Palladium(0)-Catalyzed Methylcyclopropanation of Norbornenes with Vinyl Bromides and Mechanism Study

Article abstract of DOI:10.1021/acs.orglett.5b01603

An unusual methylcyclopropanation from [2 + 1] cycloadditions of vinyl bromides to norbornenes catalyzed by Pd(OAc)₂/PPh₃ in the presence of CH₃ONa and CH₃OH has been established. A methylcyclopropane subunit was installed by a 3-fold domino procedure involving a key protonation course. Preliminary deuterium-labeling studies revealed that the proton came from methyl of CH₃OH and also exposed an additional hydrogen/deuterium exchange process. These two proton-concerned reactions were fully chemoselective.

Full text of DOI:10.1021/acs.orglett.5b01603

Letter
pubs.acs.org/OrgLett
Palladium(0)-Catalyzed Methylcyclopropanation of Norbornenes
with Vinyl Bromides and Mechanism Study
Jiangang Mao,†,‡ Hujun Xie,§ and Weiliang Bao*,†
†Department of Chemistry, Zhejiang University, Hangzhou 310028, Zhejiang, P.R. China
‡School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, Jiangxi, P.R. China
§School of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310035, Zhejiang P.R. China
S
* Supporting Information
ABSTRACT: An unusual methylcyclopropanation from [2 +
1] cycloadditions of vinyl bromides to norbornenes catalyzed
by Pd(OAc)2/PPh3 in the presence of CH3ONa and CH3OH
has been established. A methylcyclopropane subunit was
installed by a 3-fold domino procedure involving a key
protonation course. Preliminary deuterium-labeling studies
revealed that the proton came from methyl of CH3OH and
also exposed an additional hydrogen/deuterium exchange
process. These two proton-concerned reactions were fully
chemoselective.
Scheme 1. Protonation and H/D Exchange in Transition-
Metal-Catalyzed Coupling Reaction
s a significant structural motif, the cyclopropane skeleton is
Afound in numerous biomolecules and pharmaceutical drugs,
such as pyrethrum,1 FR-900848,2 lactobacillic acid,3 and
tranylcypromine.4 Cyclopropanation is always a highly active
area of organic chemistry for both theoretical and practical
purposes5 and has attracted tremendously attention from organic
chemists. Among the myriad methods available for constructing
the cyclopropane scaffold,5,6 transition-metal-catalyzed C−H or
C−C bond activation is undoubtedly a fascinating method-
ology,7 except for carbene/carbenoid cycloaddition,8 Simmons−
Smith reaction,9 Michael-initiated ring closure (MIRC),10 and
cycloisomerization.11 The cyclopropanation via the coupling of
norbornenes with organoboron reagents or alkynes has been
reported.12 The intermolecular cyclopropanation of halohydro-
carbon generally underwent a carbene intermediate.8a,b How-
ever, transition-metal-catalyzed cyclopropanation of halohydro-
carbon with alkenes via a noncarbene mechanism remains
underdeveloped.13 Herein, we report the first example of
Pd(OAc)2/PPh3-catalyzed methylcyclopropanation of bromos-
tyrenes with norbornenes via [2 + 1] cycloaddition involving a
methylene protonation and an additional H/D exchange with
CD3OD (Scheme 1).
In a few cases, the protonation reaction was accompanied by
transition-metal-catalyzed coupling reactions. The proton
sources may be materials such as alcohol and water, etc.14 The
alkoxy group of alcohol can afford a proton via coordination with
transition metal,15 and hydroxyl can also initiate an H/D
exchange by transition-metal-catalyzed C−H activation.16
However, to the best of our knowledge, transition-metal-
catalyzed coupling reactions involving both protonation and
H/D exchange reactions have not been reported.
carried out successfully using K2CO3 and Cs2CO3 as base,
respectively, in our laboratory.13a,17 While further studying the
selectivity of the above reactions, we found methylcyclopropane
product in the presence of CH3ONa as base. The preliminary
evaluation on this result revealed that the norbornenylpalladium
imtermediate grabbed a proton from the reaction system.
