Chemistry of 2,4,6-trinitrobenzonitrile 1. Nitro group substitution in 2,4,6-trinitrobenzonitrile under the action of anionic nucleophiles. Factors favoring substitution of the ortho-nitro group

Article abstract of DOI:10.1023/A:1015043815242

The direction of the nitro group substitution (the ratio of the ortho/para substitution) in 2,4,6-trinitrobenzonitrile under the action of anionic nucleophiles (MeO^-, RS^-, and N₃^-) as well as of HCl was studied.

Full text of DOI:10.1023/A:1015043815242

Russian Chemical Bulletin, International Edition, Vol. 50, No. 12, pp. 2401—2405, December, 2001
2401
Chemistry of 2,4,6-trinitrobenzonitrile
1. Nitro group substitution in 2,4,6-trinitrobenzonitrile
under the action of anionic nucleophiles.
Factors favoring substitution of the ortho-nitro group
I. L. Dalinger, T. I. Cherkasova, S. S. Vorob´ev, A. V. Aleksandrov, G. P. Popova, and S. A. Shevelev«
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. E-mail: shevelev@cacr.ioc.ru
The direction of the nitro group substitution (the ratio of the ortho/para substitution) in
–
–
–
2,4,6-trinitrobenzonitrile under the action of anionic nucleophiles (MeO , RS , and N3 ) as
well as of HCl was studied. The factors favoring ortho substitution were revealed.
Key words: 2,4,6-trinitrobenzonitrile, nucleophilic substitution of nitro groups, anionic
nucleophiles, intramolecular cyclization, benzo[b]thiophenes.
The present work is a part of our systematic studies
aimed at the use of 2,4,6-trinitrotoluene (TNT) as a
readily accessible versatile starting material for the de-
sign of different types of valuable products.1
conditions (Schemes 1—4). The reaction conditions were
chosen (Table 1) so that they enabled the complete
conversion of TNB and its transformation into products
in preparative yields. The structures of the resulting
individual products or mixtures of isomers were estab-
lished by 1H NMR spectroscopy (in some cases, by 13C
NMR spectroscopy), mass spectrometry (EI), and IR
spectroscopy and confirmed by the satisfactory data
from elemental analysis.
In the reaction of TNB with MeONa in MeOH, one,
two, or even three nitro groups were replaced depending
on the reagent ratio and the reaction conditions (see
Scheme 1, Table 1), the first group being replaced even
at below-zero temperatures. This reaction afforded
methoxy derivatives 1—3 in high yields. It should be
noted that mono- or disubstitution gave rise to mixtures
of isomers (1 and 2), respectively. The effect of the
temperature on the course of the reaction was examined
using the monosubstitution reaction as an example. It
was found that the fraction of ortho-substitution prod-
ucts increased as the temperature was decreased (see
Table 1).
The effects of the nature of the solvent and the
structure of the nucleophile on the direction of the
replacement of the nitro groups in TNB were stud-
ied in reactions with thiols (PhCH2SH, PhSH, and
HSCH2CO2R, where R = Me or Et), which generated
the corresponding thiolate anions in situ under the ac-
tion of bases (see Schemes 2 and 3). It is known2,4 that
aromatic and aliphatic thiolate anions combine high
nucleophilicity in SNAr reactions and rather low basicity
(at least, their basicity is much lower than that of the
corresponding oxygen analogs).
From the practical standpoint, knowledge of the
characteristic features of the nitro group substitution
depending on the structure of the nitro compound and
reaction conditions is of fundamental importance in the
chemistry of TNT and products of transformations of its
methyl group (2,4,6-trinitro-substituted derivatives of
benzoic acid, benzaldehyde, their derivatives, 2,4,6-tri-
nitrostilbenes, etc.). These important characteristic fea-
tures are poorly studied not only for TNT and its
derivatives, but also for all aromatic meta-di- and
-polynitro compounds of various types.2
2,4,6-Trinitrobenzonitrile (TNB) is a readily acces-
sible TNT transformation product, which is potentially
valuable from the synthetic standpoint. This is prepared
from TNT under the action of NOCl in one technologi-
cal step.3 The replacement of the ortho-nitro group by
other functional groups which can undergo intramolecu-
lar cyclization involving the cyano group to form the
corresponding benzoannelated heterocycles is one of the
most attractive possibilities of the use of TNB in the
synthesis. However, it was necessary to ascertain before-
hand the regularities of the nucleophilic substitution of
the nitro groups in TNB, including the possibility of the
selective replacement of the ortho-nitro group.
