A new synthesis of trifluoromethyl sulfides utilizing thiocyanates and fluoroform

Article abstract of DOI:10.1016/j.jfluchem.2014.09.026

Fluoroform is a potent greenhouse gas which should not be released to the atmosphere. Large amounts of it are stored and wait for new and useful reactions to be based on it. One such general reaction that is described in this paper is its use in preparation of the important organic trifluoromethyl sulfides. Aliphatic, aromatic and heterocyclic thiocyanates are easy to prepare. They were reacted with fluoroform-based CuCF₃ to form the corresponding (trifluoromethyl)thio derivatives.

Full text of DOI:10.1016/j.jfluchem.2014.09.026

Accepted Manuscript
Title: A New Synthesis of Trifluoromethyl Sulfides Utilizing
Thiocyanates and Fluoroform
Author: Shay Potash Shlomo Rozen
PII:
S0022-1139(14)00290-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2014.09.026
FLUOR 8443
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
13-8-2014
20-9-2014
23-9-2014
Please cite this article as: S. Potash, S. Rozen, A New Synthesis of Trifluoromethyl
Sulfides Utilizing Thiocyanates and Fluoroform, Journal of Fluorine Chemistry (2014),
http://dx.doi.org/10.1016/j.jfluchem.2014.09.026
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

A New Synthesis of Trifluoromethyl Sulfides Utilizing Thiocyanates and
Fluoroform
Shay Potash and Shlomo Rozen*
School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel 69978. Fax: +972 3 640
9293; Tel: +972 3 640 8378; E-mail: rozens@post.tau.ac.il
Graphical Abstract
RSCN
HCF3
CuCF3
RSCF3
KSCN,
BrSCN
RX, ArH, HetH
Highlights
•
An efficient and general way developed for preparing the most lipophilic SCF3
group.
•
•
The cheap fluoroform has been used as a source for the CF3 group.
CuCF3 was prepared with no stabilizers (e.g. Et3N/xHF) under atmospheric
pressure.
•
•
Aliphatic, aromatic and heterocyclic (trifluoromethyl)thio derivatives were
made.
RSCF3 are made by reacting thiocyanates, readily made from halides, with
CuCF3.
Abstract
Page 1 of 15

-2-
Fluoroform is a potent greenhouse gas which should not be released to the
atmosphere. Large amounts of it are stored and wait for new and useful reactions to
be based on it. One such general reaction that is described in this paper, is its use in
preparation of the important organic trifluoromethyl sulfides. Aliphatic, aromatic and
heterocyclic thiocyanates are easy to prepare. They were reacted with fluoroform
based CuCF3 to form the corresponding (trifluoromethyl)thio derivatives.
Introduction
Fluorinated compounds are continuously taking more prominent place in
various fields since they usually considerably modify molecules’ physical, chemical
and biological properties. These modifications result in materials, which are suitable
for diverse applications in the areas of medicinal chemistry materials science,
agrochemistry, and much more [1–3]. It is not surprising, thus, that a large number of
existing pharmaceuticals and agrochemicals and up to 50% of those under
development contain at least one fluorine atom [4].
The trifluoromethyl group is very much associated with remarkable biological
properties, mainly due to the increased lipophilicity it offers [5,6]. Two main methods
are used for constructing such trifluoromethylated compounds. One consists of
transferring the whole CF3 group from an appropriate reagent such as Ruppert-
Prakash Me3SiCF3 [7], CF3I [8], (trifluoromethyl)dibenzothio or seleno salt systems
[9], CF3COOK [10], Togni reagent [11] and alike. The other main route focuses on
constructing the CF3 group at desired sites [12].
Among the various trifluoromethyl moieties the trifluoromethylthio one,
SCF3, is of special interest since it has one of the highest lipophilicity’s parameter
values [13]. Due to the importance of these trifluoromethylated sulfides, several
Page 2 of 15

