I. Gallardo, G. Guirado, J. Marquet
FULL PAPER
was then kept under nitrogen, and an electrolyte solution of
NEt4BF4 (0.2171 g) in DMF (5 mL) was added carefully. The crude
product [or mixture of product(s) and reactants] was purified or
separated by chromatography on silica gel eluting with chloroform.
3-(2-Chloro-3-nitro-4-pyridyl)-2-butanone (11)was obtained as the
sole product (40 mg, 57%), besides 40% (20 mg) of recovered unre-
acted starting material, 2-chloro-3-nitropyridine.
a variety of functionalized carbon substituents and provides
access to many synthetically useful intermediates.
The use of electrochemical techniques to oxidize the σH
complexes allows the selection of the oxidation potential
that is required in each case. In this way, more selective
oxidations can be achieved and more positive potentials can
be applied than by using chemical oxidizing agents. More-
over, the use of a clean technology permits the recovery of
the unreacted starting material.
1-(4-Nitrophenyl)acetone (6):[9] Table 1, Entry 1. 1H NMR
(250 MHz, CD3CN): δ ϭ 7.89 (d, J ϭ 8.38 Hz, 2 H), 7.34 (d, J ϭ
8.38 Hz, 2 H), 3.59 (s, 2 H), 2.42 (s, 3 H). 13C NMR (60 MHz,
CD3CN): δ ϭ 25.56, 58.50, 128.02, 128.92, 148.05, 155.05, 198.05.
Experimental Section
3-(4-Nitrophenyl)-2-butanone (7a):[10] Table 1, Entry 2. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.33 (d, J ϭ 9.03 Hz, 2 H), 8.17 (d, J ϭ
9.03 Hz, 2 H), 3.82 (q, J ϭ 7.17 Hz, 1 H), 2.42 (s, 3 H), 1.30 (dd,
J ϭ 7.17 Hz, 3 H).
General Remarks
Electrochemical Measurements: The electrochemical cell and meas-
urement procedures for cyclic voltammetry have been described
previously.[8] All the potentials are reported vs. an aqueous satur-
ated calomel electrode. A glassy carbon disc was used as the
working electrode (0.05 mm diameter). Electrolyses were carried
out using a PAR 273A potentiostat. A graphite rod was used as
the working electrode.
3-(2-Nitrophenyl)-2-butanone (7b):[11] Table 1, Entry 2. 1H NMR
(250 MHz, CD3CN): δ ϭ 7.57 (m, 1 H), 7.55 (m, 1 H), 7.51 (m, 1
H), 7.19 (dd, J ϭ 6.53, J ϭ 2.18 Hz, 1 H), 2.39 (s, 3 H), 1.55 (dd,
J ϭ 7.18 Hz, 3 H).
1-(4-Nitrophenyl)-2-butanone (7c):[12] Table 1, Entry 2. 1H NMR
(250 MHz, CD3CN): δ ϭ 7.89 (d, J ϭ 8.53 Hz, 2 H), 7.47 (d, J ϭ
8.53 Hz, 2 H), 3.60 (s, J ϭ 7.17 Hz, 2 H), 2.67 (q, J ϭ 7.2 Hz, 2
H), 1.12 (t, J ϭ 7.2 Hz, 3 H).
Materials: DMF (SDS, ‘‘pour syntheses peptidiques’’) and
nBu4NBF4 (Fluka, puriss.) were used without purification. Nitro-
benzene (1), 1,3-dinitrobenzene (2), and 1,3-dinitronaphthalene (4)
were purchased from Aldrich; 1,3,5-trinitrobenzene (3) was from
Supelco; 2-chloro-3-nitropyridine (5) was from Acros Organics;
potassium tert-butoxide was from Aldrich. All the commercially
available reactants were of high purity and were used without puri-
fication.
3,3-Bis(4-nitrophenyl)-2-butanone (8):[13] Table 1, Entry 2. 1H NMR
(250 MHz, CD3CN): δ ϭ 7.84 (d, J ϭ 8.20 Hz, 2 H), 7.28 (d, J ϭ
8.20 Hz, 2 H), 2.51 (s, 3 H), 2.38 (s, 3 H). 13C NMR (60 MHz,
CD3CN): δ ϭ 25.49, 38.28, 50.74, 119.92, 126.95, 130.65, 131.68,
137.49, 153.15, 200.95.
4-Nitrophenylacetophenone (9):[9] Table 1, Entry 3. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.33 (dt, J ϭ 9.10 Hz, J ϭ 1.95 Hz, 2 H),
8.22 (tt, J ϭ 4.25 Hz, J ϭ 1.30 Hz, 1 H), 8.16 (dt, J ϭ 9.10 Hz,
J ϭ 1.95 Hz, 2 H), 7.89 (dt, J ϭ 8.52 Hz, J ϭ 1.30 Hz, 2 H), 7.19
(dt, J ϭ 8.52 Hz, J ϭ 1.30 Hz, 2 H), 3.59 (s, 2 H). 13C NMR
(60 MHz, CD3CN): δ ϭ 42.30, 119.34, 127.18, 128.02, 128.91,
130.30, 133.58, 134.96, 137.55, 143.90, 144.20, 197.30.
General Procedure for NASH in Nitroarenes: A solution of the
nitroarene (20 m) in a DMF/ketone mixture (6 mL), which con-
tained 0.1 NBu4BF4 (0.1646 g) as a supporting electrolyte, was
prepared under nitrogen. The corresponding σH complex was pre-
pared by the slow and careful addition of tert-butoxide (nitroarene/
base ratio 1:1, 1:1ϩ0.5, 1:2, depending on the individual case; see
text) to the solution of the nitroarene under nitrogen. The oxidation
peaks of the σH complexes were measured by cyclic voltammetry.
Electrolyses were then carried out at potentials ca. 100 mV more
positive that the value measured for each σH complex, using a
graphite rod as the working electrode. After the passage of 2 F/
mol (calculated on the basis of the initial concentration of the σH
complexes), the electrolysis was stopped and the mixture was sub-
sequently partitioned between water and toluene. The organic layer
was dried with Na2SO4, the solvents were evaporated, and the res-
idue was analysed by gas chromatography and 1H NMR. The ana-
lysis showed the presence of nitro compounds. The final products
2,4-Dinitrophenylacetone (10):[5] Table 1, Entry 4. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.98 (d, J ϭ 2.50 Hz, 1 H), 8.45 (dd, J ϭ
8.45 Hz, J ϭ 2.50 Hz, 1 H), 7.65 (d, J ϭ 8.45 Hz, 1 H), 4.41 (s, 2
H), 2.29 (s, 3 H). 13C NMR (60 MHz, CD3CN): δ ϭ 29.88, 48.44,
120.81, 128.16, 136.05, 138.49, 148.10, 150.07, 202.86.
3-(2,4-Dinitrophenyl)-2-butanone (11):[7] Table 1, Entry 5. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.72 (d, J ϭ 2.50 Hz, 1 H), 8.48 (dd, J ϭ
8.67 Hz, J ϭ 2.50 Hz, 1 H), 7.75 (d, J ϭ 8.67 Hz, 1 H), 4.47 (q,
J ϭ 7.18 Hz, 1 H), 2.24 (s, 3 H), 1.55 (d, J ϭ 7.18 Hz, 3 H). 13C
NMR (60 MHz, CD3CN): δ ϭ 25.49, 34.28, 50.76, 119.92, 126.95,
130.65, 131.65, 137.49, 141.80, 205.45.
1
were analysed by gas chromatography, H NMR, 13C NMR, and
cyclic voltammetry and were identified by comparison of their
spectroscopic properties with those reported in the literature. The
yields were not optimized and were calculated by gas chromato-
2,4-Dinitrophenylacetophenone (12):[5] Table 1, Entry 6. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.85 (d, J ϭ 2.35 Hz, 1 H), 8.58 (dd, J ϭ
8.53 Hz, J ϭ 2.35 Hz, 1 H), 7.75 (d, J ϭ 8.53 Hz, 1 H), 7.38 (m, 5
H), 4.92 (s, 2 H). 13C NMR (60 MHz, CD3CN): δ ϭ 43.39, 119.34,
127.18, 128.02, 128.91, 130.30, 133.58, 134.96, 137.55, 140.20,
143.90, 197.3.
1
graphy and H NMR of the crude products. When acetophenone
was used as the ketone, the residue was distilled under reduced
pressure through a short fractionating column (b.p. 85 °C/8 Torr;
b.p. at atmospheric pressure 201 °C) in order to eliminate the excess
ketone present in the mixture.
2,4,6-Trinitrophenylacetone (13):[14] Table 1, Entry 7. 1H NMR
(250 MHz, CD3CN): δ ϭ 8.95 (s, 2 H), 4.49 (s, 2 H), 2.23 (s, 3 H).
Typical Procedure for Preparative Electrolysis. ؊ Generation of 3-
(2-Chloro-3-nitro-4-pyridyl)-2-butanone (11) by Preparative Electro-
lysis: A solution of the nitroarene (50 mg of 2-chloro-3-nitropyrid-
1-(2,4,6-Trinitrophenyl)-2-butanone (14):[15] Table 1, Entry 8. 1H
ine) in 2-butanone (5 mL) was prepared under nitrogen. Potassium NMR (250 MHz, CD3CN): δ ϭ 8.91 (s, 2 H), 3.60 (s, 2 H), 2.33
tert-butoxide (1.2 equiv.) was then carefully added. The mixture (q, J ϭ 7.20 Hz, 2 H), 1.00 (t, J ϭ 7.20 Hz, 3 H).
266
Eur. J. Org. Chem. 2002, 261Ϫ267