However, subsequent reaction mechanism research demon-
strated that the methylcyclopropanation process underwent a
protonation and an additional H/D exchange with CD3OD. Two
kinds of deuterium atoms from CD3OD were all embedded
chemoselectively in the different positions of norbornene-fused
methylcyclopropane derivatives (Scheme 1).
The interesting domino [2 + 1] cycloaddition reaction
prompted us to investigate the reaction parameters. (Z)-1-(2-
Bromovinyl)-4-methoxybenzene 1a and endo-N-(p-tolyl)-
norbornenesuccinimide 2a were employed as model substrates
to optimize the reaction conditions. The results are summarized
in the Supporting Information (Table SI1). Previous studies
The Pd(0)-catalyzed methylenecyclopropanation and bisme-
thenylcyclobutanation of bromostyrenes with norbornenes were
Received: June 1, 2015
Published: July 21, 2015
© 2015 American Chemical Society
3678
DOI: 10.1021/acs.orglett.5b01603
Org. Lett. 2015, 17, 3678−3681

Organic Letters
Letter
showed that base was a key reaction parameter, so different bases
such as K2CO3, Cs2CO3, CsOAc, C2H5ONa, and CH3ONa were
reviewed first. It affected both product yields and product
categories. When 2.0 and 3.0 equiv of Cs2CO3 was used as base
and 0.2 mL of CH3OH was added, the desired product 3aa was
isolated, respectively, in 31% and 78% yields (see Table SI1,
entries 2 and 3). When K2CO3 was employed as base, the
reaction gave 4aa as product but not 3aa (92% yield, Table SI1,
entry 1).13a Even if 4.0 or 6.0 equiv of CsOAc was used as base,
4aa was still the main product (72% and 75% yield, Table SI1,
entries 4 and 5). C2H5ONa afforded 85% yield product 3aa. The
[2 + 1] cycloaddition afforded methylcyclopropane 3aa with the
best yield in the presence of 3.0 equiv of CH3ONa (96% yield,
entry 10).
Scheme 2. Substrate Scope of Pd-Catalyzed
Methylcyclopropanation of Norbornenes with (Z)-Vinyl
a
Bromides
After CH3ONa was identified as the best base, other reaction
parameters were optimized using it. Several Pd precatalysts were
screened (Table SI1, entries 10−13). Using Pd(dppf)Cl2 as the
precatalyst, 3aa was obtained in 83% yield (Table SI1, entry 13),
while PdCl2 and Pd(PPh3)4 delivered the desired products in
52% and 74% yields, respectively (Table SI1, entries 11 and 12).
Then the ligands dppe, BINAP, TMOPP, and TCHP were
screened and afforded 3aa in 74%, 70%, 91%, and 68% yields,
respectively (Table SI1, entries 6−9). The effects of solvent and
additive were also investigated. The reaction could be conducted
successfully in methanol (63% yield, Table SI1, entry 18). Other
solvents, such as CH3CN, dioxane, DMSO, and DMF, were also
suitable for the reaction but only afforded 3aa in low or moderate
yields (43%−66% yield, Table SI1, entries 14−17). Subse-
quently, additives such as C2H5OH, PhCH2OH, and Cl-
(CH2)2OH were also surveyed; methylcyclopropane 3aa was
obtained in 42%, 61%, and 72% yields, respectively, in the
presence of Cs2CO3 due to the different pKa and steric hindrance
of the alcohols (Table SI1, entries 21−23). The loading of 1.0
mL of CH3OH reduced the yield of 3aa to 75% (Table SI1, entry
20). When the reaction was carried out in the absence of
CH3OH, the result was not ideal and only afforded a trace of the
desired product (Table SI1, entry 19). The best reaction
temperature is at 110 °C (96% yield, Table SI1, entry 10). The
yields decreased to 91% and 66%, respectively, when the
reactions were carried out at 120 and 90 °C (Table SI1, entries 24
and 25). The best yield of methylcyclopropane 3aa was obtained
when the model reaction was catalyzed by Pd(OAc)2/PPh3, 3.0
equiv of CH3ONa was employed as base, and 0.2 mL of CH3OH
was used as the additive in toluene (96% yield, Table SI1, entry
10).
