Electrochemical Amination of Less-Activated Alkylated Arenes Using Boron-Doped Diamond Anodes

Article abstract of DOI:10.1002/ejoc.201600048

The anodic C-H amination of aromatic compounds is a powerful and versatile method for the synthesis of aniline derivatives. By using boron-doped diamond (BDD) anodes, a method initially described by Yoshida et al. for electron-rich arenes was expanded to less-activated aromatic systems e.g., simple alkylated benzene derivatives. Anodes based on sp³ carbon seem to be the key for the electrochemical amination reaction. The corresponding primary anilines are obtained in good yields. Despite the cationic intermediates of the electrolytic reaction tert-butyl moieties are tolerated.

Full text of DOI:10.1002/ejoc.201600048

DOI: 10.1002/ejoc.201600048
Communication
Electrochemical C–H Amination
Electrochemical Amination of Less-Activated Alkylated Arenes
Using Boron-Doped Diamond Anodes
Sebastian Herold,[a,b] Sabine Möhle,[a] Michael Zirbes,[a] Frank Richter,[c] Hartmut Nefzger,[c]
and Siegfried R. Waldvogel*[a,b]
Abstract: The anodic C–H amination of aromatic compounds simple alkylated benzene derivatives. Anodes based on sp3
is a powerful and versatile method for the synthesis of aniline carbon seem to be the key for the electrochemical amination
derivatives. By using boron-doped diamond (BDD) anodes, a reaction. The corresponding primary anilines are obtained in
method initially described by Yoshida et al. for electron-rich good yields. Despite the cationic intermediates of the electro-
arenes was expanded to less-activated aromatic systems e.g., lytic reaction tert-butyl moieties are tolerated.
Introduction
sources can lead to surplus electricity since generation and de-
mand do not match. The use in discontinuously operated elec-
trochemical processes offers direct valorization and makes this
methodology even more attractive. Therefore, electrosynthetic
conversions can be considered as “green chemistry”.[11]
Recently, Yoshida and co-workers reported a powerful
method for the electrochemical amination of electron-rich
arenes.[12] The key step in this approach is the nucleophilic trap-
ping of the arene radical cation by pyridine resulting in the
formation of positively charged Zincke intermediates 2.[13]
Those intermediates 2 are protected from further anodic degra-
dation because of the strong electron-withdrawing effect of the
positive charge. After the electrolysis, the amine moiety is re-
leased by ring opening of the pyridinium moiety by piperidine.
A broad variety of arenes has been aminated in good to excel-
lent yields of up to 99 % by using carbon felt as the anode
material (Scheme 1). However, the approach is limited to acti-
vated, quite electron-rich substrates e.g., methoxy-substituted
arenes.
Primary aromatic amines are important precursors for the syn-
thesis of pharmaceuticals,[1] dyes,[2] polymers or materials,[3]
and natural products.[4] A typical protocol for the amination of
aromatic compounds is nitration followed by reduction. How-
ever, regioselectivity as well as functional group tolerance is
usually low.[5] State-of-the-art methods for the regioselective,
catalytic construction of aryl C–N bonds are transition-metal or
copper catalyzed (Buchwald–Hartwig, Chan–Lam) aminations of
aryl halides or organometallics.[6] Modern versions of such con-
versions use ammonia as a nitrogen source.[7] However, these
methods require significant loading of toxic and expensive tran-
sition-metal catalysts as well as the prior installation of leaving
groups e.g., halogens or metals. Recently, approaches for
the direct transformation of aromatic carbon–hydrogen into
carbon–nitrogen bonds were established.[8]
Alternatively, photochemical aminations of arenes based on
photoredox catalysis were developed.[9] Unfortunately, this ap-
proach involves the initial conversion of electricity to light and
requires the use of a photo-sensitizer. Therefore, a direct appli-
cation of electric current would be highly desirable.
