Synthesis of Aryl Tri- and Difluoromethyl Thioethers via a C H-Thiocyanation/Fluoroalkylation Cascade

Article abstract of DOI:10.1002/chem.201502914

An AlCl₃-catalyzed C H thiocyanation was discovered and combined with a Langlois-type trifluoromethylation to afford aryl trifluoromethyl thioethers directly from arenes, N-thiocyanatosuccinimide (NTS) and Ruppert-Prakash reagent. An analogous combination with a copper-mediated difluoromethylation gives access to aryl difluoromethyl thioethers. Both processes proceed with exceptional regioselectivity for the most electron-rich, sterically least hindered position of the arene. The sulfur and fluoroalkyl groups originate from different sources, so that the use of expensive, preformed fluoroalkylthiolation reagents is avoided. Perfectly formed: An AlCl₃-catalyzed C H thiocyanation was combined with a Langlois-type trifluoromethylation to afford aryl trifluoromethyl thioethers directly from arenes, N-thiocyanatosuccinimide, and TMS-CF₃ (see scheme). An analogous combination of the thiocyanation with a copper-mediated difluoromethylation gives access to aryl difluoromethyl thioethers. The sulfur and fluoroalkyl groups originate from different sources, so that preformed fluoroalkylthiolation reagents are avoided.

Full text of DOI:10.1002/chem.201502914

DOI: 10.1002/chem.201502914
Communication
&
Synthetic Methods |Hot Paper|
Synthesis of Aryl Tri- and Difluoromethyl Thioethers via a CÀH-
Thiocyanation/Fluoroalkylation Cascade
KØvin Jouvin, Christian Matheis, and Lukas J. Goossen*[a]
Abstract: An AlCl3-catalyzed CÀH thiocyanation was dis-
covered and combined with a Langlois-type trifluorome-
thylation to afford aryl trifluoromethyl thioethers directly
from arenes, N-thiocyanatosuccinimide (NTS) and Rup-
pert–Prakash reagent. An analogous combination with
a copper-mediated difluoromethylation gives access to
aryl difluoromethyl thioethers. Both processes proceed
Figure 1. Biologically active trifluoromethyl thioethers.
with exceptional regioselectivity for the most electron-
rich, sterically least hindered position of the arene. The
sulfur and fluoroalkyl groups originate from different sour-
sition metal catalysts, for example, Ni,[10] Cu[11] or Pd com-
ces, so that the use of expensive, preformed fluoroalkyl-
plexes.[12] The seminal report by Shen et al. on the trifluorome-
thiolation reagents is avoided.
thylthiolation of electron-rich arenes with N-trifluoromethyl-
thiosaccharin[13] has triggered substantial efforts to synthesize
aryl trifluoromethyl thioethers by electrophilic CÀH functionali-
zation.[14] However, the drawback of this approach is the high
Presently, 30–40% of marketed agrochemicals and 25% of
pharmaceuticals contain fluorine atoms.[1] As a result, the intro-
duction of fluorine residues into organic molecules is a highly
topical area. In drug discovery, so called “fluorine scans”, that
is, systematic derivatizations of lead structures by replacing
alkyl, hydroxy-, amino-, or thio-substituents with their bioiso-
cost of the reagents, which are synthesized from expensive AgI
fluoride or toxic and corrosive CF3SCl gas (Figure 2).[11a,e,13,15]
[4]
steric fluorinated groups, for example, CF3,[2] CF2H,[3] SCF3 or
OCF3,[5] are routinely carried out. This has created a growing
demand for technologies for the late-stage introduction of
such moieties into functionalized molecules. Powerful methods
for the introduction of CF3 groups have emerged within only
a few years.[6]
Figure 2. Examples of electrophilic trifluoromethylthiolation reagents.
Lately the focus has somewhat shifted towards SCF3
groups,[7] which induce an even higher lipophilicity and mem-
brane permeability into bioactive compounds (Hansch con-
stants 1.44 for SCF3 vs. 0.88 for CF3).[8] Several bioactive com-
pounds such as Tiflorex, Toltrazuril and a Losartan analogue
contain SCF3 groups as a key functionality (Figure 1).
