Electrophilic trifluoromethanesulfanylation of indole derivatives

Article abstract of DOI:10.1016/j.jfluchem.2011.02.005

Trifluoromethanesulfanylamides constitute a family of easily available reagents which could provide efficient ways to perform electrophilic trifluoromethanesulfanylation. In particular they are able to react with electron-rich aromatic compounds, more particularly with indoles, to yield expected CF₃S-subtituted molecules with good results.

Full text of DOI:10.1016/j.jfluchem.2011.02.005

Journal of Fluorine Chemistry 134 (2012) 160–163
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Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Electrophilic trifluoromethanesulfanylation of indole derivatives§
a
a,
b
a,
*
*
´
´
Aurelien Ferry , Thierry Billard , Eric Bacque , Bernard R. Langlois
a
´
´
Universite de Lyon, Universite Lyon 1, CNRS ICBMS (UMR CNRS 5246) – Laboratoire SURCOOF, 43 Bd du 11 novembre 1918, Bat Chevreul, F-69622 Villeurbanne, France
b Sanofi-Aventis S.A. 136, Quai Jules Guesde, BP 14, 94403 Vitry-Sur-Seine Cedex, France
A R T I C L E I N F O
A B S T R A C T
Article history:
Trifluoromethanesulfanylamides constitute a family of easily available reagents which could provide
efficient ways to perform electrophilic trifluoromethanesulfanylation. In particular they are able to react
with electron-rich aromatic compounds, more particularly with indoles, to yield expected CF3S-
subtituted molecules with good results.
Received 10 January 2011
Received in revised form 31 January 2011
Accepted 1 February 2011
Available online 26 February 2011
ß 2011 Elsevier B.V. All rights reserved.
Keywords:
Trifluoromethanesulfanylamide
Fluorine
Aromatic electrophilic substitution
Trifluoromethylthio group
Indoles
1. Introduction
strategies [7]. The first one is the building of the CF3S moiety by
halogen–fluorine exchange reactions. This strategy is used on the
Because of the specific physico-chemical properties of fluorine
[1,2], organofluorine chemistry has been steadily growing to
become, today, a field of great importance with a distinctive role in
highly diverse technological developments (fluoropolymers, phar-
maceutical and agrochemical products, materials science, medical
imaging, etc.) [3,4].
industrial scale, but is generally limited to aromatic compounds
[8]. The second method consists in grafting a CF3 group onto a
sulfur atom of the substrate. Such
a strategy requires the
preliminary synthesis of the sulfur-containing precursor. Trifluor-
omethylations of a sulfur atom have been essentially performed
via nucleophilic [9] or radical trifluoromethylation [10] of
disulfides, thiocyanates or thiols. A few electrophilic trifluoro-
methylations of thiols and thiolates have been also reported [11].
The most direct method remains the direct introduction of the CF3S
group onto molecules. Radical and electrophilic hydrogen sub-
stitutions have been essentially performed with CF3SCl [12],
which, however, is a very toxic reagent. Some nucleophilic
reactions have been also realized by using stabilized forms of
the unstable CF3S anion, but, apart CF3SCu whose reactivity is
relatively limited [13o], such reagents are, generally, not stable
enough to be stored for a long time [13].
These last years, the association of
fluorinated groups has attracted a special interest. In particular
the CF3S moiety exhibits high hydrophobicity parameter
R = 1.44) [5] and, thereby, compounds bearing this group are
a heteroatom with
a
(
p
potentially important targets in the pharmaceutical and agro-
chemical fields [2(b,c),6].
Numerous methods are now available to introduce this function
onto organic substrates, divided, essentially, into three distinct
§
Consequently, until recently, there was no efficient and easily
Description of the laboratory: Our laboratory is involved in fluorine chemistry
available reagent to introduce directly
molecules by an electrophilic way.
a CF3S moiety onto
following three principal themes. The first one is a methodological aspect where we
are interested in the development of new methods or reagents to introduce fluorine
or fluorinated groups onto molecules. In particular, we focus our interest on the CF3
moiety and on substituents associating CF3 with heteroatoms (CF3O, CF3S, etc.). The
second theme is devoted to the applications of our previous methodologies for the
development of new fluorinated building-blocks and their application for the
synthesis of potentially bioactive fluorinated compounds. Finally, we are also
implied in medical imaging (PET scan) by developing new ligands, radiolabelled
with 18F nucleide, in particular for brain studies. For this purpose we develop also
new methods of radiolabelling to introduce this radioisotope.
2. Results and discussion
However, we have recently described an easy synthesis of
trifluoromethanesulfanylamides (1) [14] and demonstrated that
such compounds could react with alkenes and alkynes,
under acidic activation, as an equivalent of the CF3S+ cation
(Scheme 1) [15].
* Corresponding author. Fax: +33 04 72 43 13 23.
E-mail address: billard@univ-lyon1.fr (T. Billard).
0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.02.005

A. Ferry et al. / Journal of Fluorine Chemistry 134 (2012) 160–163
161
Table 1
Trifluoromethanesulfanylation of 1,3-dimethoxybenzene.
.
Entry
1
Acidic activation
T (8C)
t (h)
2 Crude yield (%)a
1
2
3
1a
1a
1b
p-TsOH (2.5 eq.)
BF3;Et2O (5 eq.)
BF3;Et2O (5 eq.)
50
RT
RT
18
24
24
94
61
69
aDetermined by 19F NMR titration with internal standard (PhOCF3).
Scheme 1. Trifluoromethanesulfanylation of alkenes with trifluoromethanesulfanylamides.
Scheme 2. Trifluoromethanesulfanylation of various aromatic compounds.
Since these reagents appear to be
electrophilic trifluoromethanesulfanylation, their use in electro-
philic aromatic substitutions has been envisaged.
First attempts have been realized with 1,3-dimethoxybenzene
as model substrate (Table 1).
All the conditions previously developed for the reaction of 1
with alkenes [15] have been tested. In contrast to alkenes, the best
results were obtained under activation with protic acids instead of
Lewis acids (Table 1, entry 1).
a
powerful tool for
attacked by the nucleophile which displaces the anilino moiety and
catches the CF3S moiety. The low d+ polarization of the sulfur atom
in such an intermediate could justify the need of very electron-rich
aromatic substrates to perform the reaction.
Since indole itself gave good yield, various substituted indoles
have been engaged in this reaction (Scheme 3).
In general, the expected products were obtained with good
yields. It can be noticed that no protections of functional group
are required (free NH indole, free NH2 (3g), free CO2H (3h)) to
achieve good yields. When the 3-position of indole is already
substituted, the 2-substitution is then observed (3f–3j). The low
isolated yield observed with 3g is essentially due to problems
during extraction of the product from the crude mixture since
the crude yield, observed by 19F NMR, is excellent. More
surprisingly, tryptophan did not give a good result (3i), whereas
tryptamine (3g) and indole propionic acid (3h) led to good
Under these selected conditions, other aromatic compounds
have been engaged (Scheme 2).
The results were disappointing since, in general, no reaction
have been observed, except with very electron-rich compounds,
such as indole, which underwent trifluoromethanesulfanylation
and led to the expected products. In the case of pyrrole, the acidic
conditions have triggered off polymerization before the expected
reaction took place.
yields. The protection of the amino group of 3i by
a
Such results suggest that the reacting intermediate is not a real
CF3S+ cation but a protonated form of 1a which could be directly
benzyloxycarbamate (3j) did not modify this disappointing
result.

162
A. Ferry et al. / Journal of Fluorine Chemistry 134 (2012) 160–163
Scheme 3. Trifluoromethanesulfanylation of various indoles (in parentheses, crude yield determined by 19F NMR titration with internal standard (PhOCF3)).
3
3. Conclusion
1JC–F = 310 Hz), 131.6, 126.9, 122.3, 115.6, 113.7, 95.6 (q, JC–
F = 2.6 Hz). 19F NMR (282 MHz, CDCl3):
d
= À44.87 (s). Anal. Calcd for
Trifluoromethanesulfinamides (1) have confirmed their ability
to realize electrophilic trifluoromethanesulfanylation and appear
to be a good alternative to toxic CF3SCl. Concerning electrophilic
aromatic substitutions, the operating conditions have to be
ameliorated to extend the panel of aromatic compounds to less
electron-rich substrates. However, some CF3S-substituted indoles
have been already obtained with good yields and such products
could already constitute interesting heterocyclic building-blocks
for further syntheses of bioactive molecules.
C9H5BrF3NS: C, 36.51; H, 1.70. Found: C, 36.68; H, 1.72.
4.5. 5-Methoxy-3-[(trifluoromethyl)thio]-indole (3c)
Yellow oil. 1H NMR (300 MHz, CDCl3):
d = 8.55 (s, 1H), 7.49 (d,
3J = 2.8 Hz, 1H), 7.30–7.26 (massif, 2H), 6.96 (m, 1H), 3.96 (s, 3H).
13C NMR (75 MHz, CDCl3):
d
= 156.0, 133.7 (q, 4JC–F = 1.1 Hz), 131.3,
1
3
130.7, 129.9 (q, JC–F = 310 Hz), 114.4, 113.0, 100.9, 95.4 (q, JC–
F = 2.6 Hz), 56.2. 19F NMR (282 MHz, CDCl3):
d
= À43.50 (s). Anal.
Calcd for C10H8F3NOS: C, 48.58; H, 3.26. Found: C, 48.51; H, 3.17.
4. Experimental
4.6. 5-Nitro-3-[(trifluoromethyl)thio]-indole (3d)
4.1. Typical procedure: synthesis of 2 or 3a–3f
Yellow solid. Mp = 151–152 8C. 1H NMR (300 MHz, acetone-d6):
To a solution of 1a (1 mmol) in dichloromethane (2 mL) were
added aromatic compounds (1 mmol) and then TsOH (2.5 mmol).
The reaction mixture was heated for 18 h at 50 8C. The organic phase
was washed with water and Et2O and dried over Na2SO4. After
removing solvent in vacuo, the crude was purified by flash
chromatography.
d
= 11.69 (bs, 1H), 8.63 (m, 1H), 8.20 (d, 3J = 2.3 Hz, 1H), 8.17 (m, 1H),
7.78 (m, 1H). 13C NMR (75 MHz, acetone-d6):
(q, 4JC–F = 1.2 Hz), 130.3 (q, 1JC–F = 309 Hz), 129.9, 119.0, 115.9, 114.0,
96.6(q, 3JC–F = 2.7 Hz). 19FNMR(282 MHz, acetone-d6):
d = 143.9, 140.7, 139.1
d
= À46.01(s).
Anal. Calcdfor C9H5F3N2O2S: C, 41.23; H, 1.92. Found: C, 41.36; H, 1.95.
4.7. Methyl-3-[(trifluoromethyl)thio]-1H-indole-5-carboxylate (3e)
White solid. Mp = 156–157 8C. 1H NMR (300 MHz, acetone-d6):
4.2. 2,4-Dimethoxy-1-[(trifluoromethyl)thio]benzene (2)
Yellow oil. 1H NMR (300 MHz, CDCl3):
d
= 7.53 (m, 1H), 6.54–
d
= 11.39 (bs, 1H), 8.46 (m, 1H), 8.00 (d, 3J = 2.8 Hz, 1H), 7.94 (dd,
3J = 8.6 Hz, 4J = 1.5 Hz, 1H), 7.65 (dd, 3J = 8.6 Hz, 5J = 0.7 Hz, 1H),
3.91 (s, 3H). 13C NMR (75 MHz, acetone-d6):
= 167.8, 140.2, 137.2
6.50 (massif, 2H), 3.88 (s, 3H), 3.83 (s, 3H). 13C NMR (75 MHz,
1
CDCl3):
d
= 164.3, 162.5, 140.6, 123.0 (q, JC–F = 309 Hz), 106.0,
d
3
4
1
103.6 (q, JC–F = 2.0 Hz), 99.6, 56.4, 55.9. 19F NMR (282 MHz,
CDCl3):
(q, JC–F = 1.1 Hz), 130.5 (q, JC–F = 309 Hz), 130.0, 124.8, 124.4,
121.8, 113.3, 95.4 (q, JC–F = 2.6 Hz), 52.2. 19F NMR (282 MHz,
3
d
= À44.12 (s). Anal. Calcd for C9H9F3O2S: C, 45.38; H, 3.81.
Found: C, 45.16; H, 3.67.
acetone-d6):
H, 2.93. Found: C, 48.07; H, 3.01.
d
= À46.13 (s). Anal. Calcd for C11H8F3NO2S: C, 48.00;
4.3. 3-[(Trifluoromethyl)thio]-indole (3a) [12k]
4.8. 3-Methyl-2-[(trifluoromethyl)thio]-indole (3f)
Yellow solid. Mp = 95–96 8C. 1H NMR (300 MHz, CDCl3):
d = 8.20
Yellow oil. 1H NMR (300 MHz, CDCl3):
d = 8.56 (bs, 1H), 7.80 (m,
1H), 7.53 (d, 3J = 2.6 Hz, 1H), 7.42 (m, 1H), 7.32–7.24 (massif, 2H).
13C NMR (75 MHz, CDCl3):
(q, JC–F = 310 Hz), 129.9, 123.8, 122.0, 119.7, 112.2, 95.7 (q, JC–
F = 2.4 Hz). 19F NMR (282 MHz, CDCl3):
d
= 136.5, 133.4 (q, 4JC–F = 1.1 Hz), 130.0
(bs, 1H), 7.70 (m, 1H), 7.44–7.37 (massif, 2H), 7.26 (m, 1H). 13C NMR
1
3
1
(75 MHz, CDCl3):
d
= 137.8, 129.2 (q, JC–F = 312 Hz), 128.4, 125.6,
4
3
d
= À45.04 (s).
124.1 (q, JC–F = 1.1 Hz), 120.49, 120.47, 113.5 (q, JC–F = 2.4 Hz),
111.6, 9.8. 19F NMR (282 MHz, CDCl3):
= À43.50 (s). Anal. Calcd for
C10H8F3NS: C, 51.94; H, 3.49. Found: C, 51.90; H, 3.41.
d
4.4. 5-Bromo-3-[(trifluoromethyl)thio]-indole (3b)
Brown solid. Mp = 48–49 8C. 1H NMR (300 MHz, CDCl3):
d
= 8.58
4.9. 2-{2-[(Trifluoromethyl)thio]-1H-indol-3-yl}ethanamine (3g)
(s large, 1H), 7.94 (m, 1H), 7.49 (d, 3J = 2.8 Hz, 1H), 7.36 (dd,
3J = 8.4 Hz, 4J = 1.7 Hz, 1H), 7.25 (dd, 3J = 8.4 Hz, 5J = 0.2 Hz, 1H). 13
NMR (75 MHz, CDCl3):
= 135.1, 134.2 (q, 4JC–F = 1.1 Hz), 129.7 (q,
C
To a solution of 1a (1 mmol) in dichloromethane (4 mL) was
added tryptamine (1 mmol) then TsOH (2.5 mmol). The reaction
d

