V.M. Timoshenko, C. Portella / Journal of Fluorine Chemistry 130 (2009) 586–590
589
with CF3TMS under the conditions depicted in Entry 8 (Table 1).
Benzyltrifluoromethylsulfide (PhCH2SCF3) was indeed the main
product of the reaction. This sulfide has been characterized by
comparison of its NMR and GC–MS data with those reported in
literature [10]. Even this last step probably released a fluoride
anion from decomposition of the displaced unstable dithiocarbox-
ylate species, allowing the chain transfer, activation of CF3TMS, to
occur.
argon CF3TMS (0.11 ml, 0.75 mmol). After stirring at rt for 3 h
solvent and volatile products were removed under vacuum.
Residue was treated with light petroleum (10 ml), filtered through
Celite, concentrated and passed through a short column of silica gel
using light petroleum as eluent. The less polar fraction (Rf 0.65–
0.75) was collected to give after evaporation 107 mg (66%) of an
orange oil which contains, according to 19F NMR analysis (in
mol%): 3: 22%; 4: 6%; 5-(Z): 10%; 5-(E): 34%; 6: 8%; 7: 5%; 8: 7%;
recovered 1: 8%.
3. Conclusion
4.4. Reaction of dithioester 2 with CF3TMS
Thiophilic trifluoromethylation of perfluorodithioesters using
CF3TMS and nucleophilic initiators is the first step of a domino
transformation giving a perfluoroketene dithioacetal, then addi-
tion–elimination processes, and finally a nucleophilic substitution.
The salt derived from the initial thiophilic attack is stable enough to
be converted into the corresponding dithioacetal. These successive
chain reactions have close reaction rates so that we could not obtain
any ofthese new compounds withahighselectivity. Neverthelessall
products were well identified according to NMR and GC–MS
analysis, mainly because of well resolved 19F NMR spectra.
To a stirred mixture of dithioester 2 (150 mg, 0.5 mmol) and
anhydrous K2CO3 (7 mg, 0.05 mmol) in 4 ml of DME trimethyl(tri-
fluoromethyl)silane (0.11 ml, 0.75 mmol) was injected at argon
atmosphere. Reaction mixture was vigorously stirred at room
temperature for 4 h. The same work-up procedure as above gave
149 mg (80%) of an orange oil having, according to 19F NMR, the
composition: 5-(Z): 21%; 5-(E): 38%; 6: 15%; 7: 12%; 8: 7%;
recovered 2: 5%.
4.4.1. 1-Phenethylsulfanyl-1-trifluoromethylsulfanyl-2,2,2-
4. Experimental
trifluoroethane (3)
3
1H NMR (CDCl3):
d
7.30 m (5H, Ph), 4.46 q (1H, > CH, JHF
4.1. General remarks
7.5 Hz), 3.00 m (4H, 2CH2). GC–MS (m/e): 320 (M+, 10%), 219 (M+–
SCF3, 7%), 105 (PhCH2CH2+, 25%), 91 (PhCH2+, 100%). 19F NMR
19F NMR spectra were recorded on a Bruker AC-250 in CDCl3 as
the solvent and CFCl3 (
(CDCl3):
7.5 Hz, JFF 4.5 Hz).
d
À41.32 q (3F, SCF3, 5JFF 4.5 Hz), À69.64 dq (3F, CF3, 3JFH
5
d
= 0.00 ppm) as internal standard. MS data
were obtained on a Trace MS Thermoquest apparatus (GC–MS) at
70 eV in the electron impact mode. CsF was predried for 3 h at
300 8C before use. Anhydrous K2CO3 was used as received. Silica gel
Merck 9385 (40–63 mm) was used for chromatography. DME was
distilled over sodium benzophenone.
4.4.2. 2,2-Difluoro-1-phenethylsulfanyl-1-
trifluoromethylsulfanylethene (4)
19F NMR (CDCl3):
d
À42.41 dd (3F, SCF3, 5JFF 4.0 Hz, 5JFF 2.0 Hz),
À62.03 dq (1F, CF, 2JFF 16.0 Hz, 5JFF 2.0 Hz), À62.42 dq (1F, CF, 2JFF
16.0 Hz, 5JFF 4.0 Hz). GC–MS (m/e): 300 (M+, 4%), 280 (M+–HF, 6%),
105 (PhCH2CH2+, 100%), 91 (PhCH2+, 44%).
4.2. Dithioesters 1 and 2
Dithioesters 1 and 2 were prepared according to a reported
procedure [13] recently modified by us [3], by reaction of CF3TMS,
a fluoride salt and CS2, but using less expensive CsF instead of
TMAF, followed by alkylation of the resulting dithiocarboxylate
salt with (2-bromoethyl)benzene.
4.4.3. (Z)-1-Phenethylsulfanyl-1-trifluoromethylulfanyl-2,3,3,3-
tetrafluoropropene (5-Z)
19F NMR (CDCl3):
d
À39.77 d (3F, SCF3, 5JFF 7.5 Hz), À64.45 d (3F,
CF3, 3JFF 7.5 Hz), À90.28 septet (1F CF, 3,5JFF 7.5 Hz). GC–MS (m/e):
350 (M+, 1%), 281 (M+–CF3, 2%), 259 (M+–PhCH2, 2%), 144 (M+–
PhCH2CH2S–CF3, 4%), 125 (7%), 105 (PhCH2CH2+, 100%), 104
(PhCH2CHꢀ+, 78%), 91 (PhCH2+, 78%).