Results and Discussion
We examined the reactions of some characteristic
representatives of anionic O-, S-, and N-nucleophiles,
–
–
viz., MeO , RS (R = PhCH2, Ph, or AlkOCOCH2),
We used solid K2CO3 (the molar ratio
TNB : thiol : K2CO3 = 1 : 1 : 1.8) as the deprotonating
–
and N3 , as well as of HCl with TNB under various
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2292—2296, December, 2001.
1066-5285/01/5012-2401 $25.00 © 2001 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001
Dalinger et al.
Table 1. Reactions of 2,4,6-trinitrobenzonitrile (TNB) with nucleophiles
Nucleophile (equivalents
with respect to TNB)
Solvent
T/°C
(t/h)
Product
Yielda
(%)
Ratio of the
ortho/para isomersb
MeONa (1)
MeONa (1)
MeONa (1)
MeONa (2)
MeONa (5)
PhCH2SH (1) + K2CO3 (1.8)
MeOH
MeOH
MeOH
MeOH
MeOH
–25 (7)
0 (7)
20 (4)
20 (7)
Refluxing (7)
0—2 (3)
1a + 1b
1a + 1b
1a + 1b
2a + 2b
3
93
∼90
93
85
88
2 : 1
3 : 2
1 : 1
2 : 1
—
DMF—H2O
(4 : 1)
4a + 4b
90
2 : 1
PhCH2SH (1) + K2CO3 (1.8)
PhCH2SH (1) + K2CO3 (1.8)
MeONa
MeCN
PhMe
MeOH
DMF—H2O
(4 : 1)
Refluxing (3)
Refluxing (8)
Refluxing (3)
0—2 (3)
4a + 4b
4a + 4b
6
90
40
68
76
3 : 1
5 : 1
—
c
PhSH (1) + K2CO3 (1.8)
7a + 7b
2 : 1
PhSH (1) + K2CO3 (1.8)
HSCH2CO2Me (1) + KOH (1.8)
PhMe
DMF—H2O
(4 : 1)
Refluxing (4)
20 (23)
7à
9
80
48
—
—
HSCH2CO2Et (1) + KOH (1.8)
DMF—H2O
(4 : 1)
20 (23)
10
54
—
NaN3 (1.2)
HCl
HCl
DMF
DMF
DMF
0—5 (3)
50—70 (1.5); 100 (1)
50—70 (2); refluxing (0.5)
11a + 11b
51
84
93
3 : 1
—
—
12
13
a With respect to the individual product or the purified mixture of isomers.
b The ratio of the isomers for the crude reaction products isolated.
c A mixture of 2-benzylsulfonyl-4,6-dinitrobenzonitrile (5a) and 4-benzylsulfonyl-2,6-dinitrobenzonitrile (5b) was used as the
starting substrate; the yield is given with respect to 5b.
agent except for the reactions with HSCH2CO2Alk,
where KOH was used. Under these conditions, only one
nitro group was replaced by the RS fragment.5
The effect of the polarity of the solvent on the
direction of the reaction was followed in the reaction
with PhCH2SH giving rise to a mixture of ortho/para
isomers 4a and 4b (see Table 1). The results obtained
demonstrate that the fraction of the ortho-substitution
product increases substantially as the polarity of the
solvent decreases in the series DMF—H2O, MeCN,
and PhMe.