Electroorganic synthesis has recently experienced significant
attention and a renaissance of electrosynthesis was ob-
served.[10] Electroorganic transformations can avoid reagent
waste because only electrons are shifted for oxidizing or reduc-
ing substrates. Nowadays, the increase of renewable energy re-
Scheme 1. Electrochemical amination reaction of activated arenes.[12]
[a] Institute of Organic Chemistry, Johannes Gutenberg University Mainz
Duesbergweg 10-14, 55128 Mainz, Germany
E-mail: waldvogel@uni-mainz.de
http://www.chemie.uni-mainz.de/OC/AK-Waldvogel/
[b] Graduate School Material Science in Mainz, Johannes Gutenberg
University Mainz
The introduction of the amino moiety occurs ortho or para
to the methoxy group at the most electron-rich position. If the
formation of regioisomers is possible they will be formed. Simi-
larly, N-mesyl-protected imidazole fragments can be installed at
aromatic cores, which provides an elegant access to N-arylimid-
azoles. If benzylic positions are present the use of N-mesyl imid-
azole as the nucleophile leads exclusively to their functionaliza-
tion.[14] Here, we report the electrochemical amination of less-
activated, alkylated arenes.
Staudingerweg 9, 55128 Mainz, Germany
[c] Covestro Deutschland AG
Kaiser-Wilhelm-Allee 60, 51365 Leverkusen, Germany
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201600048.
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Results and Discussion
Initially we envisioned the amination of the benzylic position
of alkyl arenes, e.g. m-xylene by the Yoshida protocol. The initial
challenge was to find suitable electrolysis conditions for such
less-activated substrates. Specific attention was given to the
electrode material, since in previous studies this turned out to
be the key to success.[15] Initially, using a carbon felt anode we
obtained only moderate results and interestingly, no functional-
ization of the benzylic positions of m-xylene (4) was observed
under the applied electrolysis conditions. The only product ob-
tained was 2,4-dimethylaniline (5). However, the results by us-
ing carbon felt were moderate and prompted us to further
study the direct anodic core amination of m-xylene. For this
specific amination at the aromatic core different electrode ma-
terials, e.g. carbon felt, carbon fleece, platinum, glassy carbon,
were investigated (Scheme 2). For carbon fleece and carbon felt
anodes, where the surface area could not be exactly defined,
the current was varied from 6–36 mA (geometric size carbon
felt: 5.0 × 1.0 × 0.5 cm; carbon fleece: 5.0 × 1.0 cm). For planar
platinum and glassy carbon anodes, the current density was
altered in the range 2–12 mA/cm2. Screening experiments were
conducted in divided teflon cells with a porous glass-frit as sep-
arator (for the detailed experimental setup see Supporting In-
formation). This simple but efficient screening method which
operates at ambient conditions has the advantage that many
different electrolysis parameters, e.g. the current density, can
be varied in a highly efficient way.[15b,16]
Figure 1. Electrochemical amination of m-xylene; screening of carbon felt
5.0 × 1.0 × 0.5 cm (red dots) and carbon fleece 5.0 × 1.0 cm (black squares)
at different currents. [a] GC, internal standard: n-octylbenzene.
anode materials investigated, either showed low performance
or exhibited insufficient electrolytic stability, we decided to em-
ploy boron-doped diamond (BDD). This novel and innovative
electrode material has recently attracted a lot of attention in
C–C cross-coupling reactions.[15b,17] The material, based on sp3
carbon usually shows a higher performance at more positive
potentials than other sp2-carbon-based electrodes.[15c,18]
Scheme 2. Electrochemical amination of m-xylene, employed as test substrate
for screening of electrolytic conditions.
One advantage of carbon felt and carbon fleece is the high
surface area. However, reactive intermediates, e.g. radical cati-
ons, need to diffuse from the electrode surface into the bulk
solution for subsequent chemical reactions. Especially for
carbon felt as the anode, mass transport from the electrode
into the bulk is more difficult because reactive intermediates
might get absorbed by the highly porous material. With carbon
fleece as the anode material, only trace amounts of the desired
2,4-dimethylaniline (5) were obtained. In contrast, carbon felt
showed a better performance with a maximum yield of up to
38 % at a current of 30 mA (Figure 1).
Figure 2. Electrochemical amination of m-xylene; screening of BDD (green
triangles), platinum (blue triangles), glassy carbon (red dots), isostatic graph-
ite (black squares) at different current densities. [a] GC, internal standard: n-
octylbenzene.