With the optimized reaction conditions in hand, some
representative substrates were employed to investigate the
scope and generality of the [2 + 1] cycloaddition domino
reaction, as shown in Scheme 2. (Z)-2-Bromovinylarenes bearing
electron-donating (3-Me, 4-Me, and 4-MeO) groups on the
benzene core afforded the corresponding methylcyclopropane
derivatives 3 in excellent yields (Scheme 2, 3aa, 3ca−da, 3db,
3ac, 3cc−dc, 3ad, 3cd−dd), while (Z)-2-bromovinylarenes
bear-ing electron-withdrawing groups (2-Cl, 3-Cl, 4-Cl, and 4-F)
on the benzene ring provided products 3 in good to high yields
(Scheme 2, 3ea−ha, 3fb, 3hb, 3hc, 3hd). The para-substituted
vinylarenes provided methylcyclopropane products 3ca, 3ea,
3cc, and 3cd in higher yield (Scheme 2, 95%, 89%, 85% and 83%
yield) owing to much smaller steric hindrance compared with the
corresponding meta-substituted vinylarenes (3da, 3fa, 3dc, and
3dd; 91%, 82%, 82%, and 81% yield). The reaction scope was
further extended to aliphatic (Z)-1-bromoalkenes 1i successfully,
a
Reaction conditions unless otherwise noted: 1 (0.55 mmol), 2 (0.5
mmol), Pd(OAc)2 (0.05 mmol), PPh3 (0.11 mmol), CH3ONa (1.5
mmol), toluene (2.0 mL), CH3OH (0.2 mL), 110 °C, 12 h in sealed
tube. Isolated yields are shown. CH3ONa (1.0 mmol). Reaction
conditions: 1 (0.5 mmol), 2 (0.6 mmol), Pd(OAc)2 (0.05 mmol),
PPh3 (0.11 mmol), CH3ONa (2.0 mmol), toluene (2.0 mL).
b
c
and afforded methylcyclopropanation products 3ia and 3ib in
71% and 76% yields, respectively.
After the scope of the (Z)-2-bromovinylarenes was screened,
another coupling partner, norbornene derivatives, was inves-
tigated. endo-N-Isobutylnorbornenesuccinimide 2b was coupled
smoothly with (Z)-vinyl bromides to give corresponding
products 3db, 3fb, and 3hb−ib in good to high yields under
the optimized reaction conditions. Norbornene itself 2c also
provided the desired methylcyclopropanes with good yields in
the presence of 4.0 equiv of CH3ONa (Scheme 2, 3ac, 3cc−dc,
3hc). Functionalized norbornene derivatives such as (1R,4S)-
1,4-dihydro-1,4-methanonaphthalene-5,8-diyl diacetate success-
fully produced the corresponding methylcyclopropanes in good
to excellent yields (Scheme 2, 3ad, 3cd, 3dd, 3hd). Cyclohexene
was also employed as alkene to carry out the [2 + 1]
cycloaddition reaction, however, the reaction did not proceed
smoothly. The structure of products was further confirmed
unambiguously by X-ray crystallography of 3da (see the SI,
Figure S1). The formed methylcyclopropane subunit took the
exo-face of norbornane.
Subsequently, (E)-2-bromovinylarene substrates (E)-1 were
investigated, and the corresponding methylcyclopropane prod-
3679
DOI: 10.1021/acs.orglett.5b01603
Org. Lett. 2015, 17, 3678−3681

Organic Letters
Letter
ucts 3aa, 3ba, 3ea, 3ha, 3hb, and 3bd were obtained under the
same reaction conditions (Scheme 3, 71%, 63%, 52%, 56%, 51%,
an α-deuterium of one carbonyl and a methylene-deuterated of
benzyl was produced successfully in 45% yield (Scheme 4, eq 4).