Oxidation of a mixture of 4a and 4b (2 : 1) with
37% H2O2 in AcOH afforded a mixture of isomeric
sulfones 5a and 5b (1 : 1). Under the action of MeONa
Scheme 1
CN
CN
O2N
OMe
O2N
NO2
1 equiv. MeONa
+
NO2
1a
OMe
1b
CN
CN
CN
O2N
NO2
MeO
OMe
O2N
OMe
2 equiv. MeONa
+
NO2
TNB
NO2
OMe
2a
2b
CN
MeO
OMe
5 equiv. MeONa
OMe
3

Chemistry of 2,4,6-trinitrobenzonitrile
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001 2403
Scheme 2
CN
CN
CN
O2N
NO2
O2N
SCH2Ph
O2N
NO2
PhCH2SH/K2CO3
+
NO2
TNB
NO2
SCH2Ph
4b
4a
CN
CN
O2N
SO2CH2Ph
O2N
NO2
H2O2/AcOH
4a
+
4b
+
NO2
5a
SO2CH2Ph
5b
CN
MeO
OMe
MeONa
5b ( + 5a )
SO2CH2Ph
6
in boiling MeOH, these products were transformed into
a mixture of compounds from which the major product,
viz., sulfone 6, was isolated (see Scheme 2, Table 1).
The possible intramolecular cyclization of 5a was not
observed.
ortho/para isomers 7a and 7b. However, the reaction in
toluene proceeded regiospecifically. Thus exclusively the
ortho-nitro group was replaced to give the only product,
viz., sulfide 7a, in high yield (see Scheme 3, Table 1).
The reactions of HSCH2CO2R (R = Me or Et) with
TNB in the presence of KOH yielded the corresponding
alkyl 3-amino-4,6-dinitrobenzo[b]thiophene-2-carboxy-
The reaction of PhSH with TNB in aqueous DMF,
like the reaction of PhCH2SH, produced a mixture of
Scheme 3
CN
CN
O2N
SPh
O2N
NO2
PhSH/K2CO3
+
NO2
7a
SPh
7b
CN
CN
NO2
NH2
O2N
NO2
O2N
SCH2CO2R
HSCH2CO2R/KOH
CO2R
S
O2N
NO2
NO2
9: R = Me
10: R = Et
8
TNB
CN
CN
O2N
N3
O2N
NO2
NaN3
+
NO2
11a
N3
11b

2404
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001
Dalinger et al.
Scheme 4
ence of the above-considered factors on the selectivity of
the reaction call for further investigation.
CN
O2N
Cl
Experimental
100 °Ñ
The melting points were determined on a Boetius stage
(the heating rate was 4 deg min–1). The IR spectra were
recorded on a Specord M-80 spectrometer in KBr pellets. The
course of the reactions was monitored by TLC on Silufol
CN
NO2
12
O2N
NO2
HCl
DMF
1
UV-254 plates. The H and 13C NMR spectra were measured
CN
on a Bruker AC-200 spectrometer in DMSO-d6 (200.13 MHz
1
NO2
for H; 50.32 MHz for 13C; Me4Si as the internal standard).
Cl
Cl
153 °Ñ
2,4,6-Trinitrobenzonitrile was prepared by the reaction of
nitrosyl chloride with TNT in anhydrous pyridine.3
TNB
2-Methoxy-4,6-dinitrobenzonitrile (1a) and 4-methoxy-2,6-
dinitrobenzonitrile (1b). A solution of MeONa (13 mmol) in
MeOH (20 mL) was added to a solution of TNB (13 mmol) in
MeOH (80 mL). The reaction mixture was stirred under
conditions indicated in Table 1. Then the solvent was distilled
off. The solid residue was washed with water and dried to yield
a mixture of compounds 1a and 1b. 1H NMR, δ, 1a: 4.21
(s, OMe); 8.39 (s, H(3)); 8.51 (s, H(5)); 1b: 4.09 (s, OMe);
8.20 (s, H(3), H(5)).
NO2
13
lates 9 and 10, respectively, even in a polar medium
(MeCN—H2O) (see Scheme 3, Table 1). These com-
pounds are representatives of previously unknown
4,6-dinitrobenzo[b]thiophenes. According to the pub-
lished data,6 benzothiophenes 9 and 10 were generated
by base-catalyzed intramolecular cyclization of ortho-sub-
stitution product 8.
These results suggest that the lowering of the basicity
of the thiolate anion favors ortho-substitution in
TNB (in water, pKa values for PhCH2SH, PhSH, and
HSCH2CO2Et are 9.43,7 6.5,7 and 7.68,8 respectively;
in DMSO, pKa for PhCH2SH and PhSH are 15.4 9 and
10.3,9 respectively).
In the case of the azide ion, which combines low
basicity and high nucleophilicity, ortho-substitution pre-
vails even in a strongly polar solvent (DMF) (see
Scheme 3, Table 1). In this connection, recall that no
pronounced tendency for ortho-substitution was observed
in the case of the highly basic methoxide anion (see
Scheme 1).
Heating of TNB at 100 °C with DMF saturated with
gaseous HCl led to the replacement of only one of the
ortho-nitro groups to form 2-chloro-4,6-dinitrobenzo-
nitrile 12, whereas heating at 153 °C resulted in the
replacement of both ortho-nitro groups giving rise to
2,6-dichloro-4-nitrobenzonitrile 13 (see Scheme 4,
Table 1). It should be noted that the chloride ion,
which possesses very low basicity, acts as a moderate
nucleophile in SNAr reactions performed in aprotic
media.10
2,6-Dimethoxy-4-nitrobenzonitrile (2a) and 2,4-dimethoxy-
6-nitrobenzonitrile (2b). A solution of MeONa (36 mmol) in
MeOH (20 mL) was added to a solution of TNB (18 mmol) in
MeOH (100 mL). The reaction mixture was stirred at 20 °C for
7 h. The precipitate that formed was filtered off, washed with
water, and dried to yield a mixture of compounds 2a and 2b in
a ratio of 2 : 1. 1H NMR, δ, 2a: 4.05 (s, OMe); 7.42 (s, H(3),
H(5)); 2b: 4.05—4.00 (m, OMe); 7.15 (s, H(3)); 7.56 (s, H(5)).
2,4,6-Trimethoxybenzonitrile (3). A solution of MeONa
(23 mmol) in MeOH (10 mL) was added to a solution of TNB
(4.7 mmol) in MeOH (40 mL). The reaction mixture was
refluxed for 7 h and then cooled. The precipitate that formed
was filtered off, washed with water, dried, and recrystallized
from MeOH to yield compound 3, m.p. 142—144 °C.
Found (%): C, 61.87; H, 5.57; N, 7.30. C10H11NO3. Calcu-
1
lated (%): C, 62.17; H, 5.74; N, 7.25. H NMR, δ: 3.38 (s,
3 H, OMe); 3.39 (s, 6 H, OMe); 6.32 (s, 2 H, H(3), H(5)).
13C NMR, δ: 55.7; 56.1; 82.5; 90.9; 114.1; 163.1; 165.2.
2-Benzylthio-4,6-dinitrobenzonitrile (4a) and 4-benzylthio-
2,6-dinitrobenzonitrile (4b). A. A solution of K2CO3 (7.6 mmol)
in water (2 mL) was added to a solution of TNB (4.2 mmol)
and PhCH2SH (4.2 mmol) in DMF (8 mL) at 0—2 °C. The
reaction mixture was stirred at this temperature for 3 h and
then poured into water. The precipitate that formed was
filtered off, washed with water, and dried to yield a mixture of
sulfides 4a and 4b. Found (%): C, 53.14; H, 2.76; N, 13.34.
C14H9N3O4S. Calculated (%): C, 53.30; H, 2.86; N, 13.33.
1H NMR, δ, 4a: 4.70 (s, CH2); 7.30—7.50 (m, Ph); 8.67
(s, H(3)); 8.73 (s, H(5)); 4b: 4.65 (s, CH2); 7.30—7.50 (m, Ph);
8.50 (s, H(3), H(5)).
The results of the present study suggest that the
decrease in polarity of the solvent, reduction of the
reaction temperature, and the use of nucleophiles which
combine rather high nucleophilicity in SNAr reactions
and low basicity (i.e., soft Lewis bases), all other condi-
tions being the same, favor the selective nucleophilic
substitution of the ortho-nitro group in TNB. These
conclusions can serve as the basis for directed syntheses
starting from TNB. The synthesis of alkyl 3-amino-4,6-
dinitrobenzo[b]thiophene-2-carboxylates 9 and 10 pro-
vides an example. The reasons for the substantial influ-
B. A mixture of TNB (2.1 mmol), PhCH2SH (2.1 mmol),
and K2CO3 (3.8 mmol) in MeCN (5 mL) was refluxed for 3 h,
the solvent was distilled off, and the residue was dried to yield
a mixture of sulfides 4a and 4b.
C. A mixture of TNB (1.26 mmol), PhCH2SH (1.26 mmol),
and K2CO3 (2.3 mmol) in toluene (5 mL) was refluxed for 8 h,
the solvent was distilled off, and the solid residue was dried to
yield a mixture of sulfides 4a and 4b.
2-Benzylsulfonyl-4,6-dinitrobenzonitrile (5a) and 4-benzyl-
sulfonyl-2,6-benzonitrile (5b). A mixture of sulfides 4a and 4b
(2 : 1) (2.5 mmol), 37% H2O2 (18 mmol), and glacial AcOH
(5 mL) was refluxed for 3 h, cooled, poured into water, and

Chemistry of 2,4,6-trinitrobenzonitrile
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001 2405
extracted with ethyl acetate. The organic layer was washed
with water and dried with MgSO4, the solvent was distilled off,
and the solid residue was dried to yield a mixture of sulfones
5a and 5b in a ratio of 1 : 1 (74%). Found (%): C, 48.48;
H, 3.26; N, 12.01; S, 9.45. C14H9N3O6S. Calculated (%):
at 0—5 °C. The reaction mixture was stirred at this tempera-
ture for 3 h and then poured into water. The precipitate that
formed was filtered off, washed with water, and dried to yield
a mixture of azides 11a and 11b. 1H NMR, δ, 11a: 8.60
(s, H(3)); 8.65 (s, H(5)); 11b: 8.00 (s, H(3), H(5)). IR,
ν/cm–1: 1350 (NO2); 1540 (NO2); 2160 (N3); 2246 (CN).
2-Chloro-4,6-dinitrobenzonitrile (12). A solution of TNB
(4.2 mmol) in anhydrous DMF (6 mL) was saturated with
gaseous HCl at 50—60 °C with stirring for 1.5 h. The reaction
mixture was kept at 100—110 °C for 1 h, cooled, and poured
onto ice. The precipitate that formed was filtered off, washed
with water, and dried to yield chloride 12, m.p. 118—120 °C
(propan-2-ol). Found (%): C, 36.74; H, 0.94; N, 18.14;
Cl, 15.38. C7H2N3O4Cl. Calculated (%): C, 36.93; H, 0.88;
N, 18.46; Cl, 15.59. 1H NMR, δ: 8.89 (s, 1 H, H(3)); 9.04 (s,
1 H, H(5)). 13C NMR, δ: 119.2; 129.7; 139.9; 149.5; 150.5.
2,6-Dichloro-4-nitrobenzonitrile (13). A solution of TNB
(4.2 mmol) in anhydrous DMF (6 mL) was saturated with
gaseous HCl at 50—70 °C with stirring for 2 h. The reaction
mixture was refluxed for 30 min, cooled, and poured onto ice.
The precipitate that formed was filtered off, washed with water,
and dried to yield dichloride 13, m.p. 145—147 °C (EtOH).
Found (%): C, 38.58; H, 1.01; Cl, 32.70. C7H2N2O2Cl2.
Calculated (%): C, 38.71; H, 0.92; Cl, 32.72. 1H NMR, δ:
8.55 (s, 2 H, H(3), H(5)). 13C NMR, δ: 117.7; 123.8; 128.8;
143.7; 155.3.
1
C, 48.41; H, 2.59; N, 12.10; S, 9.22. H NMR, δ, 5a: 5.00
(s, CH2); 7.30—7.50 (m, Ph); 8.70 (s, H(3)); 9.20 (s, H(5));
5b: 5.00 (s, CH2); 7.30—7.50 (m, Ph); 8.80 (s, H(3), H(5)).
4-Benzylsulfonyl-2,6-dimethoxybenzonitrile (6). A mixture
of sulfones 5a and 5b (1 : 1) (2.4 mmol) and a 1.5% solution of
MeONa in MeOH (2 mL) was refluxed for 3 h, cooled, poured
into water, and extracted with ethyl acetate. The organic layer
was washed with water and dried with MgSO4. The solvent was
distilled off and an oil was obtained in a yield of 0.7 g. The oil
was passed through a column with silica gel (32—63 µm; a 5 : 2
CCl4—ethyl acetate mixture was used as the eluent) to yield
compound 6, m.p. 177—178 °C (EtOH). Found (%): C, 60.48;
H, 5.24; N, 4.39; S, 9.06. C16H15NO4S. Calculated (%):