Indeed, the best results were obtained at commercially avail-
able boron-doped diamond anodes. At all current densities ap-
plied, BDD showed a significantly better performance than plat-
In addition to carbon felt and carbon fleece, glassy carbon inum, glassy carbon, carbon felt, carbon fleece, or isostatic
and platinum with a planar geometry were used as anodes in graphite. The highest isolated yield at BDD anodes was 60 %
this transformation. However, the desired aniline 5 was ob- at a current density of 8 mA/cm2 (Figure 2). Furthermore, we
tained in less than 10 % yield (GC, internal standard) with these investigated the effect of different concentrations (0.1 M–0.6 M)
materials. Mostly, only trace amounts were found (Figure 2). of tetrabutylammonium tetrafluoroborate as the supporting
Furthermore, fouling of the anode was observed for both plati- electrolyte. A high concentration of anions in the electrolyte
num and glassy carbon (see Supporting Information). Isostatic might help to stabilize anodically formed, highly reactive radical
graphite as the anode gave higher yields of up to 14 % at a cationic species. With a yield of 60 %, the best results were
current density of 12 mA/cm2 (Figure 2). However, for isostatic obtained with 0.2
M and 0.3 M electrolyte solutions. Conse-
graphite strong corrosion of the anode was observed. Since the quently, a 0.2
M
tetrabutylammonium tetrafluoroborate solution
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was used as the electrolyte for the following studies (see Sup-
porting Information).
The applied charge was varied in a range of 2 F to 3.2 F. As
optimized electrolysis conditions a charge of 2.5 F was deter-
mined (see Supporting Information).
To gain an insight into the different performances of the
above-investigated electrode materials in the anodic amination
of less-activated aromatic compounds, CV studies were con-
ducted. However, at isostatic graphite no CV data could be ob-
tained due to corrosion of the working electrode. Furthermore,
no CV measurements were possible with carbon fleece and
carbon felt as working electrodes due to the difficulty of con-
tacting those materials. Thus, only for platinum, BDD, and glassy
carbon, CV data which provided a rationale for the different
behavior of the anode could be obtained. Using a platinum
Figure 4. Cyclic voltammograms of 1.0 m
m-xylene + 12.4 m pyridine (blue line); working electrode: glassy carbon;
electrolyte: 0.1 Bu4NBF4/CH3CN; scan rate: 100 mV/s.
M m-xylene (red line) and 1.0 mM
working electrode, m-xylene (1 m
M
) exhibits an oxidation peak
M
at +1.80 V vs. Fc/Fc+ (Figure 3). Upon addition of 12.4 m
M
pyrid-
M
ine (same excess as in screening experiments), the oxidation
peak of m-xylene was no longer observed. Only the oxidation
peak of pyridine (+2.32 V vs. Fc/Fc+) was found (Figure 3).
peak of m-xylene disappears upon addition of pyridine in the
case of platinum and glassy carbon as the working electrode.
However, the CV data match the results obtained in the screen-
ing experiments and provide a highly consistent picture.
Figure 3. Cyclic voltammograms of 1.0 m
m-xylene + 12.4 m pyridine (blue line); working electrode: platinum; electro-
lyte: 0.1 Bu4NBF4/CH3CN; scan rate: 100 mV/s.
M m-xylene (red line) and 1.0 mM
M
M
Figure 5. Cyclic voltammograms of 1.0 m
m-xylene + 12.4 m pyridine (blue line); working electrode: BDD; electrolyte:
0.1 Bu4NBF4/CH3CN; scan rate: 100 mV/s.
M m-xylene (red line) and 1.0 mM
M
Using glassy carbon as the working electrode, an oxidation
peak of 1.71 V vs. Fc/Fc+ is observed (Figure 4). The oxidation
of m-xylene takes place at a potential 90 mV less positive than
those at platinum and BDD. Upon addition of pyridine the oxid-
ation peak of m-xylene is no longer detectable and only the
oxidation peak of pyridine is visible. The oxidation of pyridine
at a glassy carbon working electrode takes place at 2.72 V vs.
Fc/Fc+ (Figure 4). These data and the formation of a thick black
film at both platinum and glassy carbon anodes are in accord-
ance with the fact that 2,4-dimethylaniline (5) is only obtained
in trace amounts.
M
The optimized electrolysis conditions were applied to a
broad range of alkylated arenes. The 1,3-alkyl substitution pat-
tern leads to the corresponding aniline derivatives in good
yields up to 60 %. Isopropyl substituents on the substrate 6 do
not interfere with the amination process and the corresponding
aniline 7 is obtained in 50 % isolated yield (Table 1, entry 2).
Substrates with non-branched alkyl substituents can also be
successfully treated. Tetrahydronaphthalene 12 is preferentially
aminated at the less-hindered position (Table 1, entry 5). Inter-
Boron-doped diamond as the working electrode gives rise estingly, despite the cationic nature of the intermediates even
to an oxidation peak of m-xylene at 1.80 V vs. Fc/Fc+ (Figure 5). tert-butyl groups are compatible with this particular method.
This oxidation peak is still visible upon addition of pyridine, However, functionalization ortho to a tert-butyl moiety is steri-
which is in line with the results mentioned. Interestingly, at BDD cally hindered leading to slightly lower yields (Table 1, entries 6
the oxidation of pyridine can be observed at a more positive and 7). Most remarkably, the amino moiety is installed adjacent
potential (2.64 V vs. Fc/Fc+) than at platinum (Δ E = 320 mV). to a tert-butyl group in a significant amount forming 16
This can be attributed to an over-potential for the oxidation of (Table 1, entry 6). Steric demand from both adjacent positions
pyridine at BDD. So far we cannot explain why the oxidation are even more pronounced in the amination of mesitylene,
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wherein the corresponding aniline 21 is obtained in only 24 % Conclusions
(Table 1, entry 8).
To conclude, boron-doped diamond shows an outstanding per-
formance for the direct electrochemical amination of less-acti-
vated alkylated arenes. The Yoshida method was significantly
expanded and improved. Ongoing studies are focused on the
functionalization of benzylic positions by this method using
sterically more demanding pyridine derivatives, e.g. 2,6-lutidine.
Table 1. Substrate scope of the anodic amination of alkylated arenes using
boron-doped diamond as electrode material.
Experimental Section
Supporting Information (see footnote on the first page of this
article): For experimental details and analytical data see SI.
Acknowledgments
Financial support from Covestro Deutschland AG (Leverkusen,
Germany) is highly appreciated. S. M. thanks the Fonds der
Chemischen Industrie (FCI) for a Kekulé fellowship.
Keywords: Electrochemical oxidation · Amination · Boron-
doped diamond · Synthetic methods · Sustainable chemistry
[1] a) R. Hili, A. K. Yudin, Nat. Chem. Biol. 2006, 2, 284–287; b) A. W. Czarnik,
Acc. Chem. Res. 1996, 29, 112–113.
[2] a) O. Meth-Cone, M. Smith, J. Chem. Soc. Perkin Trans. 1 1994, 5–7; b)
M. M. Sousa, M. J. Melo, A. J. Parola, P. J. T. Morris, H. S. Rzepa, J. S.
Seixas de Melo, Chem. Eur. J. 2008, 14, 8507–8513.
[3] a) P. Novák, K. Müller, K. S. V. Santhanam, O. Haas, Chem. Rev. 1997, 97,
207–282; b) A. G. MacDiarmid, A. J. Epstein, Faraday Discuss. Chem. Soc.
1989, 88, 317–332; c) A. G. MacDiarmid, Synth. Met. 1997, 84, 27–34; d) K.
Weissermel, H.-J. Arpe, Industrial Organic Chemistry, Wiley-VCH, Hoboken,
2008.
[4] a) A. L. Bowie, Jr., C. C. Hughes, D. Trauner, Org. Lett. 2005, 7, 5207–5209;
b) T. Fukuyama, L. Xu, S. Goto, J. Am. Chem. Soc. 1992, 114, 383–385.
[5] a) G. A. Olah, M. Ripudaman, S. C. Narang, Nitration: Methods and Mecha-
nisms, VCH Publishers, New York, 1989; b) R. S. Downing, P. J. Kunkeler,
H. van Bekkum, Catal. Today 1997, 37, 121–136.
[6] a) J. F. Hartwig, Acc. Chem. Res. 1998, 31, 852–860; b) J. P. Wolfe, S. Wa-
gaw, J.-F. Marcoux, S. L. Buchwald, Acc. Chem. Res. 1998, 31, 805–818; c)
P. Y. Lam, G. Vincent, C. G. Clark, S. Deudon, P. K. Jadhav, Tetrahedron Lett.
2001, 42, 3415–3418.