The α-H of carbonyl tended to undergo hydrogen/deuterium
exchange with CH3OD or CD3OD in the presence of base owing
to its relatively small pKa. In order to see whether the H/D
exchange is caused by its acidity, deuterium-labeling experiments
of the 2e and 3A were carried out, respectively, in the absence of
Pd(OAc)2 and PPh3, only using Cs2CO3 as base and CH3OD as
additive. However, no product with an α-deuterium of carbonyl
was observed. This meant that the H/D exchange of the α-
position of carbonyl is not because of its acidity, but the catalytic
cycle may have a key influence on the H/D exchange.
Scheme 3. Substrate Scope of Pd-Catalyzed
Methylcyclopropanation of Norbornenes with (E)-Vinyl
a
Bromides
On the basis of the current experimental results and related
precedents,13−16,20 a postulated mechanism was proposed
(Figure 1). The oxidative addition of palladium(0) species to
a
Reaction conditions unless otherwise noted: (E)-1 (0.55 mmol), 2
(0.5 mmol), Pd(OAc)2 (0.05 mmol), PPh3 (0.11 mmol), CH3ONa
(1.5 mmol), toluene (2.0 mL), CH3OH (0.2 mL), 110 °C, 12 h in
b
sealed tube. Isolated yields are shown. Reaction conditions: 1 (0.5
mmol), 2 (0.6 mmol), Pd(OAc)2 (0.05 mmol), PPh3 (0.11 mmol),
CH3ONa (2.0 mmol), toluene (2.0 mL), CH3OH (0.2 mL).
and 59% yields). Obviously, the (Z)-2-bromovinylarene
substrates provided better yields than that of (E)-ones. It may
be that the benzene ring of (Z)-2-bromovinylarene stabilizes the
norbornenylpalladium intermediate via favorable interaction
between the π system of benzene ring and Pd center.18 However,
(E)-2-bromovinylarene cannot exert the same stabilizing role
because it lacks such space advantage.
Figure 1. Proposed reaction mechanism for the palladium-catalyzed
methylcyclopropanation.
Where did the additional hydrogen atom came from? In order
to answer the question, deuterium-labeling experiments were
carried out using (Z)-(2-bromovinyl)benzene 1b and endo-N-(p-
methoxy)phenylnorbornenesuccinimide 2e as model substrates
(Scheme 4).19 First, when toluene-d8 was used as solvent and
(Z)-bromostyrene derivative 1 produced (Z)-styrylpalladium-
(II) bromide I. Subsequently, the syn addition of I to norbornene
2 at the exo-face generated norbornenyl palladium complex II.
Palladium complexes might exist in an equilibrium between
neutral and cationic species.21 The polar solvent could stabilize
the cationic species and the polarity of solvent toluene would be
increased in the presence of CD3OD, thus rendering a cationic
palladium species III as the major intermediate, which was called
the outer form.22 Subsequently, “bridging” palladium complex IV
was generated.23 Thus, the corresponding norbornene fragment
became more positively charged to prompt the α-H/D exchange
in the presence of base, while CD3OD coordinated to the Pd(II)
and provided a D from OD group. The olefin of the intermediate
VI coordinated to the Pd center, which was followed by an
insertion reaction to produce cyclopropanepalladium intermedi-
ate VII. The selective β-H elimination of VII yielded Pd−D
complex VIII and released methanal.24 Reductive elimination of
complex VIII produced methylcyclopropane derivatives 3 and
regenerated Pd(0).
Scheme 4. Deuterium-Labeling Studies
In conclusion, we have developed a novel Pd(OAc)2/PPh3-
catalyzed [2 + 1] cycloaddition domino reaction of vinyl
bromides to norbornene derivatives involving a protonation
process and an additional H/D exchange from CD3OD. By this
protocol, a methylcyclopropane subunit was installed via the 3-
fold domino reaction including Heck-type reaction/C−C bond
activation/protonation. Preliminary deuterium-labeling studies
demonstrated where the proton came from. This method is
unusual, but practical, which complemented the classic methods
for the fast synthesis of multiple substituted methylcyclopropane
derivatives. Further investigation of the reaction mechanism is
underway.
