
was also studied (SI, Scheme S5). The product 2j and the
deuterated product 2j′ were obtained with similar kinetic isotope
effects (KIEs) of 1.7 and 1.6 at 80 °C (15 min) and rt (2.5 h),
respectively. Considering the cleavage of two C−D bonds in the
substrate 1k′, the fact that the C−H bond cleavage occurs during
the rate-determining step cannot be fully explained by this KIE
value. Instead, this result implies the involvement of alkyne- or
pivalate-assisted C−H bond activation.
The bis-biphenyl alkynes 1o and 1p having two methoxy
groups and two trifluoromethyl groups at both 1,2-biphenyl
rings, respectively, reacted smoothly to form a mixture of cis- and
trans-products in high yields. (eq 1). Irrespective of the electron-
Overall, the following results have been obtained exper-
imentally: (a) the reaction proceeds in a cis-annulation manner;
(b) the formation of vinylpalladium intermediate is unlikely; (c)
both electron-withdrawing and -donating groups are highly
compatible; (d) products 2 and 5a are unavailable using the
reported dual C−H activation conditions, which implied that the
current reaction should undergo a different pathway compared
with the related reactions.2−6 Based on the experimental results
and taking into consideration the literature on C−H arylations
assisted by σ-chelating directing groups,12 we propose a
mechanism involving biarylpalladium intermediate formation
via alkyne-directed dual C−H activation.5b A plausible reaction
mechanism is illustrated in Scheme 2. Initially, PdCl2 coordinates
donating and -withdrawing groups on the biphenyl rings, the
substrates 1o and 1p produced the cis- and trans-isomers of 2o
and 2p in high yields with a ratio of 1:1.1 and 1.5:1 at 80 °C,
respectively. Interestingly, the reaction of 1p took place at rt
within 20 h by using a large amount of PdCl2 and PivOH to give a
mixture of cis-2p and trans-2p in 85% yield with the former as a
predominant product (5:1). The cis-2p isomer could be isolated
by silica gel chromatography, which slowly isomerized to trans-
2p after 24 h in solution to give a mixture of isomers.15 The
remarkable reactivity of the alkyne 1p having two strong
electron-withdrawing groups on the aromatic rings strongly
contradicts with the typical electrophilic hydroarylation of
alkynes which generally proceeds with the electron-rich aromatic
rings.2−4 In addition, the selectivity of the cis-2p isomer at rt
implied the involvement of a cis-cyclization pathway in this
transformation.
Scheme 2. Proposed Reaction Mechanism
We next examined the annulation of o-alkynyl biphenyl under
our reaction conditions to probe the possible carbopalladation
intermediate. However, as shown in eq 2, the reaction of 2-
with the C−C triple bond of 1b to produce Pd-π-complex A
which may undergo a direct ortho-C−H bond insertion into the
adjacent phenyl ring assisted by PivOH to form arylpalladium
complex B.5,6b Subsequently, the intramolecular PivOH-assisted
insertion of the complex B into the second ortho-C−H bond may
take place prior to carbopalladation of the triple bond, affording
the cyclized biarylpalladium complex C.12 Alternatively, the
simultaneous double ortho-C−H activation of the intermediate A
through a PivOH-assisted transition state to form the complex C
(phenylethynyl)-1,1′-biphenyl (3a) afforded an unexpected
dimerized fluorenylidene product 5a in good yield without
formation of the desired fluorene product 4a which was expected
to be formed through protonation of a vinylpalladium
intermediate as reported by Gevorgyan et al.5a Furthermore,
the reaction of 4a prepared following Gevorgyan’s conditions
from 3a under our standard conditions did not proceed at all and
9542
dx.doi.org/10.1021/ja503252k | J. Am. Chem. Soc. 2014, 136, 9540−9543

Journal of the American Chemical Society
Communication
(4) Mamane, V.; Hannen, P.; Furstner, A. Chem.Eur. J. 2004, 10,
̈
also can be considered. Next, the intramolecular alkyne
carbopalladation of the biarylpalladium complex C affords the
six-membered palladacycle D. Subsequent reductive elimination
of the intermediate D gives the corresponding product 2b and
the Pd(0) species. The MnO2 oxidant proved to be an efficient
oxidant for regeneration of the active PdCl2 catalyst from the
Pd(0) species in the presence of the in situ generated HCl,13
which is a key point for the successful implementation of the
present catalytic transformation. The PivOH cocatalyst accel-
erates the ortho-C−H bond cleavage through the formation of
the pivalate-promoted transition state.11,17 Following this
proposed mechanism, the unexpected product 5a in eq 2 should
be formed through the intermolecular alkyne directed dual C−H
activation to produce the biarylpalladium analogue,12 followed
by an intramolecular carbopalladation (SI, Scheme S6).18 This
pathway may explain the reason why the expected product 4a
cannot be formed under our reaction conditions.
