Highly site-selective direct C-H bond functionalization of phenols with α-aryl-α-diazoacetates and diazooxindoles via gold catalysis

Article abstract of DOI:10.1021/ja503163k

An unprecedented direct C-H bond functionalization of unprotected phenols with α-aryl α-diazoacetates and diazooxindoles was developed. A tris(2,4-di-tert-butylphenyl) phosphite derived gold complex promoted the highly chemoselective and site-selective C-H bond functionalization of phenols and N-acylanilines with gold-carbene generated from the decomposition of diazo compounds, furnishing the corresponding products in moderate to excellent yields at rt. The salient features of this reaction include readily available starting materials, unprecedented C-H functionalization rather than X-H insertion, good substrate scope, mild conditions, high efficiency, and ease in further transformation. To the best of our knowledge, this is the first example of C-H functionalization of unprotected phenols with diazo compounds.

Full text of DOI:10.1021/ja503163k

Communication
pubs.acs.org/JACS
Highly Site-Selective Direct C−H Bond Functionalization of Phenols
with α‑Aryl-α-diazoacetates and Diazooxindoles via Gold Catalysis
Zhunzhun Yu,† Ben Ma,† Mingjin Chen, Hai-Hong Wu, Lu Liu,* and Junliang Zhang*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University,
3663 North Zhongshan Road, Shanghai 200062, China
S
* Supporting Information
compounds is highly challenging because of the competitive
ABSTRACT: An unprecedented direct C−H bond
functionalization of unprotected phenols with α-aryl α-
diazoacetates and diazooxindoles was developed. A
tris(2,4-di-tert-butylphenyl) phosphite derived gold com-
plex promoted the highly chemoselective and site-selective
C−H bond functionalization of phenols and N-acylanilines
with gold-carbene generated from the decomposition of
diazo compounds, furnishing the corresponding products
in moderate to excellent yields at rt. The salient features of
this reaction include readily available starting materials,
unprecedented C−H functionalization rather than X−H
insertion, good substrate scope, mild conditions, high
efficiency, and ease in further transformation. To the best
of our knowledge, this is the first example of C−H
functionalization of unprotected phenols with diazo
compounds.
chemoselective O−H bond insertion in the presence of various
transition-metal catalysts including Rh, Cu, Ru, Fe, and Pd
(Scheme 1a).9 It should be noted that Fu9n and Zhou9o,p have
Scheme 1. Selective Transformations of Phenol with Diazo
Compounds
reported the elegant catalytic asymmetric O−H bond insertion
of phenol with methyl α-aryl α-diazoacetates by the application
of chiral transition metal complexes. Despite the fact that gold
complexes have received a marked increase in interest in organic
synthesis because of the specific carbophilic π-acidic and catalytic
activities,10 the application of gold catalysts to the carbene
transfer reaction has been less explored.8,11 Herein, we wish to
present the first example of a gold-catalyzed intermolecular12
highly site-selective direct C−H bond functionalization of
phenols and N-acylanilines with α-aryl α-diazoacetates under
mild conditions (Scheme 1b). This strategy provides a facile
access to diarylacetates, which are important motifs in natural
products, bioactive and pharmaceutic molecules, and functional
materials (Figure 1).13
henols motifs are widely found in natural products and
Ppharmaceutics as well as common versatile synthons in
organic synthesis due to their wide availability and low price.1
Thus, developing site-selective C−H functionalization of
phenols is highly attractive to the synthetic community. In the
past decade, many indirect methodologies have been developed
via installing the directing group on the hydroxyl to realize ortho/
meta/para functionalization of phenols.2 Maximizing synthetic
efficiency to utilize as much as possible the atoms of reactants is a
very important but challenging task in organic chemistry.3
Therefore, the development of a novel approach to site-selective
direct C−H functionalization of unprotected phenols would be
highly desirable. Ideally, such a strategy requires finishing in one
conveniently operational step and being scalable. In addition,
mild conditions and a low catalyst loading are also important.