[7] a) Q. Shen, J. F. Hartwig, J. Am. Chem. Soc. 2006, 128, 10028–10029; b)
D. S. Surry, S. L. Buchwald, J. Am. Chem. Soc. 2007, 129, 10354–10355; c)
G. D. Vo, J. F. Hartwig, J. Am. Chem. Soc. 2009, 131, 11049–11061; d) T.
Schulz, C. Torborg, S. Enthaler, B. Schäffner, A. Dumrath, A. Spannenberg,
H. Neumann, A. Börner, M. Beller, Chem. Eur. J. 2009, 15, 4528–4533; e)
F. Lang, D. Zewge, I. N. Houpis, R. Volante, Tetrahedron Lett. 2001, 42,
3251–3254; f) J. Kim, S. Chang, Chem. Commun. 2008, 3052–3054; g) H.
Rao, H. Fu, Y. Jiang, Y. Zhao, Angew. Chem. Int. Ed. 2009, 48, 1114–1116;
Angew. Chem. 2009, 121, 1134–1136.
[8] a) A. A. Kantak, S. Potavathri, R. A. Barham, K. M. Romano, B. DeBoef, J.
Am. Chem. Soc. 2011, 133, 19960–19965; b) F. Collet, R. H. Dodd, P. Dau-
ban, Chem. Commun. 2009, 5061; c) K. Foo, E. Sella, I. Thomé, M. D.
Eastgate, P. S. Baran, J. Am. Chem. Soc. 2014, 136, 5279–5282; d) H. J.
Kim, J. Kim, S. H. Cho, S. Chang, J. Am. Chem. Soc. 2011, 133, 16382–
16385; e) K. Sun, Y. Li, T. Xiong, J. Zhang, Q. Zhang, J. Am. Chem. Soc.
2011, 133, 1694–1697; f) L. D. Tran, J. Roane, O. Daugulis, Angew. Chem.
Int. Ed. 2013, 52, 6043–6046; Angew. Chem. 2013, 125, 6159–6162; g) R.
Shrestha, P. Mukherjee, Y. Tan, Z. C. Litman, J. F. Hartwig, J. Am. Chem.
Soc. 2013, 135, 8480–8483; h) G. B. Boursalian, M.-Y. Ngai, K. N. Hojczyk,
T. Ritter, J. Am. Chem. Soc. 2013, 135, 13278–13281.
[a] Isolated yield. All reactions were carried out using a boron-doped dia-
[9] a) N. A. Romero, K. A. Margrey, N. E. Tay, D. A. Nicewicz, Science 2015,
349, 1326–1330; b) L. J. Allen, P. J. Cabrera, M. Lee, M. S. Sanford, J. Am.
Chem. Soc. 2014, 136, 5607–5610.
mond anode, 0.2
(22 °C).
M Bu4NBF4/CH3CN, 1 mmol substrate at room temperature
Eur. J. Org. Chem. 2016, 1274–1278
www.eurjoc.org
1277
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[10] a) J. B. Sperry, D. L. Wright, Chem. Soc. Rev. 2006, 35, 605–621; b) J.-i.
Yoshida, K. Kataoka, R. Horcajada, A. Nagaki, Chem. Rev. 2008, 108, 2265–
2299; c) H. Lund, J. Electrochem. Soc. 2002, 149, 21–33; d) H. J. Schäfer,
A. J. Bard, M. Stratmann, Organic Electrochemistry, Encyclopedia of Electro-
chemistry, Wiley-VCH, Weinheim, 2004; e) B. R. Rosen, E. W. Werner, A. G.
O'Brien, P. S. Baran, J. Am. Chem. Soc. 2014, 136, 5571–5574; f) S. R.
Waldvogel, B. Janza, Angew. Chem. Int. Ed. 2014, 53, 7122–7123; Angew.
Chem. 2014, 126, 7248–7249; g) M. F. Hartmer, S. R. Waldvogel, Chem.
Commun. 2015, 51, 16346–16348; h) J. Barjau, G. Schnakenburg, S. R.
Waldvogel, Angew. Chem. Int. Ed. 2011, 50, 1415–1419; Angew. Chem.
2011, 123, 1451–1455; i) A. Redden, R. J. Perkins, K. D. Moeller, Angew.
Chem. Int. Ed. 2013, 52, 12865–12868; Angew. Chem. 2013, 125, 13103–
13106; j) L. Li, Y. Jiang, C.-C. Zeng, L.-M. Hu, H.-Y. Tian, C. M. Lam, R. D.