CH3OH was employed as additive, nondeuterated methylcyclo-
propane 3A was obtained in 73% yield (Scheme 4, eq 1). Second,
when CD3OH was employed as the additive and toluene was
used as solvent, benzyl methylene-deuterated methylcyclopro-
pane 3B was successfully isolated in 55% yield (Scheme 4, eq 2).
Subsequently, the reaction was investigated again using CH3OD
as additive and toluene as solvent, methylcyclopropane 3C of α-
deuterium of one carbonyl was obtained in 62% yield (Scheme 4,
eq 3). Finally, when the reaction was carried out in toluene using
CD3OD as additive, another methylcyclopropane 3D with both
3680
DOI: 10.1021/acs.orglett.5b01603
Org. Lett. 2015, 17, 3678−3681

Organic Letters
Letter
(14) (a) Kuwabe, S.; Torraca, K. E.; Buchwald, S. L. J. Am. Chem. Soc.
2001, 123, 12202. (b) Tseng, N.-W.; Mancuso, J.; Lautens, M. J. Am.
Chem. Soc. 2006, 128, 5338. (c) Dash, P.; Janni, M.; Perunchera-lathan,
S. Eur. J. Org. Chem. 2012, 2012, 4914.
(15) (a) Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc.
1997, 119, 3395. (b) Torraca, K. E.; Kuwabe, S.-I.; Buchwald, S. L. J. Am.
Chem. Soc. 2000, 122, 12907.
ASSOCIATED CONTENT
* Supporting Information
Experimental details, characterization data, full spectroscopic
data for all new compounds, and X-ray crystallographic data. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.orglett.5b01603.
■
S
(16) (a) Matsukawa, Y.; Mizukado, J.; Quan, H.; Tamura, M.; Sekiya,
A. Angew. Chem., Int. Ed. 2005, 44, 1128. (b) Gellrich, U.; Meißner, A.;
AUTHOR INFORMATION
Corresponding Author
■
Steffani, A.; Kahny, M.; Drexler, H.-J.; Heller, D.; Plattner, D. A.; Breit,
̈
B. J. Am. Chem. Soc. 2014, 136, 1097.
(17) Mao, J.-G.; Bao, W.-L. Chem. Commun. 2014, 50, 15726.
(18) (a) Beak, P.; Meyers, A. I. Acc. Chem. Res. 1986, 19, 356. (b) Beak,
P.; Basu, A.; Gallagher, D. J.; Park, Y. S.; Thayumanavan, S. Acc. Chem.
Res. 1996, 29, 552. (c) Martin, R.; Buchwald, S. L. Acc. Chem. Res. 2008,
*E-mail: wlbao@zju.edu.cn.
Notes
The authors declare no competing financial interest.
41, 1461. (d) Fernan
Soc. 2004, 126, 12551. (e) Herrero-Gom
Lopez, S.; Benet-Buchholz, J.; Echavarren, A. M. Angew. Chem., Int. Ed.
2006, 45, 5455.
́
dez, I.; Gonzal
́
ez, J.; Lop
́
ez-Ortiz, F. J. Am. Chem.
́
ez, E.; Nieto-Oberhuber, C.;
ACKNOWLEDGMENTS
■
́
Financial support from the Natural Science Foundation of China
(No. 21072168) and the PhD research startup foundation of
Jiangxi University of Science and Technology (No. jxxjbs15009)
is greatly appreciated.
(19) In order to avoid the influence of H/D exchange of CD3OD with
−OCH3 of CH3ONa and CH3OH from the hydrolyzation of CH3ONa
on deuterium-labeling experiments, Cs2CO3 was employed as base to
carry out the reaction mechanism research.