4.2.1. S-Phenethyl 2,2,2-trifluoroethanedithioate (1)
Yield 61%. Red oil, bp 85 8C (0.8 mbar). 1H NMR (CDCl3):
d
7.29 m (5H, Ph), 3.53 t (2H, CH2, 3JHH 7.6 Hz), 3.00 t (2H, CH2, 3JHH
7.6 Hz). 19F NMR (CDCl3): –65.6 s (CF3). 13C NMR (CDCl3):
4.4.4. (E)-1-Phenethylsulfanyl-1-trifluoromethylulfanyl-2,3,3,3-
d
d
tetrafluoropropene (5-E)
211.89 q (C S, 2JCF 35.5 Hz), 138.79 (Cipso), 128.93 (Cortho), 128.60
(Cmetha), 127.21 (Cpara), 118.29 q (CF3, JCF 279.1 Hz), 37.43 q (SCH2,
4JCF 1.1 Hz), 32.69 (CH2Ph). GC–MS (m/e): 250 (M+, 1%), 105
(PhCH2CH2+, 20%), 104 (PhCH2CHꢀ+, 100%), 91 (PhCH2+, 18%).
19F NMR (CDCl3):
d
À41.64 pentet (3F, SCF3,
J
2.5 Hz),
FF
5,6
À63.43 dq (3F, CF3, 3JFF 7.5 Hz, 6JFF 2.5 Hz), À90.77 dm (1F CF, 3JFF
7.5 Hz). GC–MS (m/e): 350 (M+, 3%), 281 (M+–CF3, 2%), 259 (M+–
PhCH2, 3%), 125 (5%), 144 (M+–PhCH2CH2S–CF3, 4%), 105
(PhCH2CH2+, 100%), 104 (PhCH2CHꢀ+, 75%), 91 (PhCH2+, 94%).
4.2.2. S-Phenethyl 2,2,3,3,3-pentafluoropropanedithioate (2)
Yield 65%. Red oil, bp 90 8C (0.5 mbar). 1H NMR (CDCl3):
d
4.4.5. 1-Phenethylsulfanyl-1-trifluoromethylulfanyl-2-
7.28 m (5H, Ph), 3.54 t (2H, CH2, 3JHH 7.7 Hz), 2.99 t (2H, CH2, 3JHH
trifluoromethyl-3,3,3-trifluoropropene (6)
7.7 Hz). 19F NMR (CDCl3):
d
À81.89 t (3F, CF3, 3JFF 2.0 Hz), À107.20 q
19F NMR (CDCl3):
d
À40.24 q (SCF3, 6JFF 3.5 Hz), À56.22 qq (CF3,
3
2
(2F, CF2, JFF 2.0 Hz). 13C NMR (CDCl3):
d
212.28 t (C S, JCF
4JFF 10.0 Hz, 6JFF 3.5 Hz), À58.11 q (CF3, 4JFF 10.0 Hz). GC–MS (m/e):
400 (M+, 1%), 331 (M+–CF3, 3%), 194 (M+–PhCH2CH2S–CF3, 7%), 105
(PhCH2CH2+, 93%), 104 (PhCH2CHꢀ+, 100%), 91 (PhCH2+, 65%).
24.5 Hz), 138.61 (Cipso), 128.94 (Cortho), 128.61 (Cmetha), 127.21
(Cpara), 117.78 qt (CF3, JCF 286.5 Hz, 2JCF 37.0 Hz), 110.92 td (CF2, JCF
4
261.5 Hz, 2JCF 36.8 Hz), 37.66 q (SCH2, JCF 2.2 Hz), 32.61 (CH2Ph).
GC–MS (m/e): 300 (M+, 1%), 162 (M+–PhCH2CH2S, 2%), 105
4.4.6. 1,1,1,4,4,4-Hexafluoro-2-phenethylsulfanyl-3-
(PhCH2CH2+, 22%), 104 (PhCH2CHꢀ+, 100%), 91 (PhCH2+, 16%).
trifluoromethylbut-2-ene (7)
5
4
19F NMR (CDCl3):
d
À58.39 qq (CF3, JFF 14.5 Hz, JFF 10.0 Hz),
4.3. Reaction of dithioester 1 with CF3TMS
À59.74 q (CF3, 4JFF 10.0 Hz), À60.03 q (CF3, 5JFF 14.5 Hz). GC–MS (m/
e): 368 (M+, 1%), 277 (M+–PhCH2, 3%), 194 (M+–PhCH2CH2–CF3, 4%),
To a stirred mixture of dithioester 1 (125 mg, 0.5 mmol) and
predried CsF (8 mg, 0.05 mmol) in 4 ml of DME, was added under
175 (PhCH2CH2+CF3, 6%), 105 (PhCH2CH2+, 100%), 104 (PhCH2CHꢀ+
98%), 91 (PhCH2+, 93%).
,