A potential alternative to introducing SCF3 as a whole from
a preformed reagent is its stepwise assembly at the target mol-
ecule. This can be achieved in a straightforward fashion by first
introducing an SCN group and then replacing the CN group
by the CF3 group though a Langlois-type nucleophilic substitu-
tion.[16]
Traditional approaches for the introduction of SCF3 group
are based on halogen exchange from aryl trichloromethyl thio-
ethers using HF or SbF3, the so-called Swarts reaction,[9] which
is inexpensive but has a rather low functional group tolerance.
Modern trifluoromethylthiolation reactions suitable for late-
stage derivatizations are based on preformed nucleophilic,
electrophilic or radical SCF3 reagents in combination with tran-
We have recently shown that nucleophilic thiocyanations of
alkyl halides or Sandmeyer thiocyanations of aryldiazonium
salts can be combined with Langlois-type exchange reactions
into convenient one-pot procedures.[17] These allow the con-
version of various electrophiles into di- and trifluoromethylth-
iolated compounds using simple thiocyanate salts in combina-
tion with inexpensive fluoroalkylation reagents. We envisioned
that a similar stepwise assembly might enable inexpensive and
straightforward di- and trifluoroalkylthiolations of aromatic CÀ
H bonds (Scheme 1). If electrophilic CÀH thiocyanations based
on easily accessible, stable reagents could be combined with
an exchange of CN for CF3 or CF2H, di- and trifluoromethyl
thioethers would become accessible from simple arenes rather
than prefunctionalized substrates or expensive reagents.
[a] Dr. K. Jouvin, C. Matheis, Prof. Dr. L. J. Goossen
FB Chemie-Organische Chemie, Technische Universität Kaiserslautern
Erwin-Schrçdinger-Strasse Geb. 54, 67663 Kaiserslautern (Germany)
E-mail: goossen@chemie.uni-kl.de
Homepage: http://www.chemie.uni-kl.de/goossen
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502914.
Chem. Eur. J. 2015, 21, 14324 – 14327
14324
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
can alternatively be performed with 1% AuCl3 as a catalyst in
dichloroethane,[22] and that these conditions permit the subse-
quent trifluoromethylation to give 4 in moderate yields along
with residual thiocyanate (entry 3). A decisive step-up in the
yield of this two-step process was achieved by switching to
MeCN as the solvent (entries 4–7). Further studies revealed
that the transformation was catalyzed not only by gold but
also by inexpensive Lewis acids, and AlCl3 in particular
(entry 8). After increasing the catalyst loading to 10 mol%, full
conversion was reached after 12 h at RT (entry 9). ZrCl4 dis-
played similarly high activity, other Lewis acids less so (en-
tries 10–12). Without Lewis acid, no conversion was observed
(entry 14). The regioselectivity is remarkable. Whereas Friedel–
Crafts chlorination of anisole usually provides a para/ortho
ratio of 79:21,[23] the thiocyanation gives the para-substituted
product exclusively.
Scheme 1. Electrophilic trifluoromethylthiolations via a CÀH thiocyanation/
fluoroalkylation cascade.
We considered N-thiocyanatosuccinimide (NTS) to be the
electrophilic reagent of choice, because it is readily available
from N-bromosuccinimide (NBS) and NaSCN.[18] So far, it has
been used only in the thiocyanation of thiols[18] and N-acyl
imides.[19] Still et al. have shown that Friedel–Crafts thiocyana-
tion of electron-rich compounds is possible with NTS formed
in situ in MeOH or AcOH.[20] Unfortunately, these conditions are
incompatible with common fluoroalkylation reagents.
Because the activity of the Friedel–Crafts catalysts is dimin-
ished by Cs2CO3, TBAF or other TMS-CF3 activators but the
AlCl3 catalyst does not affect the trifluoromethylation, the pro-
cess is best performed stepwise in one pot. First, the arene is
allowed to react at RT for 12 h with one equivalent of NTS (2)
in the presence of 10% AlCl3 in MeCN. TMS-CF3 and Cs2CO3 are
then added, and the reaction is stirred for another 2 h
(entry 13).