-3-
synthetic methods have been developed for their preparation. Billard compiled an
impressive review describing the formation of the C-SCF3 bond by either electrophilic
or nucleophilic trifluorothiomethylating agents based on the toxic CF3SCl and some
of its metal derivatives CF3SM (M = Ag, Cu or NR2) [14]. Another approach, mostly
confined to aromatics, use CF3SiMe3/S8 mixture which was reacted either with aryl
boronic acid derivatives or aryl iodides [15]. Trifluorothiomethyl-iodonium reagents
have also been successfully employed [16]. It should be pointed out that most of these
reactions proceed with racemization of asymmetric carbon centers when relevant.
Other synthetic methods for the preparation of trifluoromethyl sulfides used CF3I or
the now banned CF3Br [17]. One of the current industrial method for the preparation
of trifluoromethyl sulfides is by chlorination followed by chlorine–fluorine exchange
reactions of the trichloromethyl sulfides with HF/SbF3/SbF5 a method requiring harsh
conditions frequently responsible to undesired side reactions [Error! Bookmark not
defined.,18].
The use of fluoroform, CHF3, has long been recognized as an attractive
trifluoromethylation method. Fluoroform is a side product of manufacturing Teflon®,
PVDF, refrigerants and fire extinguishing agents. It is generated in large volumes of
over 20000 tons yearly [19,20]. However, although nontoxic and with zero ozone
depleting potential, it is a very potent greenhouse compound. As a result, the 1997
Kyoto protocol obligated industrialized countries to reduce its emissions.
Consequently, as the disposal of this stable compound by destruction is rather
expensive [Error! Bookmark not defined.], large quantities of fluoroform are
currently in storage waiting for new reactions to utilize it [Error! Bookmark not
defined.].
In an effort to put fluoroform to good use, research efforts have been invested
Page 3 of 15

-4-
to take advantage of it as a synthetic reagent. Indeed CHF3, along with strong bases,
was reacted with carbonyls to form new C-CF3 bonds [21]. Prakash and Olah reported
the fluoroform-derived trifluoromethylation of C, Si and B centers using suitable
electrophiles and amide bases at very low temperatures and mild reaction conditions
[Error! Bookmark not defined.]. Other contributions have recently been published
by Grushin, who prepared the relatively stable CuCF3 reagent using fluoroform and t-
BuOK/CuCl system for trifluoromethylation of aromatic halides, aryl boronic acid
and formation of α-trifluoromethyl ketones [Error! Bookmark not defined.,22]. The
use of this fluoroform based nucleophilic trifluoromethylating agent, has attracted our
attention, while considering construction RS-CF3 derivatives. This task requires
besides the trifluoromethyl nucleophile, an appropriate sulfur electrophile. Disulfides
have been used as such electrophiles and indeed formed trifluoromethyl sulfides, but
the fact is that half of the organic disulfide is lost as a leaving group while the
trifluoromethylating nucleophile was Me3SiCF3 [23] and the base phosphazene [24]
both quite expensive agents. Organic thiocyanates seemed a natural contender for this
function, as they possess electrophilic sulfur. Such thiocyanates are easy to prepare
from inexpensive thiocyanate salts such as KSCN, from electrophilic XSCN reagents
(X = Cl, Br, SCN) or from the corresponding thiols and BrCN [25].
Results and Discussion
Our initial substrate was the commercial n-dodecyl thiocyanate, 1a which was
reacted with 1.5 molar equivalents of the fluoroform derived CuCF3. After a few
experiments it was found that the best conditions for the reaction were using non-
stabilized CuCF3, rather than the CuCF3/Et3N·3HF combination that was previously
employed mainly to suppress side products containing the O-t-Bu moiety [Error!
Bookmark not defined.b]. It was also found that unlike several previous works, there
Page 4 of 15