(20) (a) Martins, A.; Mariampillai, B.; Lautens, M. In C-H Activation.;
Yu, J.-Q., Shi, Z., Eds.; Springer: New York, 2010; Vol. 292, pp 1−33
and most pertinent references therein. (b) Shi, F.; Larock, R. C. C−H
Activation. In Topics in Current Chemistry; Yu, J.-Q., Shi, Z., Eds.;
Springer: New York, 2010; Vol. 292, pp 123−164 and most pertinent
references therein. (c) Desai, L. V.; Sanford, M. S. Angew. Chem., Int. Ed.
2007, 46, 5737. (d) Enthaler, S.; Company, A. Chem. Soc. Rev. 2011, 40,
4912. (e) Wu, X.; Fors, B. P.; Buchwald, S. L. Angew. Chem., Int. Ed.
2011, 50, 9943. (f) Shen, C.; Xia, H.; Yan, H.; Chen, X.; Ranjit, S.; Tan,
D.; Lee, R.; Huang, K.-W.; Zhang, P.; Liu, X. Chem. Sci. 2012, 3, 2388.
(g) Mo, D.-L.; Yuan, T.; Ding, C.-H.; Dai, L.-X.; Hou, X.-L. J. Org. Chem.
2013, 78, 11470.
(21) (a) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2.
(b) Amatore, C.; Jutand, A.; Meyer, G.; Mottier, L. Chem. - Eur. J. 1999,
5, 466. (c) Fristrup, P.; Ahlquist, M.; Tanner, D.; Norrby, P.-O. J. Phys.
́
Chem. A 2008, 112, 12862. (d) Camasso, N. M.; Perez-Temprano, M.
H.; Sanford, M. S. J. Am. Chem. Soc. 2014, 136, 12771.
(22) (a) Mattheis, C.; Braunstein, P. J. Organomet. Chem. 2001, 621,
218. (b) Liu, H.; Chen, C.; Wang, L.; Tong, X. Org. Lett. 2011, 13, 5072.
(c) Jiang, X.; Liu, H.; Gu, Z. Asian J. Org. Chem. 2012, 1, 16.
(23) (a) Roberts, J. D.; Lee, C. C.; Saunders, W. H., Jr J. Am. Chem. Soc.
1954, 76, 4501. (b) Li, Y.; Liu, X.; Jiang, H.; Liu, B.; Chen, Z.; Zhou, P.
Angew. Chem., Int. Ed. 2011, 50, 6341. (c) Wu, W.; Jiang, H. Acc. Chem.
Res. 2014, 47, 2483.
(24) (a) Torraca, K. E.; Huang, X.; Parrish, C. A.; Buchwald, S. L. J. Am.
Chem. Soc. 2001, 123, 10770. (b) Guram, A. S.; Bei, X.; Turner, H. W.
Org. Lett. 2003, 5, 2485. (c) Bei, X.; Hagemeyer, A.; Volpe, A.; Saxton,
R.; Turner, H.; Guram, A. S. J. Org. Chem. 2004, 69, 8626.
(d) Vorogushin, A. V.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc.
2005, 127, 8146.
REFERENCES
■
(1) (a) Crowley, M. P.; Inglis, H. S.; Snarey, M.; Thain, E. M. Nature
1961, 191, 281. (b) Hata, Y.; Zimmermann, S.; Quitschau, M.; Kaiser,
M.; Hamburger, M.; Adams, M. J. Agric. Food Chem. 2011, 59 (17),
9172.
(2) (a) Pietruszka, J. Chem. Rev. 2003, 103, 1051. (b) Hiratsuka, T.;
Suzuki, H.; Kariya, R.; Seo, T.; Minami, A.; Oikawa, H. Angew. Chem.,
Int. Ed. 2014, 53, 5423.
(3) (a) Hofmann, K.; Jucker, O.; Miller, W. R.; Young, A. C., Jr.;
Tausig, F. J. Am. Chem. Soc. 1954, 76 (7), 1799.