To identify conditions that promote both the CÀH thiocyana-
tion and the CN/CF3 exchange, we systematically investigated
catalysts, solvents and temperatures for the one-pot reaction
of anisole (1) with NTS (2) and TMS-CF3 (Table 1).
When subjecting 1 and 2 to the conditions reported by Still
et al. (AcOH, 608C) the aryl thiocyanate was formed in high
yields, but subsequent addition of TMS-CF3 and Cs2CO3 did not
afford the desired trifluoromethyl thioether 4 (entry 1).[21] Fur-
ther studies confirmed that protic solvents and Brønsted acids
are incompatible with the trifluoromethylation step (entries 1
and 2). However, we discovered that the CÀH thiocyanation
Next, we investigated the scope of the trifluoromethylthiola-
tion, extending the trifluoromethylation time to 16 h to ensure
full conversion even of less reactive substrates (Table 2). Mayr
has introduced the nucleophilicity parameter N to classify
arenes with regard to their reactivity with electrophiles.[24] We
determined that arenes with an N above a threshold of À2.5
are suitable for the CÀH thiocyanation step. Thus, benzothio-
phene (N=À2.5) and fluorene (N=À2.9) gave reasonable
yields, whereas o-xylene (N=À3.7) or toluene (N=À4.2) did
not react. Various electron-rich arenes and heteroarenes with
N>À2.5 were converted to the aryl trifluoromethyl thioethers
in high yields. Functionalities including alkyloxy, hydroxy, ketal
and amino groups are well tolerated. Sterically demanding
substrates, unprotected phenols, indoles and carbazoles, and
even a pyridine were smoothly converted. Aniline gave a sur-
prisingly low yield, although the thiocyanation proceeded well.
In contrast, both reaction steps were effective for N-methyl ani-
line. Bromo- and iodo-substituents remain intact, which opens
up opportunities for further derivatization.
Table 1. Optimization of the reaction conditions.[a]
Entry Solvent Catalyst
T, t
Conv. 1 [%] Yield 4 [%]
1
2
3
4
5
6
7
8
AcOH
MeOH
DCE
dioxane 1% AuCl3
DMF
–
–
608C, 3 d
608C, 3 d
258C, 3 d
258C, 3 d
258C, 3 d
258C, 3 d
258C, 3 d
258C, 1 d
80
0
100
0
0
0
0
0
48
0
0
0
94
86
99
98
78
54
99
0
1% AuCl3
1% AuCl3
1% AuCl3
1% AuCl3
1% AlCl3
10% AlCl3
10% ZrCl4
10% FeCl3
10% BF3·Et2O 258C, 12 h
10% AlCl3
–
In all reactions, monothiocyanation was exclusively ob-
served, which is understandable because the thiocyanate sub-
stituent reduces the nucleophilicity of arenes (Hammett con-
stants for SCN: sm =0.51, sp =0.52).[25] Only a single regioiso-
mer was formed for all substrates. This degree of selectivity is
exceptional for electrophilic aromatic substitutions, and is
linked to the strong electrophilicity of the SCN moiety.[26]
The scalability of the reaction was demonstrated by the
high-yielding synthesis of 4 on a gram scale. The same strategy
was successfully applied also to the synthesis of difluoromethyl
thioethers, which are hard to access by other means.[17a,27]
Mechanistically, the CN/CF2H exchange is more complex, since
this sensitive nucleophile can be transferred only with a stabiliz-
ing copper mediator that requires DMF to be active.[17a,28] After
THF
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
100
90
9
258C, 12 h 100
258C, 12 h 100
258C, 12 h
10
11
12
13[b]
14
95
80
258C, 12 h 100
258C, 12 h
0
[a] Reaction conditions: 0.5 mmol of anisole (1), the catalyst, and
0.5 mmol of NTS (2) in 1 mL of solvent were stirred at given temperature
for the given amount of time. Then, 1.0 mmol of Cs2CO3 and 1.0 mmol of
TMS-CF3 were added and the reaction mixture was stirred at RT for 12 h.