In summary, we have developed a novel and efficient Pd-
catalyzed dual C−H activation/annulation transformation of bis-
biaryl alkynes under mild reaction conditions. The present
reaction provides a new and general synthetic methodology for
construction of various new 9,9′BF derivatives with a broad range
of functional groups. The use of the PdCl2 catalyst combined
with the MnO2 oxidant and PivOH additive is vital for the
accomplishment of the catalytic cycle sufficiently. The
experimental results clearly indicate that a novel dual C−H
activation followed by an annulation with alkynes may be
operating in the current transformation, which is distinct from
the previously reported pathways. Further study of the
mechanistic details and application of new 9,9′BF derivatives
as n-type materials for optoelectronic devices is in progress.
4556.
(5) (a) Chernyak, N.; Gevorgyan, V. J. Am. Chem. Soc. 2008, 130, 5636.
(b) Involvement of a biarylpalladium intermediate forming through an
alkyne-directed C−H activation was proposed as a minor pathway; see:
Chernyak, N.; Gevorgyan, V. Adv. Synth. Catal. 2009, 351, 1101.
(6) For Pd-catalyzed arene/alkyne annulation via dual C−H activation,
see: (a) Shi, Z.; Ding, S.; Cui, Y.; Jiao, N. Angew. Chem., Int. Ed. 2009, 48,
7895. (b) Maekawa; Segawa, Y.; Itami, K. Chem. Sci. 2013, 4, 2369.
(c) Wu, Y.-T.; Huang, K.-H.; Shin, C.-C.; Wu, T.-C. Chem.Eur. J.
2008, 14, 6697. For Rh-catalyzed arene/alkyne annulation via dual C−
H activation, see: (d) Umeda, U.; Tsurugi, H.; Satoh, T.; Miura, M.
Angew. Chem., Int. Ed. 2008, 47, 4019. (e) Iitsuka, T.; Hirano, K.; Satoh,
T.; Miura, M. Chem.Eur. J. 2014, 20, 385.
(7) For related double cyclization of arenylalkynes, see: (a) Rahman, S.
M. A.; Sonoda, M.; Itahashi, K.; Tobe, Y. Org. Lett. 2003, 5, 3411.
(b) Fukazawa, A.; Karasawa, T.; Zhang, H.; Minemura, K.; Camacho, C.;
Wang, J.; Irle, S.; Yamaguchi, S. Angew. Chem., Int. Ed. 2013, 52, 10519.
(c) Yamaguchi, S.; Swager, T. M. J. Am. Chem. Soc. 2001, 123, 12087.
(d) Li, C.-W.; Wang, C.; Liao, H.-Y.; Chaudhuri, R.; Liu, R.-S. J. Org.
Chem. 2007, 72, 9203. (e) Chaudhuri, R.; Hsu, M.-Y.; Li, C.-W.; Wang,
C.; Chen, C.-J.; Lai, C. K.; Chen, L.-Y.; Liu, S.-H.; Wu, C.-C.; Liu, R.-S.
Org. Lett. 2008, 10, 3053. (f) Chen, T.-A.; Liu, R.-S. Org. Lett. 2011, 13,
4644. (g) Dou, C.; Saito, S.; Gao, L.; Matsumoto, N.; Karasawa, T.;
Zhang, H.; Fukazawa, A.; Yamaguchi, S. Org. Lett. 2013, 15, 80.
(8) (a) Brunetti, F. G.; Gong, X.; Tong, M.; Heeger, A. J.; Wudl, F.
Angew. Chem., Int. Ed. 2010, 49, 532. (b) Park, O. Y.; Kim, H. U.; Kim, J.-
H.; Park, J. B.; Kwak, J.; Shin, W. S.; Yoon, S. C.; Hwang, D.-H. Sol.
Energy Mater. Sol. 2013, 116, 275. (c) Kim, H. U.; Kim, J.-H.; Suh, H.;
Kwak, J.; Kim, D.; Grimsdale, A. C.; Yoon, S. C.; Hwang, D.-H. Chem.
Commun. 2013, 49, 10950.
(9) Yip, Y. C.; Wang, X.-J.; Ng, D. K. P; Mak, T. C. W; Chiang, P.; Luh,
T.-Y. J. Org. Chem. 1990, 55, 1881. (b) Minabe, M.; Yamazaki, A.; Imai,
T.; Takanezawa, T.; Karikomi, M. Bull. Chem. Soc. Jpn. 2006, 11, 1758.
(c) Assadi, N.; Pogodin, S.; Agranat, I. Eur. J. Org. Chem. 2011, 6773.
(d) Brunetti, F. G.; Varotto, A.; Batara, N. A.; Wudl, F. Chem.Eur. J.
2011, 8604.
(10) Shimizu, M.; Nagao, I.; Kiyomoto, S.; Hiyama, T. Aust. J. Chem.
2012, 65, 1277.
(11) Zhao, J.; Oniwa, K.; Asao, N.; Yamamoto, Y.; Jin, T. J. Am. Chem.
Soc. 2013, 135, 10222.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures and characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
(12) For recent reviews of Pd-catalyzed dehydrogenative aryl−aryl
coupling reactions, see: (a) Liu, C.; Zhang, H.; Shi, W.; Lei, A. Chem.
Rev. 2011, 111, 1780. (b) Yeung, C. S.; Dong, V. M. Chem. Rev. 2011,
111, 1215. (c) Yamaguchi, J.; Yamaguchi, A. D.; Itami, K. Angew. Chem.,
Int. Ed. 2012, 51, 8960.
AUTHOR INFORMATION
Corresponding Author
tjin@m.tohoku.ac.jp
■
Notes
(13) It is known that the redox reaction of MnO2 with HCl produces
Cl2, MnCl2, and H2O, and PdCl2 can be prepared from the reaction of
Pd(0) with Cl2 in the presence of HCl; see: Handbook of Preparative
Inorganic Chemistry; Brauer, G., Ed.; Academic Press: New York,
London, 1963. Consequently, we propose that, in this reaction, the
reduced Pd(0) could be oxidized by MnO2 with HCl to regenerate
PdCl2.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a Scientific Research (B) from Japan
Society for Promotion of Science (JSPS) (No. 25288043), and
World Premier International Research Center Initiative (WPI),
MEXT, Japan.
(14) Chiu, C. Y.; Wang, H.; Brunetti, F. G.; Wudl, F.; Hawker, C. J.
Angew. Chem., Int. Ed. 2014, 53, 3996.
(15) Gault, I. R.; Ollis, W. D.; Sutherland, I. O. J. Chem. Soc., Chem.
Commun. 1970, 269.
(16) (a) Mattes, S. L.; Farid, S. J. Am. Chem. Soc. 1986, 108, 7356.
(b) Kim, K. S.; Son, S. H.; Joo, Y. H.; Jung, D. I.; Hahn, C. S. Chem. Lett.
1987, 2251.
(17) (a) Lafrance, M.; Gorelsky, S. I.; Fagnou, K. J. Am. Chem. Soc.
2007, 129, 14570. (b) Rousseaux, S.; Gorelsky, S. I.; Chung, B. K. W.;
Fagnou, K. J. Am. Chem. Soc. 2010, 132, 10692.
(18) A referee pointed out an alternative plausible pathway for the
formation of 5a. It may be produced through the Pd-catalyzed
disproportionation mechanism; see: Masui, K.; Ikegami, H.; Mori, A.
J. Am. Chem. Soc. 2004, 126, 5074.
REFERENCES
■
(1) For recent reviews, see: (a) Transition-Metal-Mediated Aromatic
Ring Construction;: Tanaka, K., Ed.; Wiley: New York, 2013. (b) Jin, T.;
Zhao, J.; Asao, N.; Yamamoto, Y. Chem.Eur. J. 2014, 20, 3554.
(2) For selected hydroarylation reviews, see: (a) Nevado, C.;
Echavarren, A. M. Synthesis 2005, 167. (b) Hashmi, A. S. K. Chem.
Rev. 2007, 107, 3180. (c) Furstner, A.; Davies, P. W. Angew. Chem., Int.
Ed. 2007, 46, 2. (d) Jimenez-Nuuez, E.; Echavarren, A. M. Chem. Rev.
̈
́
́
̃
2008, 108, 3326. (e) Patil, N. T.; Yamamoto, Y. Chem. Rev. 2008, 108,
3395. (f) Yamamoto, Y.; Gridnev, I. D.; Patil, N. T.; Jin, T. Chem.
Commun. 2009, 5075.
(3) (a) Jia, C.; Piao, D.; Oyamada, J.; Lu, W.; Kitamura, T.; Fujiwara, Y.
Science 2000, 287, 1992. (b) Jia, C.; Piao, D.; Kitamura, T.; Fujiwara, Y. J.
Org. Chem. 2000, 65, 7516.
9543
dx.doi.org/10.1021/ja503252k | J. Am. Chem. Soc. 2014, 136, 9540−9543