Recently, Bedford et al. realized direct ortho C−H arylation of
phenols using a catalytic amount of phosphites as traceless
directing groups.4 Additional ground-breaking work by Larrosa
et al. includes direct meta C−H arylation of unprotected phenols
using CO2 as a traceless relay directing group.5
The initial experiment was performed with methyl α-phenyl-α-
diazoacetate 1a and phenol 2a in the presence of Ph3PAuCl (5
mol %) and AgSbF6 (5 mol %) in dichloromethane (DCM) at rt.
We were pleased to find that the desired para C−H bond
Yet, one of the most effective methods for aromatic C−H
functionalization is the carbene transfer reaction of diazo
compounds in the presence of transition-metal complexes,
with, e.g., rhodium, copper, silver, palladium, etc.6 Yu,7a Rovis,7b
Figure 1. Diarylacetate subunit in natural products and bioactive
molecules.
Per
́
es and co-workers8 have made significant contributions to the
transition-metal-catalyzed direct C−H functionalization of
aromatic compounds involving diazo compounds. However,
the direct C−H functionalization of phenols with diazo
Received: March 29, 2014
Published: April 29, 2014
© 2014 American Chemical Society
6904
dx.doi.org/10.1021/ja503163k | J. Am. Chem. Soc. 2014, 136, 6904−6907

Journal of the American Chemical Society
Communication
functionalization product 3aa could be isolated with a promising
33% yield as a single regioisomer, albeit the O−H insertion
product 4aa was still isolated as the major product in 46% yield
(Table 1, entry 1). Then various types of ligands were screened.
Scheme 2. Scope of Diazo Compounds
a
Table 1. Screening Ligands
b
b
entry
ligand (L)
Ph3P
yield (%) 3aa
yield (%) 4aa
1
2
3
4
5
(32)
39
(46)
49
27
0
(2-biphenyl)Cy2P
(EtO)3P
47
(PhO)3P
(2,4-tBu2C6H3O)3P
82
100 (99)
0
a
The reaction was carried out with 1a (0.4 mmol), 2a (0.6 mmol),
Scheme 3. Scope of Substituted Phenols
catalyst (5 mol %) in solvent (4 mL) at room temperature. The
solution of 1a in 1 mL of CH2Cl2 was introduced into the reaction
mixture by a syringe in 5 min and then being stirred for another 1 min.
b
NMR yield. The numbers in parentheses are isolated yields.
A slightly better result was obtained by adding more electron-rich
phosphine ligand [1,1′-biphenyl]-2-yldicyclohexylphosphine
((2-biphenyl)Cy2P) (Table 1, entry 2). The yield of product
3aa was improved to 47% with 27% 4aa by the use of triethyl
phosphite as the ligand (Table 1, entry 3). Gratifyingly, a
triphenyl phosphite derived gold complex could give the para
C−H functionalization product 3aa in 82% yield (Table 1, entry
4). Tris(2,4-di-tert-butylphenyl) phosphite was then identified to
be optimal in terms of reactivity and selectivity, furnishing 3aa in
99% isolated yield, and no any 4aa and ortho and meta C−H
functionalization product was detectable (Table 1, entry 5,
standard conditions). Other gold catalysts, silver salts, and
solvents gave poorer results, and control experiments showed
that silver salt acts as the halide scavenger rather than a cocatalyst
(for more details, see Table S1, Supporting Information).