Conversion of 1 was determined by GC, the yield of 4 by 19F NMR spec-
troscopy using 1 equivalent of trifluoroethanol as internal standard;
[b] 2 h for the Langlois exchange.
Chem. Eur. J. 2015, 21, 14324 – 14327
www.chemeurj.org
14325
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Table 2. Trifluoromethylthiolation of electron-rich arenes.[a]
Table 3. Difluoromethylthiolation of electron-rich arenes.[a]
[a] 1.0 mmol NTS, 0.1 mmol of AlCl3, 2 mL MeCN, 1.0 mmol of arene, RT,
12 h. Then, MeCN is exchanged for 2 mL of DMF; 1.0 mmol of CuSCN,
4.0 mmol of CsF, 2.0 mmol of TMS-CF2H, RT, overnight. Isolated yields.
Table 3. These include ethers, phenols, anilines, pyridine and
indole derivatives.
In conclusion, one-pot, two-step CÀH thiocyanation/fluoroal-
kylation processes were developed that open up convenient
entries to di- and trifluoromethyl thioethers starting from elec-
tron-rich arenes, an inexpensive thiocyanate source and TMS-
CF3 or TMS-CF2H. The CÀH functionalization proceeds exclu-
sively at the most electron-rich, sterically least hindered posi-
tion of the arene.
Experimental Section
Standard procedure for the synthesis of trifluoromethylthio
ethers
An oven-dried 20 mL crimp-cap vessel with stirrer bar was charged
with NTS (156 mg, 1.00 mmol), AlCl3 (13.3 mg, 0.10 mmol), the
arene (1.00 mmol) and MeCN (2 mL). After stirring at the given re-
action temperature for 12 h, Cs2CO3 (652 mg, 2.00 mmol) and TMS-
CF3 (287 mg, 2.00 mmol) was added and the reaction mixture was
stirred at RT for 16 h. The resulting mixture was diluted with dieth-
yl ether (20 mL). The organic solution was washed with water (2”
10 mL) and brine (10 mL). The organic layer was dried over MgSO4,
filtered and concentrated (700 mbar, 408C). The residue was puri-
fied by flash chromatography (SiO2, pentane/diethyl ether gradi-
ent), yielding the aryl trifluoromethyl thioethers. The yields of par-
ticularly volatile compounds were determined by 19F NMR spectros-
copy, and their identity by mass spectroscopy.
[a] 1.0 mmol NTS, 0.1 mmol of AlCl3, 2 mL MeCN, 1.0 mmol of arene, RT,
12 h. Then, 2.0 mmol of Cs2CO3, 2.0 mmol of TMS-CF3, RT, overnight. Iso-
lated yields. [b] The thiocyanation step was performed at 608C. [c] Yield
determinate by 19F NMR spectroscopy using 1 equivalent of trifluoroetha-
nol as standard.
intricate tuning of all reaction parameters, we obtained an effi-
cient difluoromethylthiolation protocol (see the Supporting In-
formation for details), using anisole as the model substrate.
The Friedel–Crafts thiocyanation step requires a maximum of
12 h at RT in the presence of NTS (2) and 10 mol% of AlCl3.
For the subsequent difluoromethylation, acetonitrile was ex-
changed for DMF, followed by addition of copper thiocyanate,
excess cesium fluoride and TMS-CF2H.
Acknowledgements
We thank Christian Rank and Victoria Wagner for technical as-
sistance and Nanokat for financial support.
Keywords: electrophilic
substitution
·
fluorine
·
The scope of the difluoromethylthiolation is similar to the
trifluoromethylthiolation but the yields are somewhat lower
throughout, as demonstrated by the selected examples in
fluoroalkylthiolation · sulfur · synthetic methods
[1] a) Fluorine in Medicinal Chemistry and Chemical Biology (Eds.: I. Ojima),
Wiley, Hoboken, 2009; b) J. Wang, M. Sµnchez-Roselló, J. L. AceÇa, C. del
Chem. Eur. J. 2015, 21, 14324 – 14327
www.chemeurj.org
14326
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Pozo, A. E. Sorochinsky, S. Fustero, V. A. Soloshonok, H. Liu, Chem. Rev.
2014, 114, 2432–2506.