-5-
was no need for reaction vessels suitable for high-pressure procedures using CHF3
and t-BuOK/CuCl system for the preparation the active CuCF3 species. This
simplified procedure produced the desired trifluoromethyldodecyl sulfide (2a) in
quantitative yield within 5h at room temperature. 3-Phenylpropyl thiocyanate (1b)
[26] was similarly reacted with the CuCF3 suspension to form 3-
phenylpropyltrifluoromethyl sulfide (2b) also in quantitative yield. This compound
was previously prepared by the reaction of the corresponding disulfide with Me3SiCF3
but no yield was reported [27]. In order to demonstrate the efficiency of this reaction,
the doubly thiocyanate, 1,10-dithiocyanatodecane (1c) [28], was reacted with 3 mole-
equivalents of the fluoroform derived CuCF3 (50% excess) for 6h at room temperature
yielding the previously unknown 1,10-bis(trifluoromethylthio)decane (2c) in 90%
yield.
Secondary thiocyanates are also reactive towards the nucleophilic
trifluoromethylating reagent CuCF3. The reaction rate, however, seem to be affected
from steric factors as the reactions are slower and require moderate heating to reach
full conversion. Nonetheless, (3-thiocyanatobutyl)benzene (1d) [29] yielded the
previously unknown secondary 3-[(trifluoromethyl)thio]-1-phenylbutane (2d) in 6h at
o
45 C and in 75% yield. Similarly, the reaction of the trifluoromethylating agent
CuCF3 with the cyclic thiocyanatocyclohexane (1e) [30] yielded under similar
conditions the 1-[(trifluoromethyl)thio]cyclohexane (2e) (Scheme 1).
Aromatic thiocyanates could also be readily prepared and then successfully
employed in this reaction. 4-Tert-butylphenyl thiocyanate (1f) was formed by
electrophilic aromatic substitution of tert-butylbenzene using lead (II) thiocyanate
[31]. Its reaction with 1.5 molar equivalents of CuCF3 provided 1-
o
[(trifluoromethyl)thio]-4-tert-butylbenzene (2f) in 90% yield after 14h at 45 C. The
Page 5 of 15

-6-
2-thiocyanatonaphthalene (2g) was recently reported to be formed in 47% yield by the
reaction of the in-situ prepared sodium naphthalene-2-thiolate with CF3I [32]. As with
1f, we have used CHF3 based CuCF3 on 2-naphthyl thiocyanate (1g) and obtained the
desired 2g in 80% yield.
In one of his pioneering works, Grushin reported trifluoromethylation of some
o
chloro-aryl derivatives by CuCF3, reactions which required heating of up to 80 C
[Error! Bookmark not defined.]. Since the substitution of aromatic thiocyanate is
much faster, it is possible to get a clean reaction of 1,2-dichloro-4-thiocyanatobenzene
(1h) with 1.5 equivalent of the fluoroform based copper reagent, yielding 1-
[(trifluoromethyl)thio]-3,4-dichlorobenzene (2h) in 85% yield without affecting the
aromatic halogens. Heterocyclic trifluoromethyl sulfides such as 3-
[(trifluoromethyl)thio]-indole (2i) could also be obtained by starting with the
unprotected 3-indole thiocyanate, (1i), which in its turn, was prepared by electrophilic
aromatic substitution of indole with KSCN and Br2 (BrSCN) [33] (Scheme 1).
Scheme 1: From thiocyanates to trifluoromethyl sulfides
Page 6 of 15

-7-
CuCF3 (1.5 eq.)/ DMF
R SCF3
2
R SCN
CHF3/ t-BuOK/ CuCl
1
a
R = n-C12H25
> 95%
5h, R.T
b
R = Ph(CH2)3
5h, R.T
> 95%
90%a
(CH2)10
c R =
6h, R.T
6h, 45 oC
R = Ph(CH2)2CHMe
d
75%
60%
6h, 45 oC
e R = cyclo-C6H11
14h, 45 oC
90%
4-t-BuC6H4
R =
R =
f
14h, 45 oC
14h, 45 oC
g
2-naphtyl
80%
85%
h
i
R = 3,4-di-Cl-C6H3
14h, 45 oC
R =
N
50%
H
(a) using 3 mol/eq of CuCF3
Conclusion
In conclusion, a diverse series of trifluoromethyl sulfides was prepared from
the corresponding alkyl, aryl and heterocyclic thiocyanates. As these
trifluoromethylthio compounds gain popularity, it is important to find sustainable and
relatively easy procedure for their preparation. The use of fluoroform fulfills this
condition, as the disposal of this greenhouse gas has become a major issue in the last
decade.
Experimental
General Procedures:
Page 7 of 15

-8-
1H, 19F, and 13C NMR spectra were obtained with CDCl3 as solvent at 400,
376, and 100 MHz, respectively, with Me4Si as an internal standard for the 1H and 13C
NMR and CFCl3 for the 19F NMR spectra. HRMS sample of 2i was measured under
ESI conditions. In all other cases this method could not detect the molecular ion, so
we used successfully Amirav’s supersonic GC-MS technique. In these cases, the
isotope abundance analysis provided very satisfactory results, as shown for the
specific compounds. This type of analysis confirmed the proposed elemental formulas
as it ranked them in first place and hence as the best choice, with very good matching
factors of better than 940 (out of 999) [34].
General Trifluoromethylation Procedure:
To a two necked flask equipped with a glass pipette inlet for argon, 40 ml of
DMF were inserted and the solvent was degassed for 5 minutes. Then, 4.7 gr of finely
ground potassium tert-butoxide were added into the solution and stirred for about 5
minutes until most of the solid was dissolved. Two gr of copper (I) chloride were
added and the suspension turned black within a minute. This suspension was
vigorously stirred while argon was passed through for 1h at room temperature. The
argon inlet was replaced with a fluoroform inlet which was bubbled through the black
solution for 5 minutes at a rate of about 600 ml per minute (about 6 mole equivalents,
based of Cu). This procedure produced about 16mmol CuCF3 (calibrated using
19FNMR with PhCF3 as a standard). A measured volume was added to a DMF
solution of the thiocyanate ensuring about 50% excess of CuCF3 over the starting
thiocyanate and the suspension was stirred under argon atmosphere. The suspension
was added to cold water and extracted with ether. The ethereal solution was passed
through a short pad of celite to remove inorganic salts and evaporated. The product
was purified by flash column chromatography using Petrol Ether/EtOAc. Specific
Page 8 of 15

-9-
amounts of thiocyanates, CuCF3 suspension, reaction times and temperatures are
specified herein.
Thiocyanates formation:
Numerous thiocyanates have been prepared in the past. We have referenced the
known ones. In particular the primary thiocyanate 1b was prepared by us via the
substitution of (3-bromopropyl)benzene with 1.2 equiv. potassium thiocyanate in a
refluxing ethanolic solution for 2h. Bis–thiocyanate 1c was similarly prepared using 3
equivalent potassium thiocyanate and 1,10-dibromodecane. The secondary
thiocyanate 1d was made by the substitution of the corresponding tosylate with 1.5
equivalent potassium thiocyanate in a refluxing ethanol for 6h. Thiocyanates 1e,g,h
were prepared by drop-wise addition of an acetone solution of BrCN (1 equiv.) into a
solution of the corresponding thiol (1 equiv.) and triethylamine (1.5 equiv.) at 0oC.
The preparations of the electron-rich thiocyanates 1f and 1i were obtained by
electrophilic aromatic substitutions using in-situ prepared BrSCN as described in
reference Error! Bookmark not defined..
1-[(trifluoromethyl)thio]dodecane (2a) [35]. Prepared from commercial
thiocyanate 1a (1.00 g) and about 6.6 mmol CuCF3 as described in the general
1
procedure, in quantitative yield: 1.19 g, clear oil, H NMR 2.87 (2 H, t, J = 7.2 Hz),
1.68 (2 H, quin, J = 7.2 Hz), 1.39 (2 H, m), 1.26 (16 H, m), 0.88 (3 H, t, J = 6.8 Hz)
ppm. 13C NMR 131.3 (q, J = 304 Hz), 32.0, 29.9, 29.7, 29.6, 29.5, 29.4, 29.0, 28.6,
22.4, 14.1 ppm. 19F NMR -41.8 ppm (3 F, s). The common MS methods failed to
show any molecular peak. Amirav’s supersonic GC-MS revealed a strong molecular
ion peak of m/z 270.1 (M)+ with an isotope abundance analysis matching factor of
982 out of 999.
Page 9 of 15

-10-
1-[(trifluoromethyl)thio]-3-phenylpropane (2b) [Error! Bookmark not
defined.]. Prepared from thiocyanate 1b [Error! Bookmark not defined.] (1.24 g)
and fluoroform derived CuCF3 (about 10.5 mmol) as described in the general
1
procedure, in quantitative yield: 1.53 g, clear oil, H NMR 7.31 (2 H, m), 7.22 (1 H,
m), 7.19 (2 H, m), 2.89 (2 H, t, J = 7.2 Hz), 2.75 (2 H, t, J = 7.2 Hz), 2.04 (2 H, quin,
J = 7.2 Hz), ppm. 13C NMR 141.2, 131.9 (q, J = 311 Hz), 192.3, 129.2, 35.1, 31.7,
29.9 ppm. 19F NMR -41.6 ppm (3 F, s). The common MS methods failed to show any
molecular peak. Amirav’s supersonic GC-MS revealed a strong molecular ion peak of
m/z 220.0 (M)+ with an isotope abundance analysis matching factor of 996 out of 999.
1,10-bis[(trifluoromethyl)thio]decane (2c). Prepared from thiocyanate 1c
[Error! Bookmark not defined.] (0.80 g) and the fluoroform derived CuCF3 (about
1
9.4 mmol) as described in the general procedure, in 90% yield: 0.96 g, clear oil, H
NMR 2.87 (4 H, t, J = 7.2 Hz), 2.87 (2 H, t, J = 7.2 Hz), 1.69 (4 H, quin, J = 7.2 Hz),
13
1.3-1.4 (12 H, m) ppm. C NMR 131.3 (q, J = 304 Hz), 29.9, 29.4, 29.3, 28.9, 28.5
ppm. 19F NMR -40.0 ppm (3 F, s). The common MS methods failed to show any
molecular peak. Amirav’s supersonic GC-MS revealed a strong molecular ion peak of
m/z 342.1 (M)+ with an isotope abundance analysis matching factor of 989 out of 999.
Anal. calc. for C12H20F6S2: C, 42.09; H, 5.89; S, 18.73; F, 33.29. Found: C, 42.12; H,
5.88; S, 18.77; F, 33.64.
3-[(trifluoromethyl)thio]-1-phenylbutanane (2d). Prepared from thiocyanate
1d [Error! Bookmark not defined.] (0.62 g) and the fluoroform derived CuCF3
(about 4.9 mmol) as described in the general procedure, in 75% yield: 0.57 g, clear
1
oil, H NMR 7.29-7.32 (2 H, m), 7.19-7.23 (3 H, m), 3.31 (1 H, sextet, J = 6.8 Hz),
2.77 (2 H, t, J = 6.8 Hz), 1.88-2.00 (2 H, m), 1.47 (3 H, d, J = 6.8 Hz) ppm. 13C NMR
140.9, 131.2 (q, J = 304 Hz), 128.6, 128.4, 126.2, 40.7, 38.6, 32.9, 22.5 ppm. 19F
Page 10 of 15

-11-
NMR -39.4 ppm (3 F, s). The common MS methods failed to show any molecular
peak. Amirav’s supersonic GC-MS revealed a strong molecular ion peak of m/z 234.1
(M)+ with an isotope abundance analysis matching factor of 992 out of 999. Anal.
calc. for C11H13F3S: F, 24.33. Found: F, 23.83.
1-[(trifluoromethyl)thio]cyclohexane (2e) [Error! Bookmark not defined.].
Prepared from thiocyanate 1e [Error! Bookmark not defined.] (1.14 g) the
fluoroform derived CuCF3 (about 12.1 mmol) as described in the general procedure,
in 60% yield: 0.89 g, clear oil, 1H NMR 3.25 (1 H, m), 2.05 (2 H, m), 1.76 (2 H, m),
1.37-1.63 (5 H, m) ppm. 13C NMR 131.3 (q, J = 304 Hz), 44.0, 33.9, 25.7, 25.3 ppm.
19F NMR -39.7 ppm (3 F, s). The common MS methods failed to show any molecular
peak. Amirav’s supersonic GC-MS revealed a strong molecular ion peak of m/z 184.0
(M)+ with an isotope abundance analysis matching factor of 958 out of 999.
1-[(trifluoromethyl)thio]-4-tert-butylbenzene (2f) [Error! Bookmark not
defined.b]. Prepared from thiocyanate 1f [Error! Bookmark not defined.] (0.50 g)
and the fluoroform derived CuCF3 (about 3.9 mmol) as described in the general
procedure, in 90% yield: 0.55 g, clear oil, 1H NMR 7.58 (2 H, d, J = 8.4 Hz), 7.44 (2
H, d, J = 8.4 Hz), 1.34 (9 H, s) ppm. 13C NMR 154.4, 136.2, 129.8 (q, J = 306 Hz),
34.9, 31.2 ppm. 19F NMR -43.3 ppm (3 F, s). The common MS methods failed to
show any molecular peak. Amirav’s supersonic GC-MS revealed a strong molecular
ion peak of m/z 234.1 (M)+ with an isotope abundance analysis matching factor of
942 out of 999.
2-[(trifluoromethyl)thio]-naphthalene (2g) [Error! Bookmark not
defined.]. Prepared from thiocyanate 1g [Error! Bookmark not defined.] (0.70 g)
and the fluoroform derived CuCF3 (about 5.7 mmol) as described in the general
procedure, in 80% yield: 0.69 g, clear oil, 1H NMR 8.21 (1 H, s), 7.85-7.95 (3 H, m),
Page 11 of 15

-12-
7.47-69 (3 H, m) ppm. 13C NMR 137.1, 134.0, 133.4, 131.9, 129.8 (q, J = 310 Hz),
129.3, 128.3, 128.0, 127.9, 127.1, 1259, 121.6. 19F NMR -41.3 ppm (3 F, s). The
common MS methods failed to show any molecular peak. Amirav’s supersonic GC-
MS revealed a strong molecular ion peak of m/z 228.0 (M)+ with an isotope
abundance analysis matching factor of 991 out of 999.
1-[(trifluoromethyl)thio]-3,4-dichlorobenzene (2h) [Error! Bookmark not
defined.b]. Prepared from thiocyanate 1h [36] (0.80 g) and the fluoroform derived
CuCF3 (about 5.9 mmol) as described in the general procedure, in 85% yield: 0.82 g,
1
clear oil, H NMR 7.76 (1 H, m), 7.47-7.53 (2 H, m) ppm. 13C NMR 137.6, 136.1,
19
135.2, 133.6, 131.2, 129.1 (q, J = 310 Hz), 124.0 ppm. F NMR -42.7 ppm (3 F, s).
The common MS methods failed to show any molecular peak. Amirav’s supersonic
GC-MS revealed a strong molecular ion peak of m/z 245.9 (M)+ with an isotope
abundance analysis matching factor of 998 out of 999.
3-[(trifluoromethyl)thio]-indole (2i) [37]. Prepared from thiocyanate 1i
[Error! Bookmark not defined.] (1.25 g) and the fluoroform derived CuCF3 (about
10.8 mmol) as described in the general procedure, in 50% yield: 0.78 g, yellow oil, 1H
NMR 8.54 (1 H, brs), 7.82 (1 H, m), 7.54 (1 H, s), 7.43(1 H, m), 7.28-7.32(2 H, m)
ppm. 13C NMR 136.1, 134.2, 131.1, 132.1 (q, J = 330 Hz), 123.5, 121.7, 119.4, 111.7
ppm. 19F NMR -42.7 ppm (3 F, s). HRMS (ASAP): calcd. for C9H5F3NS (M–H)-
216.0095; found 216.0098.
Acknowledgement: This work was supported by the Israel Science Foundation.
References [1]
(a) Hiyama, T. Organofluorine Compounds: Chemistry and
Applications, Springer, Berlin (2000);
Page 12 of 15

-13-
[2]
[3]
[4]
(a) R. Berger, G. Resnati, P. Metrangolo, E. Weber, J. Hulliger, Chem. Soc.
Rev. 40 (2011) 3496;
(a) P. Kirsch, Modern Fluoroorganic Chemistry: Synthesis Reactivity,
Applications, Wiley, Weinheim, Germany (2013);
F. Giornal, S. Pazenok, L. Rodefeld, N. Lui, N, J. Vors, F. R. Leroux, J.
Fluorine Chem. 152 (2013) 2.
[5]
[6]
R. P. Singh, J. M. Shreeve, Tetrahedron, 56 (2000) 7613.
(a) C. A. Lipinski, F. Lombardo, B. W. Dominy, P. J. Feeney, Adv. Drug
Delivery Rev. 23 (1997) 3;
[7]
G. K. S. Prakash, C. Panja, H. Vaghoo, V. Surampudi, R. Kultyshev, M.
Mandal, G. Rasul, T. Mathew, G. A. Olah, J. Org. Chem. 71 (2006) 6806.
P. Chen, G. Liu, Synthesis (2013) 2919.
[8]
[9]
T. Umemoto, Chem. Rev. 96 (1996) 1757.
[10] M. Chen, S. L. Buchwald, Angew. Chem. Int. Ed. 52 (2013) 11628.
[11] T. Liu, Q. Shen, Org. Lett. 13, (2011) 2342.
[12] (a) R. Sasson, S. Rozen, Tetrahedron 61 (2005) 1083;
[13] C. Hansch, A. Leo, R. W. Taft, Chem. Rev. 91 (1991) 165.
[14] F. Toulgoat, S. Alazet, T. Billard, Eur. J. Org. Chem. (2014) 2415.
[15] (a) L. Zhai, Y. Li, J. Yin, K. Jin, R. Zhang, X. Fu, C. Duan, Tetrahedron 69
(2013) 10262;
[16] X. Wang, T. Yang, X. Cheng, Q. Shen, Angew. Chem. Int. Ed. 52 (2013)
12860.
[17] (a) C. Wakselman, M. Tordeux, J. Org Chem. 50 (1985) 4047;
[18] (a) T. Umemoto, S. Ishihara and M. Harada, JP11049742A, (1999) (Chem.
Abstr.130:209495);
Page 13 of 15

-14-
[19] A. Lishchynskyi, M. A. Novikov, E. Martin, E. C. Escudero-Adan, P. Novak,
V. V. Grushin, J. Org. Chem. 78 (2013) 11126.
[20] G. K. S. Prakash, P. V. Jog, P. T. D. Batamack, G. A. Olah, Science, 338
(2012) 1324.
[21] (a) S. Large-Radix, T. Billard, B. R. Langlois, J. Fluorine Chem. 124 (2003)
147;
[22] (a) A. I. Konovalov, J. Benet-Buchholz, E. Martin, V. V. Grushin, Angew.
Chem. Int. Ed. 52 (2013) 11637;
[23] (a) T. Billard, B. R. Langlois, Tetrahedron Lett. 37 (1996) 6865.
[24] H. Kawai, Z. Yuan, E. Tokunaga, N. Shibata, Org. Biomol. Chem. 11 (2013)
1446.
[25] (a) Y. Q. Wu, in Science of Synthesis 18 (2005) 17. Eds. J. G. Knight and R.
G. S. Berlinck;
[26] E. Bergman, J. Chem. Soc. (1935) 1361.
[27] J. W. Cubbage, Y. Gau, R. D. McCulla, W. S. Jenks, J. Org. Chem. 66 (2001)
8722.
[28] L. C. F. Blackman, M. J. S. Dewar, J. Chem. Soc. (1957) 162.
[29] Y. Liu, Y. Xu, S. H. Jung, J. Chae, Synlett. 23 (2012) 2692.
[30] P. Allen Jr., J. Am. Chem. Soc. 57 (1935) 198.
[31] S. Uemura, A. Onoe, H. Okazaki and M. Okano, Bull. Chem. Soc. Jpn. 48
(1975) 619.
[32] A. Harsanyi, E. Dorko, A. Csapo, T. Bako, C. Peltz, J. Rabai, J. Fluorine
Chem. 132 (2011) 1241.
[33] M. S. Grant, H. R. Snyder, J. Am. Chem. Soc. 82 (1960) 2742.
Page 14 of 15

-15-
[34] (a) A. Amirav, A. Gordin, M. Poliak, A. B. Fialkov, J. Mass Spectrom. 43
(2008) 141;
[35] F. Baert, J. Colomb, T. Billard, Angew. Chem. Int. Ed. 51 (2012) 10382.
[36] K. Pilgram, D. D. Phillips, J. Org. Chem. 30 (1965) 2388.
[37] A. Haas, U. Niemann, Chem. Ber. 110 (1977) 67.
Page 15 of 15