With the optimal reaction conditions in hands, we next
investigated the scope of this gold-catalyzed highly site-selective
C−H bond functionalization of phenol 2a by variation of the
component diazo compounds 1. The results are summarized in
Scheme 2. The substituent on the ester group of 1 has no effect
on the yield and selectivity of the reaction. Those α-aryl α-
diazoacetates with both electron-donating and -withdrawing
substituents on the phenyl ring (1c−1f) reacted smoothly with
phenol to give the desired products 3ca−3fa in moderate to
excellent yields (63−99%, Scheme 2). The α-naphth-2-yl α-
diazoacetate 1i and α-thien-2-yl α-diazoacetate 1j also worked,
leading to the corresponding products 3ia and 3ja in 66% and
56% yields, respectively. Besides α-aryl α-diazoacetates, diazo-
oxindoles 1l−o are applicable to the present transformation,
highly selectively furnishing the para C−H bond functionaliza-
tion products 3la−3oa in good to excellent yields (66−93%;
Scheme 2). This transformation provided an alternative strategy
to synthesize 3-aryl oxoindoles with a free hydroxyl group.14 It is
noteworthy that all these reactions are site-specific and chemo-
specific, leading to the para C−H bond functionalization
products as the sole product.
excellent yields of the corresponding C−H functionalization
products 3ab−3bn in a chemo- and regioselective manner. It
should be noted that the reaction of the phenol equipped with an
ortho-allyl substituent gave the para C−H bond functionalization
product 3ag without formation of any product via cyclo-
15
propanation11a
or O−H insertion, indicating that this gold
−g,
catalyst prefers to promote the C−H bond functionalization
rather than the cyclopropanation of an alkene and the O−H
insertion. When meta-methylphenols 2i and meta-methoxyphe-
nol 2j were employed, ortho C−H functionalization products 5ai
and 5aj could be also isolated along with the para C−H
functionalization products 3ai and 3aj, indicating that the methyl
and methyoxy groups could also act as the directing groups. It is
noteworthy that the reaction 3,5-dimethylphenol 2m bearing a
sterically hindered para C−H bond still gave the corresponding
para C−H functionalization product 3am rather than the less
hindered O−H insertion product, showing that the para C−H
functionalization is favored under the reaction conditions. The
structures of 3am and 3bn were confirmed by single-crystal X-ray
crystallography.16
The reactions of various substituted phenols 2b−2n with α-
diazoacetates 1a−b were then examined. As shown in Scheme 3,
the reactions proceeded smoothly, affording moderate to
6905
dx.doi.org/10.1021/ja503163k | J. Am. Chem. Soc. 2014, 136, 6904−6907

Journal of the American Chemical Society
Communication
Furthermore, we became interested in the outcome (O−H
insertion or ortho C−H functionalization) when the para-
substituted phenols were employed. To our delight, the reaction
of 1a and para-mehyl phenol 2p produced the ortho C−H bond
functionalization products 5a in 72% yield. Aryl benzofuranone
6a, a prominent structural motif in natural products (eq 1),17
Scheme 5. Kinetic Isotope Effect
breaking of the C−H bond on phenol was not involved in the
rate-determining step. This result may support that the reaction
proceeds via electrophilic addition of the gold-carbene followed
by rapid 1,2-hydride migration.8,20
It should be noted that this gold-catalyzed site-selective C−H
functionalization of phenols is easy to scale-up. A gram-scale
reaction of 1.46 g of 1a and 1.41 g of 2a was carried out with a
much lower catalyst loading (0.5 mol %), furnishing 1.89 g of the
desired product 3aa in 95% isolated yield (eq 3).
could be efficiently prepared from 5a by TFA-mediated
lactonization. Similarly, 5d, 5h, and benzofuranones 6d and 6h
could be efficiently synthesized following the same procedure;
the relatively lower yield of 5d and 5h resulted from the
competitive dimerization of the diazo compounds under the
standard conditions. The present procedure might be applicable
to late-stage modification of natural products or pharmaceutical
compounds because of its operational convenience and mild
reaction conditions.18 To demonstrate this potential application,
estrone was subjected to the optimized conditions. To our
delight, the catalytic ortho C−H functionalization took place
smoothly to afford 7 in 87% yield, which could undergo a similar
lactonization to give 8 in 97% yield (eq 2).