[13] C. Xu, B. Ma, Q. Shen, Angew. Chem. Int. Ed. 2014, 53, 9316–9320;
Angew. Chem. 2014, 126, 9470–9474.
[2] a) O. A. Tomashenko, V. V. Grushin, Chem. Rev. 2011, 111, 4475–4521;
b) T. Furuya, A. S. Kamlet, T. Ritter, Nature 2011, 473, 470–477; c) X.-F.
Wu, H. Neumann, M. Beller, Chem. Asian J. 2012, 7, 1744–1754; d) T.
Liu, Q. Shen, Eur. J. Org. Chem. 2012, 6679–6687; e) T. Liang, C. N. Neu-
mann, T. Ritter, Angew. Chem. Int. Ed. 2013, 52, 8214–8264; Angew.
Chem. 2013, 125, 8372–8423; f) X. Liu, C. Xu, M. Wang, Q. Liu, Chem.
Rev. 2015, 115, 683–730.
[3] a) C. Ni, L. Zhu, J. Hu, Acta Chim. Sinica 2015, 73, 90–115; b) M.-C. Bel-
homme, T. Besset, T. Poisson, X. Pannecoucke, Chem. Eur. J. DOI:
10.1002/chem.201501475; c) P. Xua, S. Guoa, L. Wanga, P. Tang, Synlett
2015, 26, 36–39.
[14] a) Q. Wang, Z. Qi, F. Xie, X. Li, Adv. Synth. Catal. 2015, 357, 355–360;
b) R. Honeker, J. B. Ernst, F. Glorius, Chem. Eur. J. 2015, 21, 8047–8051;
c) M. Jereb, K. Gosak, Org. Biomol. Chem. 2015, 13, 3103–3115.
[15] a) T. Bootwicha, X. Liu, R. Pluta, I. Atodiresei, M. Rueping, Angew. Chem.
Int. Ed. 2013, 52, 12856–12859; Angew. Chem. 2013, 125, 13093–13097;
b) X. Wang, T. Yang, X. Cheng, Q. Shen, Angew. Chem. Int. Ed. 2013, 52,
12860–12864; Angew. Chem. 2013, 125, 13098–13102; c) X.-L. Zhu, J.-
H. Xu, D.-J. Cheng, L.-J. Zhao, X.-Y. Liu, B. Tan, Org. Lett. 2014, 16, 2192–
2195; d) M. Rueping, X. Liu, T. Bootwicha, R. Pluta, C. Merkens, Chem.
Commun. 2014, 50, 2508–2511; e) Y.-D. Yang, A. Azuma, E. Tokunaga, M.
Yamasaki, M. Shiro, N. Shibata, J. Am. Chem. Soc. 2013, 135, 8782–8785.
[16] a) T. Billard, S. Large, B. R. Langlois, Tetrahedron Lett. 1997, 38, 65–68;
b) C. Wakselman, M. Tordeux, J.-L. Clavel, B. Langlois, J. Chem. Soc.
Chem. Commun. 1991, 993–994; c) G. Blond, T. Billard, B. R. Langlois,
Tetrahedron Lett. 2001, 42, 2473–2475; d) C. Pooput, M. Medebielle,
W. R. Dolbier, Org. Lett. 2004, 6, 301–303; e) C. Pooput, W. R. Dolbier, M.
MØdebielle, J. Org. Chem. 2006, 71, 3564–3568; f) K. Yamaguchi, K. Sa-
kagami, Y. Miyamoto, X. Jin, N. Mizuno, Org. Biomol. Chem. 2014, 12,
9200–9206.
[17] a) B. Bayarmagnai, C. Matheis, K. Jouvin, L. J. Goossen, Angew. Chem. Int.
Ed. 2015, 54, 5753–5756; Angew. Chem. 2015, 127, 5845–5848; b) B.
Bayarmagnai, C. Matheis, E. Risto, L. J. Goossen, Adv. Synth. Catal. 2014,
356, 2343–2348; c) C. Matheis, M. Wang, T. Krause, L. Goossen, Synlett
2015, 1628–1632.