A. Ferry et al. / Journal of Fluorine Chemistry 134 (2012) 160–163
163
(f) T. Umemoto, S. Ishihara, M. Harada, Daikin, JP 97207900, 1999 (Chem. Abstr.
130:209495).
mixture was heated for 18 h at 50 8C. The reacting mixture was
then filtered and the solid was washed with Et2O. After removing
solvent in vacuo, the filtrate was dissolved in CH2Cl2 and washed
with aqueous NaHCO3 (6%). The organic phase was dried over
Na2SO4 and after removing solvent in vacuo, the crude was purified
by flash chromatography (CH2Cl2/MeOH: 95/5 + 0.5% Et3N).
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2180–2182;
Brown solid. Mp = 50–51 8C. 1H NMR (300 MHz, CDCl3):
(bs, 1H), 7.65(m, 1H), 7.36–7.25(massif,2H), 7.14(m, 1H), 3.12–3.10
d = 9.69
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6677–6678;
(massif, 4H), 2.27(bs large, 2H). 13C NMR (75 MHz, CDCl3):
d = 138.2,
128.9 (q, 1JC–F = 312 Hz), 127.6, 125.0, 124.6 (q, 4JC–F = 1.1 Hz), 120.5,
120.3, 114.3 (q, 3JC–F = 2.4 Hz), 111.9, 42.7, 29.1. 19F NMR (282 MHz,
CDCl3):
d
= À43.39 (s). Anal. Calcd forC11H11F3N2S: C, 50.76; H, 4.26;
N, 10.76. Found: C, 51.11; H, 4.49; N, 11.04.
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4.10. 3-{2-[(Trifluoromethyl)thio]-indol-3-yl}propanoic acid (3h)
To a solution of 1a (1 mmol) in dichloromethane (2 mL) was
added (3-propio)indolic acid (1 mmol) then TsOH (2.5 mmol). The
reaction mixture was heated for 18 h at 50 8C. The reacting mixture
was washed with H2O. The organic phase was dried over Na2SO4 and
after removing solvent in vacuo, the product 3h is directly obtained.
Beige solid. Mp = 103–104 8C. 1H NMR (300 MHz, CDCl3):
`
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(b) J.F. Harris, J. Am. Chem. Soc. 84 (1962) 3148–3153;
(c) J.F. Harris, J. Org. Chem. 31 (1966) 931–935;
d
= 8.34 (bs, 2H,), 7.66 (m, 1H), 7.40–7.29 (massif, 2H), 7.18 (m,
1H), 3.28 (t, 3J = 8.0 Hz, 2H), 2.74 (t, 3J = 8.0 Hz, 2H). 13C NMR
1
(75 MHz, CDCl3):
125.7 (q, JC–F = 1.1 Hz), 125.3, 120.8, 120.2, 113.9 (q, JC–
F = 2.4 Hz), 111.9, 35.1, 20.5. 19F NMR (282 MHz, CDCl3):
d
= 179.6, 138.0, 128.9 (q, JC–F = 311 Hz), 127.2,
4
3
(d) W. Sheppard, S. Andreades, J.F. Harris, J. Org. Chem. 29 (1964) 898–900;
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= À43.22 (s). Anal. Calcd for C12H10F3NO2S: C, 49.82; H, 3.48.
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IN 178903, 1997 (Chem. Abstr. 140:375162).;
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