Little, J. Org. Chem. 2015, 80, 11021–11030.
[11] a) E. Steckhan, T. Arns, W. R. Heineman, G. Hilt, D. Hoormann, J. Jörissen,
L. Kröner, B. Lewall, H. Pütter, Chemosphere 2001, 43, 63–73; b) B. A.
Frontana-Uribe, R. D. Little, J. G. Ibanez, A. Palma, R. Vasquez-Medrano,
Green Chem. 2010, 12, 2099–2119; c) H. J. Schäfer, C. R. Chim. 2011, 14,
745–765.
[12] a) T. Morofuji, A. Shimizu, J.-I. Yoshida, J. Am. Chem. Soc. 2013, 135, 5000–
5003; b) S. R. Waldvogel, S. Möhle, Angew. Chem. Int. Ed. 2015, 54, 6398–
6399; Angew. Chem. 2015, 127, 6496–6497.
Chem. Int. Ed. 2014, 53, 5210–5213; Angew. Chem. 2014, 126, 5311–5314;
c) I. M. Malkowsky, U. Griesbach, H. Pütter, S. R. Waldvogel, Eur. J. Org.
Chem. 2006, 4569–4572; d) C. Gütz, M. Bänziger, C. Bucher, T. R. Galvão,
S. R. Waldvogel, Org. Process Res. Dev. 2015, 19, 1428–1433; e) C. Edinger,
J. Kulisch, S. R. Waldvogel, Beilstein J. Org. Chem. 2015, 11, 294–301; f)
C. Edinger, S. R. Waldvogel, Eur. J. Org. Chem. 2014, 5144–5148; g) C.
Edinger, V. Grimaudo, P. Broekmann, S. R. Waldvogel, ChemElectroChem
2014, 1, 1018–1021; h) J. Kulisch, M. Nieger, F. Stecker, A. Fischer, S. R.
Waldvogel, Angew. Chem. Int. Ed. 2011, 50, 5564–5567; Angew. Chem.
2011, 123, 5678–5682.
[16] C. Gütz, B. Klöckner, S. R. Waldvogel, Org. Process Res. Dev. 2016, 20, 26–
32.
[17] a) S. R. Waldvogel, B. Elsler, Electrochim. Acta 2012, 82, 434–443; b) S. R.
Waldvogel, A. Kirste, S. Mentizi in Synthetic Diamond Films – Preparation,
Electrochemistry, Characterization and Applications (Eds.: E. Brillas, C. A.
Martínez-Huitle), Wiley VCH, 2011, pp. 483–510; c) S. R. Waldvogel, S.
Mentizi, A. Kirste, Top. Curr. Chem. 2012, 320, 1–31.
[18] a) T. Kashiwagi, B. Elsler, S. R. Waldvogel, T. Fuchigami, M. Atobe, J. Elec-
trochem. Soc. 2013, 160, G3058–G3061; b) A. Kirste, G. Schnakenburg,
S. R. Waldvogel, Org. Lett. 2011, 13, 3126–3129; c) A. Kirste, G. Schnaken-
burg, F. Stecker, A. Fischer, S. R. Waldvogel, Angew. Chem. Int. Ed. 2010,
49, 971–975; Angew. Chem. 2010, 122, 983–987; d) A. Kirste, B. Elsler, G.
Schnakenburg, S. R. Waldvogel, J. Am. Chem. Soc. 2012, 134, 3571–3576;
e) B. Elsler, D. Schollmeyer, S. R. Waldvogel, Faraday Discuss. 2014, 413–
420.
[13] a) H. Lund, Acta Chem. Scand. 1957, 11, 1323–1330; b) B. Reitstöen, V. D.
Parker, Acta Chem. Scand. 1992, 46, 464–468.
[14] T. Morofuji, A. Shimizu, J.-I. Yoshida, J. Am. Chem. Soc. 2014, 136, 4496–
4499.
[15] a) C. Gütz, M. Selt, M. Bänziger, C. Bucher, C. Römelt, N. Hecken, F. Gallou,
T. R. Galvão, S. R. Waldvogel, Chem. Eur. J. 2015, 21, 13878–13882; b) B.
Elsler, D. Schollmeyer, K. M. Dyballa, R. Franke, S. R. Waldvogel, Angew.
Received: January 14, 2016
Published Online: February 12, 2016
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