[18] M. T. Ashby, H. Aneetha, J. Am. Chem. Soc. 2004, 126, 10216–10217.
[19] J. R. Falck, S. Gao, R. N. Prasad, S. R. Koduru, Bioorg. Med. Chem. Lett.
2008, 18, 1768–1771.
[4] F. Toulgoat, S. Alazet, T. Billard, Eur. J. Org. Chem. 2014, 2415–2428.
[5] a) G. L. Trainor, J. Carbohydr. Chem. 1985, 4, 545–563; b) K. N. Hojczyk,
P. Feng, C. Zhan, M.-Y. Ngai, Angew. Chem. Int. Ed. 2014, 53, 14559–
14563; Angew. Chem. 2014, 126, 14787–14791.
[6] a) G. K. S. Prakash, P. V. Jog, P. T. D. Batamack, G. A. Olah, Science 2012,
338, 1324–1327; b) P. Novµk, A. Lishchynskyi, V. V. Grushin, Angew.
Chem. Int. Ed. 2012, 51, 7767–7770; Angew. Chem. 2012, 124, 7887–
7890; c) E. J. Cho, T. D. Senecal, T. Kinzel, Y. Zhang, D. A. Watson, S. L.
Buchwald, Science 2010, 328, 1679–1681; d) H. Morimoto, T. Tsubogo,
N. D. Litvinas, J. F. Hartwig, Angew. Chem. Int. Ed. 2011, 50, 3793–3798;
Angew. Chem. 2011, 123, 3877–3882; e) N. D. Litvinas, P. S. Fier, J. F.
Hartwig, Angew. Chem. Int. Ed. 2012, 51, 536–539; Angew. Chem. 2012,
124, 551–554; f) G. G. Dubinina, H. Furutachi, D. A. Vicic, J. Am. Chem.
Soc. 2008, 130, 8600–8601; g) T. Liu, X. Shao, Y. Wu, Q. Shen, Angew.
Chem. Int. Ed. 2012, 51, 540–543; Angew. Chem. 2012, 124, 555–558;
h) L. Chu, F.-L. Qing, Org. Lett. 2010, 12, 5060–5063; i) B. A. Khan, A. E.
Buba, L. J. Gooßen, Chem. Eur. J. 2012, 18, 1577–1581; j) G. Danoun, B.
Bayarmagnai, M. F. Grünberg, L. J. Gooßen, Angew. Chem. Int. Ed. 2013,
52, 7972–7975; Angew. Chem. 2013, 125, 8130–8133; k) M. Oishi, H.
Kondo, H. Amii, Chem. Commun. 2009, 1909–1911.
[20] a) F. D. Toste, V. D. Stefano, I. W. J. Still, Synth. Commun. 1995, 25, 1277–
1286; b) F. D. Toste, I. W. J. Still, J. Am. Chem. Soc. 1995, 117, 7261–7262.
[21] G. Danoun, B. Bayarmagnai, M. F. Gruenberg, L. J. Goossen, Chem. Sci.
2014, 5, 1312–1316.
[7] X.-H. Xu, K. Matsuzaki, N. Shibata, Chem. Rev. 2015, 115, 731–764.
[8] C. Hansch, A. Leo, S. H. Unger, K. H. Kim, D. Nikaitani, E. J. Lien, J. Med.
Chem. 1973, 16, 1207–1216.
[22] For an analog bromination, see: F. Mo, J. M. Yan, D. Qiu, F. Li, Y. Zhang,
J. Wang, Angew. Chem. Int. Ed. 2010, 49, 2028–2032; Angew. Chem.
2010, 122, 2072–2076.
[9] a) E. A. Nodiff, S. Lipschutz, P. N. Craig, M. Gordon, J. Org. Chem. 1960,
25, 60–65; b) A. E. Feiring, J. Org. Chem. 1979, 44, 2907–2910; c) V. N.
Boiko, Beilstein J. Org. Chem. 2010, 6, 880–921.
[10] a) C.-P. Zhang, D. A. Vicic, J. Am. Chem. Soc. 2012, 134, 183–185; b) G.
Yin, I. Kalvet, U. Englert, F. Schoenebeck, J. Am. Chem. Soc. 2015, 137,
4164–4172.