Most importantly, these products could be viewed as versatile
precursors to synthetic useful building blocks and bioactive
componds (Scheme 6). For example, the bromination of 3aa led
Scheme 6. Synthetic Applications of 3aa
We then wondered whether aniline derivatives are applicable
to the present highly site-selective C−H functionalization, which
is also a challenging issue due to the competitive N−H bond
insertion under the metal catalysis.19 When aniline 9a and N-
methyl aniline 9b were subjected to the reaction under standard
conditions, no reaction occurred. We envisaged that the basic
aniline may inhibit the reactivity of the gold complex via
coordination. Indeed, the reactions proceeded smoothly, when
the basic amine group of aniline was protected by acyl groups
such as acetyl, benzoyl, Boc, etc., furnishing the corresponding
para C−H functionalization products 10c−10g in moderate to
good yields (Scheme 4). The ortho-methyl on N-acetanilide
could slightly improve the yield (10h).
to product 11 in 77% yield.13c Cannabinoid CB1 receptors 13a
and 13b could be efficient prepared from 3aa via successive
hydrolysis and amidation.13b In addition, the hydroxyl is another
versatile group for further transformation. For example, triflate
14 could be easily prepared in 92% yield, which upon metal-
catalyzed coupling reactions furnished compound 15 and useful
arylboron 16 in 86% and 66% yields, respectively.
In summary, we have described the first example of gold-
catalyzed direct C−H functionalization of unprotected phenols
and N-acyl anilines with α-aryl α-diazoacetates and diazoox-
indoles under mild conditions, leading to synthetic useful
diarylacetates with convertible functional groups. This work
would broaden the application of gold catalysts in carbene
transfer reactions. The salient features of this reaction include
readily available starting materials, unprecedented C−H
functionalization rather than X−H insertion and cyclopropana-
tion, good substrate scope, mild conditions, and diverse
convenient transformations of the products.
Although a precise reaction mechanism of the gold-catalyzed
C−H functionalization reaction is unclear, a preliminary
mechanistic study showed that the reaction does not exhibit a
kinetic isotope effect (Scheme 5), thus, indicating that the
Scheme 4. para C−H Bond Functionalization of Anilines
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures and characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Authors
*E-mail: lliu@chem.ecnu.edu.cn.
*E-mail: jlzhang@chem.ecnu.edu.cn.
■
6906
dx.doi.org/10.1021/ja503163k | J. Am. Chem. Soc. 2014, 136, 6904−6907

Journal of the American Chemical Society
Communication
D.-P. Angew. Chem., Int. Ed. 2011, 50, 5952. (l) Osako, T.; Panichakul,
D.; Uozumi, Y. Org. Lett. 2012, 14, 194. (m) Magar, K. B. S.; Lee, Y. R.
Org. Lett. 2013, 15, 4288. For asymmetric version, see: (n) Maier, T. C.;
Fu, G. C. J. Am. Chem. Soc. 2006, 128, 4594. (o) Chen, C.; Zhu, S.-F.;
Liu, B.; Wang, L.-X.; Zhou, Q.-L. J. Am. Chem. Soc. 2007, 129, 12616.
(p) Xie, X.-L.; Zhu, S.-F.; Guo, J.-X.; Cai, Y.; Zhou, Q.-L. Angew. Chem.,
Int. Ed. 2014, 53, 2978.
(10) For selected recent general reviews, see: (a) Gorin, D. J.; Toste, F.
D. Nature 2007, 446, 395. (b) Hashmi, A. S. K. Chem. Rev. 2007, 107,
3180. (c) Arcadi, A. Chem. Rev. 2008, 108, 3266. (d) Li, Z.; Brouwer, C.;
He, C. Chem. Rev. 2008, 108, 3239. (e) Garayalde, D.; Nevado, C. ACS
Catal. 2012, 2, 1462. (f) Boorman, T. C.; Larrosa, I. Chem. Soc. Rev.
