Cyanation of Phenol Derivatives with Aminoacetonitriles by Nickel Catalysis

Article abstract of DOI:10.1021/acs.orglett.6b02265

Generation of useful arylnitrile structures from simple aromatic feedstock chemicals represents a fundamentally important reaction in chemical synthesis. The first nickel-catalyzed cyanation of phenol derivatives with metal-free cyanating agents, aminoacetonitriles, is described. A nickel-based catalytic system consisting of a unique diphosphine ligand such as dcype or dcypt enables the cyanation of versatile phenol derivatives such as aryl carbamates and aryl pivalates. The use of aminoacetonitriles as a cyanating agent leads to an environmentally and easy-to-use method for arylnitrile synthesis.

Full text of DOI:10.1021/acs.orglett.6b02265

Letter
pubs.acs.org/OrgLett
Cyanation of Phenol Derivatives with Aminoacetonitriles by Nickel
Catalysis
Ryosuke Takise,† Kenichiro Itami,*,†,‡ and Junichiro Yamaguchi*,§
†Institute of Transformative Bio-Molecules (WPI-ITbM) and Graduate School of Science, Nagoya University, Chikusa, Nagoya
464-8602, Japan
‡JST, ERATO, Itami Molecular Nanocarbon Project, Nagoya University, Chikusa, Nagoya 464-8602, Japan
§Department of Applied Chemistry, Waseda University, 3-4-1 Ohkubo, Shinjuku, Tokyo 169-8555, Japan
S
* Supporting Information
ABSTRACT: Generation of useful arylnitrile structures from simple
aromatic feedstock chemicals represents a fundamentally important
reaction in chemical synthesis. The first nickel-catalyzed cyanation of
phenol derivatives with metal-free cyanating agents, aminoacetoni-
triles, is described. A nickel-based catalytic system consisting of a
unique diphosphine ligand such as dcype or dcypt enables the cyanation of versatile phenol derivatives such as aryl carbamates
and aryl pivalates. The use of aminoacetonitriles as a cyanating agent leads to an environmentally and easy-to-use method for
arylnitrile synthesis.
Scheme 1. Catalytic Cyanation of Phenol Derivatives with
Aminoacetonitriles
itriles are recognized as one of the most important
Nfunctional groups in chemistry. In particular, arylnitriles
are omnipresent in pharmaceutically relevant molecules and
electronic materials.1 Moreover, the nitrile moiety can serve as a
valuable intermediate that can be readily converted into various
functional groups, such as amines, carbonyls, and heterocycles. In
the past few decades, transition-metal-catalyzed cyanation
reactions of aromatic compounds have greatly progressed.2
Although these reactions are reliable for the synthesis of
arylnitriles, many cyanating agents are metal cyanides, such as
CuCN,3 KCN,4 NaCN,5 Zn(CN)2,6 K4[Fe(CN)6],7 and
TMSCN (Scheme 1, eq 1).8 The risk of utilizing metal cyanides
is the generation of hazardous hydrogen cyanide gas and
stoichiometric amounts of metal-containing waste after the
reaction. Although several practical methods for the synthesis of
arylnitriles with nonmetallic cyanating agents have been
developed,9,10 cyanation reactions employing organic cyanating
agents remain in their infancy in synthetic chemistry.
Meanwhile, we have developed a range of coupling reactions
via inert bond activation using unique nickel catalysts.11−13 For
example, a nickel and 1,2-bis(dicyclohexylphosphino)ethane
(dcype) catalytic system enabled the coupling of 1,3-azoles and
phenol derivatives through C−H and C−O bond activation
(Scheme 1, eq 2).13 Furthermore, a nickel-catalyzed α-arylation
of carbonyl compounds was accomplished with an air-stable
t h i o p h e n e - b a s e d p h o s p h i n e l i g a n d , 3 , 4 - b i s -
(dicyclohexylphosphino)thiophene (dcypt).14 The use of phenol
derivatives instead of aryl halides as the aryl source is beneficial
from both synthetic and environmental points of view. Not only
are phenol derivatives generally inexpensive and readily available,
they also generate non-halogen- and non-sulfur-containing
waste. Furthermore, phenol derivatives can be defined as a
novel chemical feedstock.15,16
Following our successful campaign in nickel-catalyzed C−H/
C−O coupling, we set out to investigate the α-arylation of
acetonitriles with phenol derivatives in order to synthesize α-aryl
acetonitriles. Unfortunately, aminoacetonitriles were not trans-
formed into the desired α-arylated products; however, we
serendipitously discovered that this reaction furnished arylni-
triles, indicating that aminoacetonitriles function as organic
cyanating agents in the catalytic reaction (Scheme 1, eq 3). The
use of aminoacetonitriles as cyanating agents in catalytic
Received: August 1, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b02265
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Organic Letters
Letter
reactions is very rare.17 Herein, we report the nickel-catalyzed
cyanation reaction of phenol derivatives with aminoacetonitriles.
Following the above-mentioned discovery of new aromatic
cyanation process, we investigated the effect of reaction
parameters in the catalytic cyanation reaction of p-biphenyl
carbamate 1A with (dimethylamino)acetonitrile (2a) using
Ni(cod)2 as a nickel source at 150 °C for 18 h (Table 1).
Table 2. Cyanation of Various Aryl Carbamates with an
Aminoacetonitrile by Ni/dcype Catalyst
a
a
Table 1. Screening of the Reaction Conditions
b
entry
ligand
base
solvent
toluene
3A (%)
1
PCy3
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Cs2CO3
CsF
0
0
2
dppf
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
1,4-dioxane
THF
3
BINAP
IPr·HCl
dcype
dcypt
dcype
dcype
dcype
dcype
dcype
dcype
dcype
dcype
dcype
0
4
0
a
b
5
52
25
10
37
33
9
Isolated yield. NiBr2 (10 mol %), Zn (60 mol %), and dcype (20
mol %) were used.
6
7
8
To our delight, the combination of air-stable NiBr2 (5.0 mol %)
and Zn (30 mol %) increased the yield of 3A to 86%.
9
K2CO3
KH2PO4
10
11
12
13
14
15
Next, we examined the substrate scope of various aryl
carbamates in the nickel-catalyzed cyanation reaction with
NiBr2/Zn/dcype/K3PO4 in toluene (Table 2). Biphenyl
carbamates 1A and 1B were well tolerated, and the
corresponding products were obtained in moderate to good
yields (3A and 3B). 2-Naphthyl carbamates also reacted well
with the cyanating agent to give arylnitriles 3C and 3D in good
yields. Since polycyclic aromatic hydrocarbons (PAHs) are
attractive building blocks in materials science, we employed their
carbamates under our reaction conditions. We were delighted to
see that the reactions furnished 3E and 3F in 59% and 56% yields,
respectively. A methyl ester moiety was tolerated, providing the
corresponding products 3G−I in moderate yields. Quinoline
carbamates can be converted into 3J and 3K, albeit in slightly
lower yields.
5
K3PO4
K3PO4
K3PO4
K3PO4
50
29
1
DMF
t-amylOH
6
a
1A (0.40 mmol), 2 (2.0 equiv), Ni(cod)2 (5.0 mol %), ligand
(bidentate: 10 mol %, monodentate: 20 mol %), base (1.5 equiv),
b
c
solvent (1.6 mL), 150 °C and 18 h. GC yield. dcype (10 mol %),
d
K3PO4 (2.0 equiv) and toluene (1.6 mL) were used. Isolated yield.
e
NiBr2 (5.0 mol %), Zn (30 mol %), and dcype (10 mol %) were used.
The scope of aryl pivalates in the nickel-catalyzed cyanation
was also examined (Table 3). In this case, we found that dcypt is
more effective than dcype. Alkyl para-substituted aryl pivalates
reacted well with aminoacetonitrile 2f, providing the desired
products 3L−O in good yields. Aryl pivalates bearing a methoxy
group were well tolerated and afforded the target products (3P−
R) in 87%, 65%, and 70% yields, respectively. Even an electron-
rich aromatic compound, dimethoxy benzonitrile 3S, was
obtained in 81% yield (with increased catalyst loading).
Furthermore, amine and amide groups were also tolerated and
provided the corresponding cyanated products in good yields
(3U and 3 V). Both carbazole and flavone derivatives, which are
often present in naturally occurring molecules, were applicable
under our reaction conditions, affording 3W and 3X in good
yields. Delightfully, we found that even estrone and tyrosine
derivatives underwent the cyanation give the corresponding
products (3Y and 3Z) in moderate to good yields.
Since our catalytic system allowed the cyanation of aryl
carbamates and aryl pivalates, we wondered whether tosylate,
mesylate, triflate, sulfamate, and phosphate would also be
reacting substrates (Table 4). Gratifyingly, all these phenol
derivatives were cyanated in good to excellent yields. To the best
of our knowledge, this is the first nickel-catalyzed cyanation
reaction of a tosylate, sulfamate, or phosphate.
Screening of ligands was conducted in the presence of K3PO4
as a base in toluene. Electron-donating ligands such as PCy3 and
IPr did not promote this transformation (Table 1, entries 1 and
4). Although cyanation with diphosphine ligands did not proceed
at all (Table 1, entries 2 and 3), electron-rich and bulky ligands
such as dcype or dcypt facilitated the cyanation reaction to afford
the desired product 3A in 52% (Table 1, entry 5) and 25% (Table
2, entry 6) yields, respectively. Setting dcype as the optimized
ligand, we next investigated the effect of base and solvent.
Interestingly, K3PO4 (weaker inorganic base) greatly promoted
the reaction compared to Cs2CO3, CsF, K2CO3, and KH2PO4
(Table 1, entries 7−10). The yield was diminished without base
(Table 1, entry 11). Toluene and 1,4-dioxane proved to be an
appropriate solvent for this reaction; a change to THF led to
lower yields of the desired product 3A (Table 1, entries 12 and
13). Polar solvents shut down the reaction (Table 1, entries 14
and 15). Next, we examined cyanating agents by screening
different aminoacetonitriles. Changing the amine substituents
from methyl (2a) to ethyl (2b) gave a slightly lower yield of the
product. Aminoacetonitriles bearing more sterically congested
alkyl groups, such as diisopropyl (2c) and dicyclohexyl (2d), did
not promote the reaction at all. However, morpholinoacetonitrile
2f gave access to the cyanated product 3A in 71% isolated yield.
B
DOI: 10.1021/acs.orglett.6b02265
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Organic Letters
Letter
nitriles 3AA, 3AB, and 3AC in good yields. Even simple
cyclohexenyl nitrile derivative 3AD was also obtained in 76%
yield.
Table 3. Cyanation of Various Aryl Pivalates with an
Aminoacetonitrile by Ni/dcypt Catalysis
a
To demonstrate the synthetic application of this method, we
turned our attention to the synthesis of 5CB,19 which is one of
the best known liquid crystal compounds (Scheme 2). With 4-
Scheme 2. Synthesis of 5CB
bromophenyl dimethylcarbamate 4 as the starting material, we
first performed a Suzuki−Miyaura coupling, obtaining biaryl
compound 5. Subsequently, 5 was subjected to the nickel-
catalyzed cyanation to furnish 5CB in 57% overall yield over two
steps. Thus, the orthogonal reactivity of C−Br (with Pd) and C−
O (with Ni) bonds allowed unconventional yet rapid access to
important class of arylnitrile materials, highlighting the synthetic
utility of the newly discovered cyanation reaction.
a
b
Isolated yield. NiBr2 (10 mol %), Zn (60 mol %), and dcypt (20 mol
%) were used.
Table 4. Cyanation of Various Phenol Derivatives with an
Aminoacetonitrile by Ni Catalysis
a
Although the detailed reaction mechanism has not been
unravelled, a plausible mechanism for this transformation is
depicted in Figure 1. We hypothesize that the catalytic cycle of
a
b
c
NMR yield. dcypt was used. dcype was used.
This cyanation can be applicable to the synthesis of alkenyl
nitriles from enol derivatives (Table 5). To this end, 2,3-
bis(dicyclohexylphosphino)thiophene (L1) provided the high-
est yield of the cyanated product.18 Under the influence of
NiBr2/Zn/L1 catalyst, enol derivatives 1AA, 1AB, and 1AC,
which were readily prepared from α-tetralone derivatives in one
step, were smoothly converted to the corresponding alkenyl
Figure 1. Plausible reaction mechanism.
our Ni-catalyzed cyanation reaction is similar to that of
transition-metal-catalyzed cyanation reactions of aryl halides
with metal cyanides.
Initially, C−O oxidative addition of the phenol derivative to
Ni(0) catalyst A proceeded to afford complex B.13c,14a
Subsequently, anion exchange between −OCOZ (Z = t-Bu,
NMe2) and −CN occurred, providing an aryl-Ni−CN complex C
and an iminium salt.20 Finally, the thus generated C underwent
reductive elimination to provide the arylnitrile product with
simultaneous regeneration of Ni(0) species.
Table 5. Cyanation of Various Enol Derivatives with an
Aminoacetonitrile by Ni/L1 Catalysis
In summary, we have discovered the first nickel-catalyzed
cyanation of phenol derivatives with metal-free, organic
cyanating agents, aminoacetonitriles. Aryl carbamates, pivalates,
tosylates, mesylates, triflates, sulfamates, and phosphates as well
as enol derivatives are all tolerated and furnished the
corresponding cyanated products in good yields. Cyanation of
PAHs and naturally occurring complex molecules was also
C
DOI: 10.1021/acs.orglett.6b02265
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Letter
643. (h) Jia, X. F.; Yang, D. P.; Wang, W. H.; Luo, F.; Cheng, J. J. Org.
Chem. 2009, 74, 9470. (i) Yeung, P. Y.; So, C. M.; Lau, C. P.; Kwong, F.
Y. Angew. Chem., Int. Ed. 2010, 49, 8918.
accomplished. Further investigation of the ligand effect and
mechanistic studies are currently ongoing in our laboratories.
(8) (a) Chatani, N.; Hanafusa, T. J. Org. Chem. 1986, 51, 4714.
(b) Sundermeier, M.; Mutyala, S.; Zapf, A.; Spannenberg, A.; Beller, M.
J. Organomet. Chem. 2003, 684, 50.
ASSOCIATED CONTENT
* Supporting Information
■
S
(9) Kim, J.; Kim, H. J.; Chang, S. Angew. Chem., Int. Ed. 2012, 51,
11948.
(10) (a) Sundermeier, M.; Zapf, A.; Beller, M. Angew. Chem., Int. Ed.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.6b02265.
Detailed experimental procedures and spectral data for all
compounds (PDF)
́
2003, 42, 1661. (b) Schareina, T.; Zapf, A.; Cotte, A.; Gotta, M.; Beller,
M. Adv. Synth. Catal. 2011, 353, 777. (c) Ouchaou, K.; Georgin, D.;
Taran, F. Synlett 2010, 2010, 2083. (d) Jiang, B.; Kan, Y.; Zhang, A.
Tetrahedron 2001, 57, 1581. (e) Luo, F.-H.; Chu, C.-I.; Cheng, C.-H.
Organometallics 1998, 17, 1025. (f) Jiang, Z.; Huang, Q.; Chen, S.; Long,
L.; Zhou, X. Adv. Synth. Catal. 2012, 354, 589. (g) Zhang, Z.; Liebeskind,
L. S. Org. Lett. 2006, 8, 4331. (h) Anbarasan, P.; Neumann, H.; Beller, M.
Angew. Chem., Int. Ed. 2011, 50, 519. (i) Kim, J.; Chang, S. J. Am. Chem.
Soc. 2010, 132, 10272. (j) Pawar, A. B.; Chang, S. Chem. Commun. 2014,
50, 448. (k) Pawar, A. B.; Chang, S. Org. Lett. 2015, 17, 660.
(11) Yamaguchi, J.; Muto, K.; Itami, K. Eur. J. Org. Chem. 2013, 2013,
19.
1H and 13C NMR spectra (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: itami@chem.nagoya-u.ac.jp.
*E-mail: junyamaguchi@waseda.jp.
Notes
The authors declare no competing financial interest.
(12) (a) Canivet, J.; Yamaguchi, J.; Ban, I.; Itami, K. Org. Lett. 2009, 11,
1733. (b) Yamamoto, T.; Muto, K.; Komiyama, M.; Canivet, J.;
Yamaguchi, J.; Itami, K. Chem. - Eur. J. 2011, 17, 10113. (c) Amaike, K.;
Muto, K.; Yamaguchi, J.; Itami, K. J. Am. Chem. Soc. 2012, 134, 13573.
(d) Muto, K.; Yamaguchi, J.; Musaev, D. G.; Itami, K. Nat. Commun.
2015, 6, 7508.
(13) (a) Muto, K.; Yamaguchi, J.; Itami, K. J. Am. Chem. Soc. 2012, 134,
169. (b) Meng, L.; Kamada, Y.; Muto, K.; Yamaguchi, J.; Itami, K. Angew.
Chem., Int. Ed. 2013, 52, 10048. (c) Muto, K.; Yamaguchi, J.; Lei, A.;
Itami, K. J. Am. Chem. Soc. 2013, 135, 16384. (d) Xu, H.; Muto, K.;
Yamaguchi, J.; Zhao, C.; Itami, K.; Musaev, D. G. J. Am. Chem. Soc. 2014,
136, 14834. (e) Muto, K.; Hatakeyama, T.; Yamaguchi, J.; Itami, K.
Chem. Sci. 2015, 6, 6792.
(14) (a) Takise, R.; Muto, K.; Yamaguchi, J.; Itami, K. Angew. Chem.,
Int. Ed. 2014, 53, 6791. (b) Koch, E.; Takise, R.; Studer, A.; Yamaguchi,
J.; Itami, K. Chem. Commun. 2015, 51, 855.
(15) (a) Li, B.-J.; Yu, D.-G.; Sun, C.-L.; Shi, Z.-J. Chem. - Eur. J. 2011,
17, 1728. (b) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2011, 111, 1346.
(c) Kozhushkov, S. I.; Potukuchi, H. K.; Ackermann, L. Catal. Sci.
Technol. 2013, 3, 562. (d) Tobisu, M.; Chatani, N. Acc. Chem. Res. 2015,
48, 1717. (e) Cornella, J.; Zarate, C.; Martin, R. Chem. Soc. Rev. 2014, 43,
8081.
ACKNOWLEDGMENTS
■
This work was supported by the ERATO program from JST
(K.I.), JSPS KAKENHI Grant Nos. JP16H01011 and
JP16H04148 (to J.Y.), and a JSPS research fellowship for
young scientists (to R.T.). We thank Dr. Eva Koch (University of
Munster) for conducting early stage experiments. ITbM is
supported by the World Premier International Research Center
(WPI) Initiative, Japan.
̈
REFERENCES
■
(1) (a) Fleming, F. F.; Wang, Q. Chem. Rev. 2003, 103, 2035.
(b) Fleming, F. F.; Yao, L.; Ravikumar, P. C.; Funk, L.; Shook, B. C. J.
Med. Chem. 2010, 53, 7902.
(2) (a) Ellis, G. P.; Romney-Alexander, T. M. Chem. Rev. 1987, 87, 779.
(b) Anbarasan, P.; Schareina, T.; Beller, M. Chem. Soc. Rev. 2011, 40,
5049.
(3) (a) Sakamoto, T.; Ohsawa, K. J. Chem. Soc., Perkin Trans. 1 1999,
2323. (b) Jia, X. F.; Yang, D. P.; Zhang, S. H.; Cheng, J. Org. Lett. 2009,
11, 4716.
(4) (a) Takagi, K.; Okamoto, T.; Sakakibara, Y.; Oka, A. Chem. Lett.
1973, 471. (b) Sakakibara, Y.; Okuda, F.; Shimobayashi, A.; Kirino, K.;
Sakai, M.; Uchino, N.; Takagi, K. Bull. Chem. Soc. Jpn. 1988, 61, 1985.
(c) Percec, V.; Bae, J.-Y.; Hill, D. H. J. Org. Chem. 1995, 60, 6895.
(d) Anderson, B. A.; Bell, E. C.; Ginah, F. O.; Harn, N. K.; Pagh, L. M.;
Wepsiec, J. P. J. Org. Chem. 1998, 63, 8224. (e) Yang, C.; Williams, J. M.
Org. Lett. 2004, 6, 2837. (f) Cristau, H.-J.; Ouali, A.; Spindler, J.-F.;
Taillefer, M. Chem. - Eur. J. 2005, 11, 2483.
(16) (a) Tobisu, M.; Shimasaki, T.; Chatani, N. Angew. Chem., Int. Ed.
2008, 47, 4866. (b) Guan, B.-T.; Wang, Y.; Li, B.-J.; Yu, D.-G.; Shi, Z.-J. J.
Am. Chem. Soc. 2008, 130, 14468. (c) Quasdorf, K. W.; Tian, X.; Garg,
N. K. J. Am. Chem. Soc. 2008, 130, 14422. (d) Yu, D.-G.; Shi, Z.-J. Angew.
Chem., Int. Ed. 2011, 50, 7097. (e) Quasdorf, K. W.; Antoft-Finch, A.;
Liu, P.; Silberstein, A. L.; Komaromi, A.; Blackburn, T.; Ramgren, S. D.;
Houk, K. N.; Snieckus, V.; Garg, N. K. J. Am. Chem. Soc. 2011, 133, 6352.
(f) Zarate, C.; Martin, R. J. Am. Chem. Soc. 2014, 136, 2236. (g) Correa,
(5) (a) Okano, T.; Iwahara, M.; Kiji, J. Synlett 1998, 1998, 243.
(b) Zanon, J.; Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125,
2890.
́
A.; Leon, T.; Martin, R. J. Am. Chem. Soc. 2014, 136, 1062. (h) Correa,
A.; Martin, R. J. Am. Chem. Soc. 2014, 136, 7253. (i) Cornella, J.; Jackson,
E. P.; Martin, R. Angew. Chem., Int. Ed. 2015, 54, 4075.
(17) Kotani, S.; Sakamoto, M.; Osakama, K.; Nakajima, M. Eur. J. Org.
Chem. 2015, 2015, 6606.
(6) (a) Maligres, P. E.; Waters, M. S.; Fleitz, F.; Askin, D. Tetrahedron
Lett. 1999, 40, 8193. (b) Chidambaram, R. Tetrahedron Lett. 2004, 45,
1441. (c) Jensen, R. S.; Gajare, A. S.; Toyota, K.; Yoshifuji, M.; Ozawa, F.
Tetrahedron Lett. 2005, 46, 8645. (d) Littke, A.; Soumeillant, M.;
Kaltenbach, R. F., III; Cherney, R. J.; Tarby, C. M.; Kiau, S. Org. Lett.
2007, 9, 1711. (e) Martin, M. T.; Liu, B.; Cooley, B. E., Jr.; Eaddy, J. F.
Tetrahedron Lett. 2007, 48, 2555. (f) Buono, F. G.; Chidambaram, R.;
Mueller, R. H.; Waltermire, R. E. Org. Lett. 2008, 10, 5325.
(7) (a) Schareina, T.; Zapf, A.; Beller, M. Chem. Commun. 2004, 1388.
(b) Weissman, S. A.; Zewge, D.; Chen, C. J. Org. Chem. 2005, 70, 1508.
(c) Schareina, T.; Zapf, A.; Beller, M. Tetrahedron Lett. 2005, 46, 2585.
(d) Grossman, O.; Gelman, D. Org. Lett. 2006, 8, 1189. (e) Schareina,
(18) See the Supporting Information for ligand screening in the
cyanation of alkenyl carbamate 1AA.
(19) Gray, G. W.; Harrison, K. J.; Nash, J. A. J. Chem. Soc., Chem.
Commun. 1974, 431.
(20) It was assumed that the effect of K3PO4 is the acceleration of the
anion exchange between complex B and C.
T.; Zapf, A.; Magerlein, W.; Muller, N.; Beller, M. Tetrahedron Lett.
̈
̈
2007, 48, 1087. (f) Mariampillai, B.; Alliot, J.; Li, M.; Lautens, M. J. Am.
Chem. Soc. 2007, 129, 15372. (g) Schareina, T.; Jackstell, R.; Schulz, T.;
Zapf, A.; Cotte, A.; Gotta, M.; Beller, M. Adv. Synth. Catal. 2009, 351,
D
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