Direct Amination of Nitro(pentafluorosulfanyl)benzenes
1 F) ppm. MS (EI): m/z (%) = 264 (100) [M]+, 218 (25), 137 (15),
91 (13), 83 (26). HRMS (CI): calcd. for C6H6F5N2O2S [M + H]+
265.0070; found 265.0068.
perimental differences of chemical shifts was shown for 4g
than for 4gЈ or 4gЈЈ (Supporting Information, Table S1).
These findings are in accordance with the literature X-ray
crystal structure of unsubstituted 1,3-dihydrobenzoimid-
azole-2-thione, showing that the fused ring system is planar
and aromatic and that the thione is the predominant tauto-
mer in the solid state.[22] Condensation of 3 with an aque-
ous solution of glyoxal was used for the synthesis of quinox-
aline 5a.[23] Quinoxaline derivatives 5b and 5c were pre-
pared in excellent yield by using 1,2-diketones and catalytic
amounts of iodine in acetonitrile.[24] Finally, benzotriazole
6 was synthesized in high yield by the reaction of 3 with
nitrous acid (Scheme 3).
2-Nitro-4-(pentafluorosulfanyl)aniline (2b):[10] Pale brown solid
(1.316 g, 84%); m.p. 134–135 °C; Rf = 0.43 (PE/EtOAc, 70:30). IR
(film): ν = 3483, 3356, 1633, 1568, 1512, 1354, 1271, 1133, 1084,
˜
909, 847, 829 cm–1. 1H NMR (500 MHz, CDCl3): δ = 6.52 (br. s, 2
H), 6.89 (dquint., J = 9.3, 0.9 Hz, 1 H), 7.69 (dd, J = 9.3, 2.6 Hz,
1 H), 8.56 (d, J = 2.6 Hz, 1 H) ppm. 13C NMR (125.7 MHz,
CDCl3): δ = 118.5, 125.1 (quint., J = 5.0 Hz), 129.9, 132.3 (quint.,
J = 4.3 Hz), 142.1 (quint., J = 20.7 Hz), 146.0 ppm. 19F NMR
(376 MHz, CDCl3): δ = 63.6 (d, J = 151.1 Hz, 4 F), 83.9 (quint., J
= 151.1 Hz, 1 F) ppm. MS (EI): m/z (%) = 264 (100) [M]+, 245
(13), 234 (7), 218 (22), 110 (22), 91 (20), 83 (30). HRMS (CI): calcd.
for C6H6F5N2O2S [M + H]+ 265.0070; found 265.0066.
4-(Pentafluorosulfanyl)benzene-1,2-diamine (3):[10] A suspension of
Raney nickel (ca. 200 mg) in water was washed with ethanol
(2ϫ20 mL). Ethanol (25 mL) and 2 (1.00 g, 3.79 mmol) were
added, a balloon filled with hydrogen was attached, and the mix-
ture was stirred at room temperature for 2 h, followed by filtration,
washing with THF (3ϫ20 mL), and concentration of the filtrate
under reduced pressure. The resulting residue was purified by col-
umn chromatography (silica gel, PE/EtOAc) to give 3 as an orange
solid (719–764 mg, 81–86%); m.p. 72–74 °C; Rf = 0.26 (PE/EtOAc,
Figure 1. Possible tautomers of 4g and their ΔG298 values calcu-
lated at the B3LYP/6-31G* level of theory.
60:40). IR (film): ν = 3425, 3358, 3255, 3215, 1627, 1515, 1298,
˜
832, 804 cm–1. H NMR (500 MHz, CDCl3): δ = 3.53 (br. s, 4 H),
1
Conclusions
6.62 (dquint., J = 8.5, 1.0 Hz, 1 H), 7.08 (d, J = 2.5 Hz, 1 H), 7.11
(dd, J = 8.5, 2.5 Hz, 1 H) ppm. 13C NMR (125.7 MHz, CDCl3): δ
= 114.3, 114.4 (quint., J = 4.7 Hz), 118.5 (quint., J = 4.7 Hz),
133.1, 138.1, 145.6 (quint., J = 16.6 Hz) ppm. 19F NMR (376 MHz,
CDCl3): δ = 64.1 (d, J = 150.0 Hz, 4 F), 87.3 (quint., J = 150.0 Hz,
1 F) ppm. MS (EI): m/z (%) = 234 (100) [M]+, 126 (34), 107 (23),
98 (14), 80 (22). HRMS (CI): calcd. for C6H8F5N2S [M + H]+
235.0328; found 235.0321.
In conclusion, nitro(pentafluorosulfanyl)benzenes under-
went regioselective vicarious nucleophilic amination with
1,1,1-trimethylhydrazinium iodide in the presence of
tBuOK to give nitro(pentafluorosulfanyl)anilines in high
yields. Catalytic reduction with hydrogen in the presence of
Raney nickel provided 4-(pentafluorosulfanyl)benzene-1,2-
diamine in high yields, and simple condensation reactions
afforded new SF5-containing benzimidazoles, quinoxalines,
and benzotriazole.
Supporting Information (see footnote on the first page of this arti-
cle): General procedures, full characterization, and copies of the
1H NMR, 13C NMR, and 19F NMR spectra of compounds 2–6.
Experimental Section
Acknowledgments
General Procedure for the VNS Amination Reaction: A drying tube
with anhydrous CaCl2 was attached to a round-bottomed flask
(250 mL) with a stirring bar. The flask was charged with 1 (1.478 g,
5.93 mmol), TMHI (1.80 g, 8.90 mmol, 1.5 equiv.), and DMSO
(35 mL), and the flask was then immersed in a water bath (r.t.).
tBuOK (2.00 g, 17.8 mmol, 3.0 equiv.) was added, and the resulting
deep red mixture was stirred for 5 min, followed by the addition of
an aqueous saturated solution of NH4Cl (100 mL) and extraction
with EtOAc (3ϫ 80 mL). The combined organic phase was washed
with water (2ϫ 80 mL) and brine (80 mL), dried using anhydrous
MgSO4, and concentrated under reduced pressure. Purification by
column chromatography (silica gel, PE/EtOAc) gave desired prod-
uct 2.
This work was supported by the Academy of Sciences of the Czech
Republic (Research Plan AVZ40550506) and the Grant Agency of
the Czech Republic (P207/12/0072).
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2-Nitro-5-(pentafluorosulfanyl)aniline (2a): Pale orange solid
(1.285 g, 82%); m.p. 92–93 °C; Rf = 0.42 (PE/EtOAc, 80:20). IR
(film): ν = 3506, 3393, 1633, 1569, 1499, 1435, 1333, 1248, 846,
˜
1
839 cm–1. H NMR (500 MHz, CDCl3): δ = 6.30 (br. s, 2 H), 7.05
(dd, J = 9.4, 2.3 Hz, 1 H), 7.29 (d, J = 2.3 Hz, 1 H), 8.19 (dquint.,
J = 9.4, 1.0 Hz, 1 H) ppm. 13C NMR (125.7 MHz, CDCl3): δ =
113.8 (quint., J = 4.6 Hz), 117.1 (quint., J = 4.9 Hz), 127.0, 132.7,
144.2, 158.2 (quint., J = 18.7 Hz) ppm. 19F NMR (376 MHz,
CDCl3): δ = 61.2 (d, J = 150.5 Hz, 4 F), 81.3 (quint., J = 150.5 Hz,
Eur. J. Org. Chem. 2012, 2123–2126
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