Author Contributions
†Z.Y. and B.M. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by the National Natural Science Foundation of
China (21372084, 21373088), Changjiang Scholars and
Innovative Research Team in University (PCSIRT) are greatly
appreciated. We thank Prof. Wenhao Hu, Prof. Shunying Liu,
and Dr. Dong Xing at ECNU for kindly providing the samples of
1d, 1f, and 1h.
2011, 40, 1910. (g) Jimen
2008, 108, 3326.
(11) For selected recent examples, see: (a) Fructos, M. R.; deFremont,
P.; Nolan, S. P.; Díaz-Requejo, M. M.; Perez, P. J. Organometallics 2006,
́
ez-Nunez, E.; Echavarren, A. M. Chem. Rev.
́
̃
́
REFERENCES
■
25, 2237. (b) Zhou, Y.; Trewyn, B. G.; Angelici, R. J.; Woo, L. K. J. Am.
Chem. Soc. 2009, 131, 11734. (c) Briones, J. F.; Davies, H. M. L. J. Am.
Chem. Soc. 2012, 134, 11916. (d) Briones, J. F.; Davies, H. M. L. J. Am.
Chem. Soc. 2013, 135, 13314. (e) Cao, Z.-Y.; Wang, X.; Tan, C.; Zhao,
X.-L.; Zhou, J.; Ding, K. J. Am. Chem. Soc. 2013, 135, 8197. (f) Pagar, V.
V.; Jadhav, A. M.; Liu, R. S. J. Am. Chem. Soc. 2011, 133, 20728.
(12) Only one example of intramolecular C−H functionalization of
phenol with diazoketone was reported, furnishing a mixture of ortho-
and para-substituted isomers or the ortho-substituted isomer as the sole
product; see: Huang, Y.; Zhang, J.; Pettus, T. R. R. Org. Lett. 2005, 7,
5841.
(1) Tyman, J. H. P. Synthetic and Natural Phenols; Elsevier: 1996.
(2) For selected recent examples, for ortho C−H functionalization, see:
(a) Boebel, T. A.; Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 7534.
(b) Zhao, X.; Yeung, C. S.; Dong, V. M. J. Am. Chem. Soc. 2010, 132,
5837. (c) Xiao, B.; Fu, Y.; Xu, J.; Gong, T.-J.; Dai, J.-J.; Yi, J.; Liu, L. J. Am.
Chem. Soc. 2010, 132, 468. (d) Huang, C.; Chattopadhyay, B.;
Gevorgyan, V. J. Am. Chem. Soc. 2011, 133, 12406. (e) Dai, H.-X.; Li,
G.; Zhang, X.-G.; Stepan, A. F.; Yu, J.-Q. J. Am. Chem. Soc. 2013, 135,
7567. (f) Luo, S.; Luo, F.-X.; Zhang, X.-S.; Shi, Z.-J. Angew. Chem., Int.
Ed. 2013, 52, 10598. For meta C−H functionalization, see: (g) Leow,
D.; Li, G.; Mei, T.-S.; Yu, J.-Q. Nature 2012, 486, 518. (h) Wan, L.;
Dastbaravardeh, N.; Li, G.; Yu, J.-Q. J. Am. Chem. Soc. 2013, 135, 18056
and references therein. For para C−H functionalization, see: (i) Ciana,
C.-L.; Phipps, R. J.; Brandt, J. R.; Meyer, F.-M.; Gaunt, M. J. Angew.
Chem., Int. Ed. 2011, 50, 458.
(13) (a) Autore, G.; Caruso, A.; Marzocco, S.; Nicolaus, B.; Palladino,
C.; Pinto, A.; Popolo, A.; Sinicropi, M. S.; Tommonaro, G.; Saturnino,
C. Molecules 2010, 15, 2028. (b) Urbani, P.; Cascio, M. G.; Ramunno,
A.; Bisogno, T.; Saturnino, C.; Marzo, V. D. Bioorg. Med. Chem. 2008, 16,
7510. (c) Zhao, J.; Fan, X.; Wang, S.; Li, S.; Shang, S.; Yang, Y.; Xu, N.;
Lv, Y.; Shi, J. J. Nat. Prod. 2004, 67, 1032. (d) Suzuki, T.; Nakagawa, Y.;
Takano, I.; Yaguchi, K.; Yasuda, K. Environ. Sci. Technol. 2004, 38, 2389.
(e) Cheeseright, T. J.; Melville, J. L.; Gottert, M.; Holm, M.; Laufer, S.;
Lehmann, F.; Luik, S. J. Med. Chem. 2009, 52, 4200.
(3) (a) Trost, B. M. Science 1991, 254, 1471. (b) Sheldon, R. A. Pure
Appl. Chem. 2000, 72, 1233. (c) Anastas, P.; Eghbali, N. Chem. Soc. Rev.
2010, 39, 301.
(4) (a) Bedford, R. B.; Coles, S. J.; Hursthouse, M. B.; Limmert, M. E.
Angew. Chem., Int. Ed. 2003, 42, 112. (b) Bedford, R. B.; Limmert, M. E.
J. Org. Chem. 2003, 68, 8669.
(14) Altman, R. A.; Hyde, A. M.; Huang, X.; Buchwald, S. L. J. Am.
Chem. Soc. 2008, 130, 9613.
(5) Luo, J.; Preciado, S.; Larrosa, I. J. Am. Chem. Soc. 2014, 136, 4109
and references therein.
(15) For reviews on cyclopropanantions with carbene, see: (a) Maas,
G. Chem. Soc. Rev. 2004, 33, 183. (b) Zhang, Z.; Wang, J. Tetrahedron
2008, 64, 6577. (c) Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998, 98, 911.
(d) Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. Rev.
2003, 103, 977. (e) Pellissier, H. Tetrahedron 2008, 64, 7041. (f) Doyle,
M. P. Angew. Chem., Int. Ed. 2009, 48, 850. (g) Obradors, C.; Echavarren,
A. M. Acc. Chem. Res. 2014, 47, 902.
(6) (a) Doyle, M. P.; McKervey, M. A. Modern Catalytic Methods for
Organic Synthesis with Diazo Compounds; Wiley: New York, 1998.
(b) Doyle, M. P.; Duffy, R.; Ratnikov, M.; Zhou, L. Chem. Rev. 2010,
110, 704. (c) Davies, H. M. L.; Lian, Y.-J. Acc. Chem. Res. 2012, 45, 923.
(d) Davies, H. M. L.; Morton, D. Chem. Soc. Rev. 2011, 40, 1857.
́
(e) Díaz-Requejo, M. M.; Perez, P. J. Chem. Rev. 2008, 108, 3379.
(16) CCDC 993363 (3am), 993364 (3bn).
(f) Liu, Z.; Wang, J. J. Org. Chem. 2013, 78, 10024. (g) DeAngelis, A.;
Shurtleff, V. W.; Dmitrenko, O.; Fox, J. M. J. Am. Chem. Soc. 2011, 133,
1650. (h) Rosenfeld, M. J.; Shankar, B. K.; Shechter, H. J. Org. Chem.
1988, 53, 2699. (i) Yang, M.; Webb, T. R.; Livant, P. J. Org. Chem. 2001,
66, 4945. (j) Yadagiri, D.; Anbarasan, P. Org. Lett. 2014, 16, 2510.
(7) For Rh, see: (a) Chan, W.-W.; Lo, S.-F.; Zhou, Z.; Yu, W.-Y. J. Am.
Chem. Soc. 2012, 134, 13565. (b) Hyster, T. K.; Ruhl, K. E.; Rovis, T. J.
Am. Chem. Soc. 2013, 135, 5364.
(17) For the natural product aglalactone with a benzofuranone core,
see: Brader, G.; Vajrodaya, S.; Greger, H.; Bacher, M.; Kalchhauser, H.;
Hofer, O. J. Nat. Prod. 1998, 61, 1482.
(18) (a) Newhouse, T.; Baran, P. S.; Hoffmann, R. W. Chem. Soc. Rev.
2009, 38, 3010. (b) Mcmurray, L.; O’Hara, F.; Gaunt, M. J. Chem. Soc.
Rev. 2011, 40, 1885. (c) Yamaguchi, J.; Yamaguchi, A. D.; Itami, K.
Angew. Chem., Int. Ed. 2012, 51, 8960. (d) Sletten, E. M.; Bertozzi, C. R.
Angew. Chem., Int. Ed. 2019, 48, 6974. (e) Antos, J. M.; McFarland, J. M.;
Iavarone, A. T.; Francis, M. B. J. Am. Chem. Soc. 2009, 131, 6301.
(19) For transition-metal-catalyzed N−H insertion of anilines and N-
substituent anilines with α-aryl-α-diazoacetates, see: (a) Zhu, Y.; Liu, X.;
Dong, S.; Zhou, Y.; Li, W.; Lin, L.; Feng, X. Angew. Chem., Int. Ed. 2014,
53, 1636. (b) Liu, B.; Zhu, S.-F.; Zhang, W.; Chen, C.; Zhou, Q.-L. J. Am.
Chem. Soc. 2007, 129, 5834. (c) Zhu, S.-F.; Xu, B.; Wang, G.-P.; Zhou,
Q.-L. J. Am. Chem. Soc. 2012, 134, 436. (d) Deng, Q.-H.; Xu, H.-W.;
Yuen, A. W.-H.; Xu, Z.-J.; Che, C.-M. Org. Lett. 2008, 10, 1529.
(20) Padwa, A.; Austin, D. J.; Price, A. T.; Semones, M. A.; Doyle, M.
P.; Protopopova, M. N.; Winchester, W. R.; Tarn, A. J. Am. Chem. Soc.
1993, 115, 8669.
(8) For Au, see: (a) Fructos, M. R.; Belderrain, T. R.; de Frem
Scott, N. M.; Nolan, S. P.; Díaz-Requejo, M. M.; Perez, P. J. Angew.
Chem., Int. Ed. 2005, 44, 5284. (b) Rivilla, I.; Gomez-Emeterio, B. P.;
́
ont, P.;
́
̃
Fructos, M. R.; Díaz-Requejo, M. M.; Per
30, 2855.
́
ez, P. J. Organometallics 2011,
(9) For reviews, see: (a) Gillingham, D.; Fei, N. Chem. Soc. Rev. 2013,
42, 4918. (b) Guo, X.; Hu, W. Acc. Chem. Res. 2013, 46, 2427. (c) Zhu,
S.-F.; Zhou, Q.-L. Acc. Chem. Res. 2012, 45, 1365. (d) Miller, D. J.;
Moody, C. J. Tetrahedron 1995, 51, 10811. For selected examples, see:
(e) Yates, P. J. Am. Chem. Soc. 1952, 74, 5376. (f) Zhu, Z.; Espenson, J.
H. J. Am. Chem. Soc. 1996, 118, 9901. (g) Qu, Z.; Shi, W.; Wang, J. J. Org.
Chem. 2004, 69, 217. (h) Zhang, Z.; Liu, Y.; Ling, L.; Li, Y.; Dong, Y.;
Gong, M.; Zhao, X.; Zhang, Y.; Wang, J. J. Am. Chem. Soc. 2011, 133,
4330. (i) Sosa, J. R.; Tudjarian, A. A.; Minehan, T. G. Org. Lett. 2008, 10,
5091. (j) Kilpin, K. J.; Paul, U. S. D.; Lee, A.-L.; Crowley, J. D. Chem.
Commun. 2011, 47, 328. (k) Maurya, R. A.; Park, C. P.; Lee, J. H.; Kim,
6907
dx.doi.org/10.1021/ja503163k | J. Am. Chem. Soc. 2014, 136, 6904−6907