C, 60.57; H, 4.73; N, 4.42; S, 10.09. 1H NMR, δ: 3.92 (s, 6 H,
OMe); 4.80 (s, 2 H, CH2); 7.08 (s, 2 H, H(3), H(5)); 7.21 (m,
2 H, Ph); 7.39 (m, 3 H, Ph).
4,6-Dinitro-2-phenylthiobenzonitrile (7a) and 2,6-dinitro-
4-phenylthiobenzonitrile (7b). A. A solution of K2CO3
(7.6 mmol) in water (2 mL) was added to a solution of TNB
(4.2 mmol) and PhSH (4.2 mmol) in DMF (8 mL) at 0—2 °C.
The reaction mixture was stirred at this temperature for 3 h
and then poured into water. The precipitate that formed was
filtered off, washed with water, and dried to yield a mixture of
sulfides 7a and 7b. 1H NMR, δ, 7a: 7.60 (m, Ph); 8.20
(s, H(3)); 8.70 (s, H(5)); 7b: 7.60 (m, Ph); 7.70 (s, H(3), H(5)).
B. A mixture of TNB (1.26 mmol), PhSH (1.26 mmol),
and K2CO3 (2.4 mmol) in toluene (5 mL) was refluxed for 4 h.
The solvent was distilled off and the solid residue was dried to
yield sulfide 7a, m.p. 152—154 °C (propan-2-ol). Found (%):
C, 51.62; H, 2.03; N, 13.85; S, 10.73; C13H7N3O4S. Calcu-
lated (%): C, 51.87; H, 2.32; N, 13.96; S, 10.65. 1H NMR, δ:
7.60 (m, 5 H, Ph); 8.20 (s, 1 H, H(3)); 8.70 (s, 1 H, H(5)).
Methyl 3-amino-4,6-dinitrobenzo[b]thiophene-2-carboxy-
late (9). A solution of KOH (7.5 mmol) in water (2 mL) was
carefully added dropwise with stirring to a solution of TNB
(4.2 mmol) and methyl thioglycolate (4.2 mmol) in MeCN
(10 mL) at 0—2 °C. The reaction mixture was stirred at 20 °C
for 3 h and then kept without stirring for 20 h. The precipitate
that formed was filtered off, washed several times with MeCN,
and dried to yield compound 9, m.p. 196—198 °C (propan-
2-ol). Found (%): C, 40.88; H, 2.62; N, 13.98; S, 11.01;
C10H7N3O6S. Calculated (%): C, 40.40; H, 2.35; N, 14.14;
S, 10.77. 1H NMR, δ: 3.85 (s, 3 H, Me); 6.60 (br.s, 2 H,
NH2); 8.70 (s, 1 H, H(7)); 9.40 (s, 1 H, H(5)).
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 01-03-
32261) and by the International Science and Technol-
ogy Center (ISTC, Grant 419).
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Ethyl 3-amino-4,6-dinitrobenzo[b]thiophene-2-carboxylate
(10) was prepared analogously, m.p. 200 °C (propan-2-ol).
Found (%): C, 42.87; H, 3.35; N, 13.23; S, 9.89. C11H9N3O6S.
Calculated (%): C, 42.44; H, 2.89; N, 13.50; S, 10.29.
1H NMR, δ: 1.36 (t, 3 H, Me, J = 4.4 Hz); 4.37 (q, 2 H, CH2,
J = 4.4 Hz); 6.56 (br.s, 2 H, NH2); 8.67 (s, 1 H, H(7)); 9.26
(s, 1 H, H(5)). 13C NMR, δ: 14.2; 61.3; 105.8; 116.9; 124.1;
–1
124.9; 125.5; 141.6; 144.9; 145.9; 163.7. IR (KBr), ν/cm
1350 (NO2); 1550 (NO2); 1730 (C=O).
:
2-Azido-4,6-dinitrobenzonitrile (11a) and 4-azido-2,6-
dinitrobenzonitrile (11b). Sodium azide (1.1 mmol) was added
to a solution of TNB (0.84 mmol) in anhydrous DMF (3 mL)
Received March 1, 2001;
in revised form June 14, 2001