(4) (a) Chen, J.; Levant, B.; Jiang, C.; Keck, T. M.; Newman, A. H.;
Wang, S. J. Med. Chem. 2014, 57, 4962.
(5) (a) Wiberg, K. B. Acc. Chem. Res. 1996, 29, 229. (b) de Meijere, A.
Chem. Rev. 2003, 103, 931. (c) Fedorynski, M. Chem. Rev. 2003, 103,
̃
1099. (d) Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem.
Rev. 2003, 103, 977. (e) Reissig, H.-U.; Zimmer, R. Chem. Rev. 2003,
103, 1151. (f) Wessjohann, L. A.; Brandt, W.; Thiemann, T. Chem. Rev.
2003, 103, 1625.
(6) (a) Carbocyclic Three-Membered Ring Compounds; de Meijere, A.,
Ed.; Houben-Weyl, Thieme: Stuttgart, 1997. (b) Brandi, A.; Goti, A.
Chem. Rev. 1998, 98, 589. (c) Rubin, M.; Rubina, M.; Gevorgyan, V.
Chem. Rev. 2007, 107, 3117. (d) Shi, M.; Lu, J.-M.; Wei, Y.; Shao, L.-X.
Acc. Chem. Res. 2012, 45, 641. (e) Zhang, D.-H.; Tang, X.-Y.; Shi, M. Acc.
Chem. Res. 2014, 47, 913.
(7) (a) Goudreau, S. R.; Charette, A. B. Angew. Chem., Int. Ed. 2010, 49,
486. (b) Oonishi, Y.; Kitano, Y.; Sato, Y. Angew. Chem., Int. Ed. 2012, 51,
7305. (c) Masutomi, K.; Noguchi, K.; Tanaka, K. J. Am. Chem. Soc. 2014,
136, 7627. (d) Du, W.; Gu, Q.; Li, Z.; Yang, D. J. Am. Chem. Soc. 2015,
137, 1130. (e) Satake, A.; Nakata, T. J. Am. Chem. Soc. 1998, 120, 10391.
(8) (a) Miki, K.; Nishino, F.; Ohe, K.; Uemura, S. J. Am. Chem. Soc.
2002, 124, 5260. (b) Biswas, A.; De Sarkar, S.; Tebben, L.; Studer, A.
Chem. Commun. 2012, 48, 5190. (c) Lindsay, V. N. G.; Fiset, D.; Gritsch,
P. J.; Azzi, S.; Charette, A. B. J. Am. Chem. Soc. 2013, 135, 1463.
(9) (a) Simmons, H. E.; Smith, R. D. J. Am. Chem. Soc. 1958, 80, 5323.
(b) Beaulieu, L.-P. B.; Schneider, J. F.; Charette, A. B. J. Am. Chem. Soc.
2013, 135, 7819.
(10) (a) Xie, H.; Zu, L.; Li, H.; Wang, J.; Wang, W. J. J. Am. Chem. Soc.
2007, 129, 10886. (b) Xuan, Y.; Nie, S.; Dong, L.; Zhang, J.; Yan, M. Org.
Lett. 2009, 11, 1583.
(11) (a) Bruneau, C. Angew. Chem., Int. Ed. 2005, 44, 2328. (b) Miege,
F.; Meyer, C.; Cossy, J. Angew. Chem., Int. Ed. 2011, 50, 5932.
(12) (a) Miura, T.; Sasaki, T.; Harumashi, T.; Murakami, M. J. Am.
Chem. Soc. 2006, 128, 2516. (b) Bigeault, J.; Giordano, L.; Buono, G.
Angew. Chem., Int. Ed. 2005, 44, 4753.
(13) (a) Mao, J.-G.; Bao, W.-L. Org. Lett. 2014, 16, 2646. (b) Mao, J.-
G.; Zhang, S.-Q.; Shi, B.-F.; Bao, W.-L. Chem. Commun. 2014, 50, 3692.
3681
DOI: 10.1021/acs.orglett.5b01603
Org. Lett. 2015, 17, 3678−3681