[23] B. Jones, E. N. Richardson, J. Chem. Soc. 1956, 3939–3941.
[24] M. F. Gotta, H. Mayr, J. Org. Chem. 1998, 63, 9769–9775.
[25] C. Hansch, A. Leo, R. W. Taft, Chem. Rev. 1991, 91, 165–195.
[26] a) H. C. Brown, C. W. McGary, J. Am. Chem. Soc. 1955, 77, 2300–2306;
b) H. C. Brown, L. M. Stock, J. Am. Chem. Soc. 1957, 79, 5175–5179;
c) H. C. Brown, M. Dubeck, J. Am. Chem. Soc. 1960, 82, 1939–1941;
d) L. M. Stock, H. C. Brown, J. Am. Chem. Soc. 1960, 82, 1942–1947.
[27] a) J. Hine, J. J. Porter, J. Am. Chem. Soc. 1957, 79, 5493–5496; b) B. R.
Langlois, J. Fluorine Chem. 1988, 41, 247–261; c) L. Li, F. Wang, C. Ni, J.
Hu, Angew. Chem. Int. Ed. 2013, 52, 12390–12394; Angew. Chem. 2013,
125, 12616–12620; d) C. S. Thomoson, W. R. Dolbier, J. Org. Chem. 2013,
78, 8904–8908; e) J. Wu, Y. Gu, X. Leng, Q. Shen, Angew. Chem. Int. Ed.
2015, 54, 7648–7652; Angew. Chem. 2015, 127, 7758–7762; f) D. Zhu, Y.
Gu, L. Lu, Q. Shen, J. Am. Chem. Soc. 2015, DOI 10.1021/jacs.5b03170.
[28] a) G. K. S. Prakash, S. K. Ganesh, J.-P. Jones, A. Kulkarni, K. Masood, J. K.
Swabeck, G. A. Olah, Angew. Chem. Int. Ed. 2012, 51, 12090–12094;
Angew. Chem. 2012, 124, 12256–12260; b) C. Matheis, K. Jouvin, L. J.
Goossen, Org. Lett. 2014, 16, 5984–5987.
[11] a) X. Shao, X. Wang, T. Yang, L. Lu, Q. Shen, Angew. Chem. Int. Ed. 2013,
52, 3457–3460; Angew. Chem. 2013, 125, 3541–3544; b) Z. Weng, W.
He, C. Chen, R. Lee, D. Tan, Z. Lai, D. Kong, Y. Yuan, K.-W. Huang, Angew.
Chem. Int. Ed. 2013, 52, 1548–1552; Angew. Chem. 2013, 125, 1588–
1592; c) C. Chen, Y. Xie, L. Chu, R.-W. Wang, X. Zhang, F.-L. Qing, Angew.
Chem. Int. Ed. 2012, 51, 2492–2495; Angew. Chem. 2012, 124, 2542–
2545; d) L. D. Tran, I. Popov, O. Daugulis, J. Am. Chem. Soc. 2012, 134,
18237–18240; e) R. Pluta, P. Nikolaienko, M. Rueping, Angew. Chem. Int.
Ed. 2014, 53, 1650–1653; Angew. Chem. 2014, 126, 1676–1679; f) C.-P.
Zhang, D. A. Vicic, Chem. Asian J. 2012, 7, 1756–1758; g) T. Liu, Q. Shen,
Org. Lett. 2011, 13, 2342–2345.
[12] a) G. Teverovskiy, D. S. Surry, S. L. Buchwald, Angew. Chem. Int. Ed. 2011,
50, 7312–7314; Angew. Chem. 2011, 123, 7450–7452; b) C. Xu, Q. Shen,
Org. Lett. 2014, 16, 2046–2049; c) G. Yin, I. Kalvet, F. Schoenebeck,
Angew. Chem. Int. Ed. 2015, 54, 6809–6813; Angew. Chem. 2015, 127,
6913–6917.
Received: July 24, 2015
Published online on September 1, 2015
Chem. Eur. J. 2015, 21, 14324 – 14327
www.chemeurj.org
14327
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim